Discrete Low-Drop Regulator

This circuit was designed to ensure that an amplifier circuit containing a TDA1516Q would not exceed its maximum supply voltage when the load is small. This amplifier is used in a PC to increase the audio power somewhat. The PC power supply, however, created so much interference that an additional power supply was required.

Discrete Low-Drop Regulator Circuit Diagram

The power supply has its own power trans-former with a secondary voltage of 12 V AC. After rectification and filtering this results in a DC voltage of about 16 V. The regulator consists of a P-channel MOSFET SJ117, the gate of which is driven via a voltage divider connected to T2. The base of T2 is held at a constant voltage by LED D2, so that the volt-age across emitter resistor R2 is also constant and therefore carries a constant cur-rent. When the output voltage is higher than about 13.5 V, zener diode D1 will start to con-duct and supply part of the current through R2 — as a result the MOSFET will be turned on a little less. In this way there is a balance point, where the output voltage will be a little over 13.5 V (1.5 V across R2 plus the 12 V zener voltage). The regulator is capable of deliver-ing up to about 2 A — in any case it is a good idea to fit the MOSFET with a heatsink.

It is possible to add an optional potentiometer in series with the 12-V zener diode, which will allow a small amount of adjustment of the output voltage.The relay at the AC powerline input ensures that the power supply is only turned on when the PC is turned on. This relay is driven from a 4-way power supply connector from the PC.

Author : Jac Hettema – Copyright: Elektor

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Power Controller for Electric Convector Heaters

In Autumn or Spring, the weather may be warm enough that we’d like to save money by shutting down the main heating system in our home and just use supplementary heating based on one or more electric convector heaters.

Even though these convectors are quite heavy consumers of electricity, this can be reduced by f it ting a power controller between the heaters and the AC power outlet, which will affect the effective power consumption of the convectors.

Power Controller for Electric Convector Heaters Schematic

The circuit diagram is based around the use of the emblematic NE555 IC, used here as an astable multivibrator with variable duty cycle (D= thigh/ T), but at a fixed operating frequency, given by: f= 1 / (0.693 × P1 × C6) = 0.0654 Hz

The duty cycle Dof the signal at the output (pin 3) of IC2 will change depending on the position of the wiper of potentiometer P1:

• If the wiper is at mid-travel, the duty cycle D will be 0.5;
• If the wiper is at the +12 V end, the IC2 output signal is zero and hence D = 0;
• If the wiper position takes it down to the voltage on C6, IC2’s output supplies a constant voltage of around 11 V and D = 1.

Byway of transistor T1, IC2 drives two MOC 3021 phototriacs (IC 3 & IC4) which provide the isolation between the circuit’s ‘driver’ section and the ‘power’ section, which is directly connected to the AC powerlines.

Each phototriac drives a power triac (TRI1 & TRI2). These two triacs are fitted in parallel and share the task of supplying the convector (RL): one triac supplies the positive half-cycle while the other triac supplies the negative half-cycle. The over-rating of the triacs (high rms current rating: 16 A) combined with their use in parallel and the alternating switching is aimed at reducing heating in the two components and reducing the bulk of the heatsinks employed. Experimentally, this solution gives rise to low heating of the heatsinks when the controller is powering a 2 kW-rated convector constantly (duty cycle D= 1).

The power consumed by the convector with controller is easy to calculate from the simple formula W= P× t× D where W =power consumed in watt-hours (Wh);P =rated convector power in watts (W);T =operating time of the convector/controller unit in hours (h); D =duty cycle set by potentiometer P1.

Example: for a duty cycle Dof 0.5 and an operating time of one hour, a 2 kW convector will consume 1 kWh.

 

Author : Gérard Guiheneuf  Copyright: Elektor

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Particularly LM317 Circuit With 12v Battery Charger Circuit

The LM317 is AN adjustable three terminal transformer that is capable of supply 1.2 to 37 volts with a secure 1.5A output current. The LM317 is prepackaged terribly} normal electronic transistor package that makes it very simple to mount in your circuits.

Schematic

Overview

The LM317 series of adjustable 3-terminal positive voltage regulators is capable of supply in more than 1.5A over a 1.2V to 37V output vary. they're exceptionally simple to use and need solely 2 external resistors to line the output voltage. Further, each line and cargo regulation square measure higher than normal mounted regulators.

In addition to higher performance than mounted regulators, the LM317 series offers full overload protection out there solely in IC's. enclosed on the chip square measure current limit, thermal overload protection and safe space protection.
The LM317 makes AN particularly easy adjustable change regulator, a programmable output regulator, or by connecting a set electrical device between the adjustment pin and output, the LM317 may be used as a preciseness current regulator. provides with electronic conclusion may be achieved by clamping the adjustment terminal to ground that programs the output to one.2V wherever most masses draw very little current.

Pinout

Options

Specifications

• Guaranteed 1% output voltage tolerance (LM317A)
• Guaranteed max. 0.01%/V line regulation (LM317A)
• Guaranteed max. 0.3% load regulation (LM117)
• Guaranteed 1.5A output current
• Adjustable output down to 1.2V
• Current limit constant with temperature
• P + Product Enhancement tested
• 80 dB ripple rejection
• Output is short-circuit protected

Output Formula

Circuit
Once you have learnt enough you can now put the LM317 into use and make the following circuit:

12v Battery Charger Circuit

The circuit may be accustomed charge 12V lead acid batteries.
Overview
Pin one of the LM317 IC is that the management pin that is employed to manage the charging voltage, Pin a pair of is that the output at that the charging voltage seems, Pin three is that the input to that the regulated DC offer is given.
The charging voltage and current is controlled by the electronic transistor (Q1), electrical device (R1) and POT (VR1). once the battery is 1st connected to the charging terminals, the present through R1 will increase. This successively will increase the present and voltage from LM317. once the battery is totally charged the charger reduces the charging current and also the battery are charged within the trickle charging mode.

Circuit Diagram

Notes

• The input voltage to the circuit should be a minimum of 3V more than the expected output voltage. luminous flux unit 317 dissipates around 3V throughout its operation. Here I used 18V DC because the input.
• The charging voltage may be set by victimization the POT (VR1).
• The luminous flux unit 317 should be mounted on a sink.
• All capacitors should be rated a minimum of 25V.
• You'll be able to use crocodilian clips for connecting the battery to the charger.

 

Source: StreamPowers

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Cheap DC Voltage Doubler

This is a cheap DC Voltage Doubler Circuit diagram, which requires a few components and will deliver 10V from a 5V power supply. If the oscillator must be built from a non-functional gate then is required 2 more components: R1 and C3.

The most important parameters of this voltage doubler circuit are given in the table below. Note that because of the IC tolerances these data may have some differences.

Cheap DC Voltage Doubler Circuit Diagram

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Mini Bench Supply

Every electronics engineer is familiar with the anxiety of the moment when power is first applied to a newly-built circuit, wondering whether hours of work are about to be destroyed in a puff of smoke. A high-quality power supply with an adjustable current limit function is an excellent aid to steadying the nerves. Unfortunately power supplies with good regulation performance are expensive and homebrew construction is not always straightforward. Many of the ‘laboratory power supplies’ currently on the market are low-cost units based on switching regulators which, although certainly capable of delivering high currents, have rather poor ripple performance. Large output capacitors (which, in the case of a fault, will discharge into your circuit) and voltage over-shoot are other problems.

The power supply described here is a simple unit, easily constructed from standard components. It is only suitable for small loads but otherwise has all the characteristics of its bigger brethren. Between 18 V and 24 V is applied to the input, for example from a laptop power supply. This avoids the need for an expensive transformer and accompanying smoothing. No negative supply is needed, but the output voltage is nevertheless adjustable down to 0 V.  A difficulty in the design of power supplies with current limiting is the shunt resistor needed to measure the output current, normally connected to a differential amplifier. Frequently in simple designs the amplifier is not powered from a regulated supply, which can lead to an unstable current regulation loop. This circuit avoids the difficulty by using a low-cost fixed voltage regulator to supply the feedback circuit with a stable voltage. This arrangement greatly simplifies current measurement and regulation.

Mini Bench Supply Circuit Diagram

To generate this intermediate supply volt-age we use an LM7815. Its output passes through R17, which measures the output current, to MOSFET T1 which is driven by the voltage regulation opamp IC1C. Here R11 and C4 determine the bandwidth of the control loop, preventing oscillation at high frequencies. R15 ensures that capacitive loads with low effective resistance do not make the control loop unstable. The negative feedback of AC components of the current via R12 and C5 makes the circuit reliable even with a large capacitor at its output, and negative feedback of the DC component is via the low-pass filter formed by R14 and C6. This ensures that the volt-age drop across R15 is correctly compensated for. C7 at the output provides a low impedance source for high-frequency loads, and R16 provides for the discharge of C17 when the set voltage is reduced with no load attached.

Current regulation is carried out by IC1D. Again to ensure stability, the bandwidth of the feedback loop is restricted by R19 and C8. If the voltage dropped across R17 exceeds the value set by P2, the current limit function comes into action and T2 begins to conduct. This in turn reduces the input voltage to the voltage regulation circuit until the desired current is reached. R7, R9 and C3 ensure that current regulation does not lead to output voltage over-shoots and that resonance does not occur with inductive loads.

The controls of the power supply are all voltage-based. This means, for example¸ that P1 and P2 can be replaced by digital-to-analogue converters or digital potentiometers so that the whole unit can be driven by a microcontroller. IC1B acts as a buffer to ensure that the dynamic characteristics of the circuit are not affected by the setting of P1. IC1A is used as a comparator whose out-put is used to drive two LEDs that indicate whether the supply is in voltage regulation or current regulation mode. If D2 lights the supply is in constant voltage mode; if D1 lights it is in constant current mode, for example if the output has been short-circuited. The power supply thus boasts all the features of a top-class bench supply.IC1A and its surrounding circuitry can be dispensed with if the mode indication is not wanted.

A type LM324 operational amplifier is suggested as, in contrast to many other similar devices, it operates reliably with input voltages down to 0 V. Other rail-to-rail opamps could equally well be used. The particular n-channel MOSFET devices used are not critical: a BUZ21, IRF540, IRF542 or 2SK1428 could be used for T1, for example, and a BS170 could be used in place of the 2N7002. The capacitors should all be rated for a voltage of 35 V or higher, and R15 and R17 must be at least 0.5 W types. The fixed voltage regulator and T1 must both be equipped with an adequate heatsink. If they are mounted on the same heatsink, they must be isolated from it as the tabs of the two devices are at different potentials.

Author : Alexander Mumm - Copyright : Elektor

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Fast Electronic Fuse

A fast electronic fuse designed to operate on 230V AC with an adjustable trip current. 

  Fast Electronic Fuse Circuit Diagram :

 

 Note :

When the current through the load exceeds a level determined by the position of the wiper on the 1k wire-wound pot, this circuit cuts off the load immediately. If S1 is open, the range is approximately 300-650 mA, and 0.8-2A when it is closed.

The key variable in the operation of the fuse is the voltage drop across the power resistor(s) which are connected in series with the load. This voltage drop is directly proportional to the current the load draws. When this current is low, the voltage across the resistors is also small and cannot trigger T1. At the same time the gate of T2 is fed from a little power supply built around a negative voltage regulator. T2 is conducting and the load is on.

If the current through the load then gets too high, so that the voltage created across the resistor(s) can trigger the gate of T1 through the 330R resistor and the pot: T1 starts to conduct, swiftly taking away all the current from the gate of T2. The voltage drop across T1 (MT1-MT2) will then be only 0.7 V and T2 will be firmly off. T1 stays this way all until the momentary (normally closed, "push-to-break") Reset push-button is pressed: this causes the current through T1 to drop below the hold level and forces this triac to turn off. Releasing the Reset button re-enables the current flow to and through the gate of T2, switching it on.

T1 must be a TIC225M, as this particular type has a very low trigger current. T2 is a snubberless BTA12-600CW which cannot be replaced with a 'normal' triac, but maybe with a BTA12-600BW which also can be used without a snubber circuit, but has a little less sensitive gate (not a problem in this design). If the gates of snubberless triacs are DC-controlled and they are switching AC, the DC to control the gates MUST be negative - flowing from the gate, hence the negative voltage regulator. (Snubberless is in fact a registered trade mark belonging to ST.)

The output AC voltage will be 1-5 volts below the input level, depending on the load. Varistors are 250V AC. Pay attention to the "reverse" polarities of the electrolytic capacitor and the diodes before the 7906.

DANGER! This circuit connects directly to 220-230V AC which can be lethal! Please do not attempt to build any of the circuits/projects unless you have the expertise, skill and concentration that will help you avoid an injury. Please see Disclaimer on this site.

Source : www.zen22142.zen.co.uk

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Energy-Efficient Backlight

The backlights used in some LCD panels are not exactly economical: typical current draws of 20 mA to 100 mA are common. Normally the current is determined by a series resistor, which leads to additional power losses. It is considerably more efficient, if a little more complex, to use a switching regulator IC. Alternatively, it is often the case that driving the LCD panel is a microcontroller, which we can press into service to provide regulation in software. Fortunately, the regulation does not need to be exceptionally precise.
At the heart of our circuit is T1, a p-channel MOSFET, which is driven by an inverted (active low) pulse-width modulated signal from the microcontroller. Component s D1, L1 and C1 form the remainder of the standard step-down switching regulator configuration. In the circuit diagram the LCD backlight is represented by two LEDs; the current flowing through these LEDs is measured by a shunt resistor, filtered, and finally amplified to a level suitable for input to the A/D converter in the microcontroller using an operational amplifier. R1 ensures that the transistor switches off completely when the microcontroller is reset (at which time all ports become inputs).
Energy-Efficient Backlight Circuit Diagram :

The circuit can be used with any microcontroller that can generate an inverted PWM signal at a frequency in the range 10 kHz to 100 kHz. We have developed a demonstration program and code module for the Atmel ATmega32 using GNU C. The source code can be downloaded from the Elektor website at http://www.elektor.com or from the author’s site at http://reweb.fh-wein-garten.de/elektor.
The program generates the PWM sig-nal at 31.25 kHz (if the processor clock is 8 MHz) on the OC2 output (PD2) of the ATmega32 microcontroller. The pulse width can be adjusted in 256 steps. If the gain of the operational amplifier is 25. 5 a current of 100 mA through the LEDs will correspond to a voltage of 2.55 V at the input to the A/D converter. The internal reference voltage of the ATmega32 is nominally 2.56 V, and so an LED cur-rent of 100 mA will lead to a ten-bit conversion result of 03FFh. It is sufficient to monitor only the top eight bits of this value, and depending on the error from the desired value, increment or decrement the pulse width of the PWM signal. This forms an integral controller.
As it stands, this solution can-not compete on simplicity with a series resistor. However, we can make some simplifications to the circuit by eliminating the regulation feedback loop. Dispense with the operational amplifier and surrounding circuitry, and have the software output a fixed PWM signal. This loses the ability of the circuit to compensate for part-to-part variation in the components and for temperature, but in practice such compensation is rarely necessary. The software also supports the simplified version of the circuit.

Author : Rainer Reusch - Copyright : Elektor

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Ground-free DVM Module Supply from 5 V

The majority of hand-held digital volt meters use an LCD screen and are powered from a nine volt battery. Inside is most probably an ICL7106 chip (or something compatible). This takes care of measuring the input and driving the LCD. This IC is very popular and can be found in other laboratory and homebrew equipment where it offers a simple solution for both measuring current/voltage and driving the display. So far so good, there is how-ever one feature of this device which needs careful consideration. The power supply to the chip (both the positive and negative connection) must not have any direct connection to either of the two measuring input terminals. It requires floating supplies. This is not a problem for battery powered equipment but needs more thought when the ICL7106 is fitted into mains powered equipment.

Ground-free DVM Module Supply from 5 V Circuit Diagram :

The simplest, most expensive solution is to use two independent power supplies in the equipment. A battery could also be used as an isolated supply but in a mains powered device it would seem a bit out of place and inconvenient.

In this case the term ‘floating supplies’ means that it is possible to have two separate DC levels. This level of isolation can be achieved with capacitors to separate the two DC supplies. Back in 2003 we published a circuit in the July/August edition of Elektor (circuit number 75) which used a NE555 IC. Unfortunately this design required a supply voltage upwards of 10 V. If the DVM module is fitted to equipment which only uses a 5 V supply (as is often the case) the circuit will not be of much use.The author has solved the problem by modifying the original circuit, using a hex Schmitt trigger inverter type 74HC14N instead of the NE555. One of the inverters generates a square wave of about 75 KHz. The remaining five inverters are wired in parallel to pro-vide more output drive current for the voltage multiplier stage.

DC isolation is provided by capacitors C2 and C3. A classic voltage multiplier configuration is made up of capacitors and diodes. The circuit generates an output of around 8.5 V at a load current of 1 mA. This is sufficient to power the DVM chip. The 5 V supply for the circuit must be stabilised.

The values of the input voltage divider resistors R2 and R3 are independent of the chip’s power supply and must be selected according to the desired measurement range.

Author : Heinz Kutzer  - Copyright : Elektor

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LM338 Power Supply +13.8V 5A

This ac to dc power supply can output 5A in continous operation and 12A peak current. This kind of dc power supplies uses a PCB so you can use two case types for IC1, TO-220 or TO-3. The regulation of this 12 volt power supply is made with TR1 ( multiturn ). IC1 must be placed on proper heatsink.

LM338 Power Supply Circuit Diagram :

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Ultra Low Drop Linear Regulator

The circuit is a MOSFET based linear voltage regulator with a voltage drop of as low as 60 mV at 1 ampere. Drop of a fewer millivolts is possible with better MOSFETs having lower  RDS(on)  resistance.

The circuit in Fig.1 uses 15V-0-15V secondary output from a step-down transformer and employs an n-channel MOSFET IRF540 to get the regulated 12V output from DC input, which could be as low as 12.06V. The gate drive voltage required for the MOSFET is generated using a voltage doubler circuit consisting of diodes D1 and D2 and capacitors C1 and C4. To turn the MOSFET fully on, the gate terminal should be around 10V above the source terminal which is connected to the output here. The voltage doubler feeds this voltage to the gate through resistor R1. Adjustable shunt regulator TL431 (IC2) is used here as an error amplifier, and it dynamically adjusts the gate voltage to maintain the regulation at the output.

Circuit Fig.1

With adequate heatsink for the MOSFET, the circuit can provide up to 3A output at slightly elevated minimum voltage drop. Trimpot VR1 in the circuit is used for fine adjustment of the output voltage. Combination of capacitor C5 and resistor R2 provides error-amplifier compensation.

The circuit is provided with a short-circuit crow-bar protection to guard the components against over stress during accidental short at the output. This crow-bar protection will work as follows: Under normal working conditions, the voltage across capacitor C3 will be 6.3V and diode D5 will be in the off state since it will be reverse-biased with the output voltage of 12V. However, during output short-circuit condition, the output will momentarily drop, causing D5 to conduct and the opto-triac MOC3011 (IC1) will get triggered, pulling down the gate voltage to ground, and thus limiting the output current. The circuit will remain latched in this state, and input voltage has to be switched off to reset the circuit.

Circuit Fig.2

The circuit shown in Fig.2 follows a similar scheme. It can be utilised when the regulator has to work from a DC rail in place of 15V-0-15V AC supply. The gate voltage here is generated using an LM555 charge pump circuit as follows:

When 555 output is low, capacitor C2 will get charged through diode D1 to the input voltage. In the next half cycle, when the 555 output goes high, capacitor C3 will get charged to almost double the input voltage. The rest of the circuit works in a similar fashion as the circuit of Fig. 1.

The above circuits will help reduce power-loss by allowing to keep input voltage range to the regulator low during initial design or even in existing circuits. This will keep the output regulated with relatively low input voltage compared to the conventional regulators.

The minimum voltage drop can be further reduced using low RDS(on) MOSFETs or by paralleling them.

Author :P.S .SINI - Copyright : EFY

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Simple Voltage Booster

Here is a simple circuit for boosting 12 V DC to 24 V DC .The circuit is designed straight forward and uses few components.With few modifications the circuit can be used to boost any voltages.

The transistor Q1 and Q2 (D1616)  essentially drives the primary of the transformer.The diodes rectifies the output of transformer to obtain a 24V DC at the output load(here a fan).The capacitors filter away noise and harmonics away from the output.

Simple Voltage Booster Circuit Diagram :

Notes.

• The component values are not very specific here.We can use any NPN power transistors like D1616,2N 3055,C2236,SL 100 etc for Q1 and Q2.
• The transformer can be any center tapped 5A transformer with a  7:1 winding ratio.
• The diodes can be 1N 914 ones.
• In fact you can easily assemble the circuit from the components in your electronics junk box.
• By experimenting on the tranformer winding you can get different boost ratios.
• For high current (around 5A)  games use 2N 3055 transistor or more powerful Darlington pairs for Q1 and Q2.

 

Source : circuitstoday.com/voltage-booster-circuit

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15-V 1-A Regulated Power Supply

The supply receives - 20 V from the rectifier/filter which is fed to the collector of the Darlington pnp pass transistor, a TIP105. The base drive to the TIP105 is supplied through resistor R5. The base of the TIP105 is driven from Vz terminal at pin 9, which is the anode of a 6.2-V zener diode that connects to the emitter of the uA723 output control transistor.

Circuit diagram :

15-V 1-A Regulated Power Supply Circuit Diagram

The method of providing the positive feedback required for foldback action is shown. This technique introduces positive feedback by increased current flow through resistors R1 and R2 under short-circuit conditions. This forward biases the base-emitter junction of the 2N2907 sensing transistor, which reduces base drive to the TIP105.

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Tracking Solar Panel

This small 12 V solar power source maintains its orientation towards the sun under control of a timer rather than the more  usual light-sensitive arrangement. All the  parts needed to build the project can be found in a well-stocked hardware shop or DIY store.

The axle is made from the core of a roller blind with two bearings. Suitable angle brackets are readily available to hold these  bearings. The axis of rotation is set vertically, and the whole thing is directly driven by a battery-powered rotisserie motor. This motor already includes a gearbox to give a slow rotation and is capable of turning in either direction, and so one could hardly ask for a more perfect device for the job.

The upper end of the roller blind axle  must be filed down to a suitable (generally square) cross section to allow it to be  driven by the rotisserie motor. Now to the electrical department to find a cheap electronic mains time switch. The switch must be programmable for at least four on-off cycles per day. For the solar panel itself any 12 V solar charger designed for car, camping or boat use is ideal. It should be at most 0.25 m2 in area as other-wise the force of the wind may be too great for the gears in the rotisserie motor’s gear-box to withstand. The angle of inclination of the module is fixed, and depends on the latitude at which it is installed.

Circuit diagram :

Tracking Solar Panel Circuit Diagram

The mains portion of the times witch and  the switching relay are not required and are removed. The remainder of the time-switch will act as a clock which causes the  axle to be rotated eight times during the  course of each day: each on-to-off or off-to-on transition of the clock will advance the  axle by 22.5 degrees from east to west via  south. The angle through which the roller blind axle turns is defined by its octagonal  shape: the corners operate a micro-switch  S1, which is fitted with an actuation lever.  The position of the micro switch must be set  carefully so that the switch is closed when  the lever is pushed aside by a corner and  open when between corners. Each time  the time-switch changes state IC2, a CMOS  4011 which contains four NAND gates,  switches the drive motor on via p channel MOSFET T3 for as long as necessary  until the micro-switch also changes state.  Reasonable settings for the time switch  have been found to be as follows: 7.30 am  on; 9.00 am off; 10.30 am on; 12 noon off;  2.00 pm on; 4.00 pm off; 6.00 pm on; and  9.00 pm off.

After eight moves the solar panel has rotated through a total of 180 degrees and points directly west. Counter IC1,  constructed from the two CMOS JK flip-flops in a 4027, detects the eighth clock  pulse and turns on relay Re1 via IC3. This in turn reverses the polarity of the power  to the motor and the panel starts to turn  back from west to east. When it reaches  its original position facing due east limit  micro-switch S2, actuated directly by the  solar panel, opens. The connected load  is also switched on and off by S2, which is  open during the night and closed during  the day. The author uses his solar panel to operate a small water pump. For this purpose  the output of the panel is regulated to 5 V  using a highly efficient switching regulator.  Alternatively, 12 V lighting could be powered from the panel, with no need for the  regulator.

Of course, both the control electronics and the time-switch need to be housed in a waterproof enclosure. Energy storage to  cover for the inevitable cloudy days can  be provided by a 12 V battery comprising ten 2800 mAh AA-size NiMH cells in a  suitable battery holder, which can be fit-ted inside an ordinary electrical junction  box. A 3000 mAh D cell is fitted in the battery compartment of the rotisserie motor,  wired in series with the 12 V battery and  also charged from the solar panel.

The motor and battery connections from the rotisserie motor are taken to the con-trol circuit using a four-core cable. The  rotisserie motor’s switch is removed. Resistor and capacitor values shown in the cir-cuit are not particularly critical, and other  similar types can be substituted for T1, T2  and T3. A Schottky diode should be used  for D3, which prevents current flow back  into the solar panel, in order to minimise  power losses. The 5 V regulator operates  at around 250 kHz and so a high-speed  switching diode is needed for D4. Using  an ordinary 1N4007 considerably reduces  the efficiency of the regulator and is there-fore not a good idea. A small toroidalcore inductor is used for L1.

 

Author : Manfred Schmidt-Labetzke - Copyright : Elektor

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2W Switching Power Supply

This is a small switching power supply, a Schmitt trigger oscillator is used to drive a switching transistor that supplies current to a small inductor. Energy is stored in the inductor while the transistor is on, and released into the load circuit when the transistor switches off.

Circuit diagram :

2W Switching Power Supply Circuit Diagram

The output voltage is dependent on the load resistance and is limited by a zener diode that stops the oscillator when the voltage reaches about 14 volts. Higher or lower voltages can be obtained by adjusting the voltage divider that feeds the zener diode. The efficiency is about 80% using a high Q inductor.

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12V Fan Directly on 230 V

This circuit idea is certainly not new, but when it comes to making a trade-off between using a small, short-circuit proof transformer or a capacitive voltage divider (directly from 230 V mains voltage) as the power supply for a fan, it can come in very handy. If forced cooling is an afterthought and the available options are limited then perhaps there is no other  choice. At low currents a capacitive divider requires less space than a small,  short-circuit proof transformer.

Circuit diagram :

12V Fan Directly on 230 V Circuit Diagram

R1 and R2 are added to limit the inrush current into power supply capacitor C2 when switching on. Because the maximum rated operating voltage of resistors on hand is often not known, we choose to have two resistors for the current limit. The same is true for the discharge resistors R3 and R4  for C1. If the circuit is connected to a mains  plug then it is not allowed that a dangerous voltage remains on the plug, hence R3 and R4.

Capacitor C1 determines the maximum current that can be supplied. Above that maximum the power supply acts as a current source. If the current is less then zener diode D1 limits the maximum voltage and dissipates the remainder of the power. It is best to choose the value of C1 based in the maximum expected current. As a rule of thumb, start with the mains voltage when calculating C1. The 12 V output voltage, the diode forward voltage drops in B1 and the voltage drop across R1 and R2 can be neglected for simplicity. The calculated value is then rounded to the nearest  E-12 value.

The impedance of the capacitor at 50 Hz is 1 / (2π50C). If, for example, we want to be able to supply 50 mA, then the required impedance is 4600 Ω (230 V/50 mA). The value for the capacitor is then 692 nF. This then becomes 680 nF when rounded. To compensate for mains voltage variations and the neglected voltage drops you could potentially choose the next higher E-12 value. You could also create the required capacitance with two smaller capacitors. This could also be necessary depending on the shape of the available space. It is best to choose for C1 a type of capacitor that has been designed for mains voltage applications (an X2 type, for example).

 

Author : Ton Giesberts - Copyright : Elektor

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Phantom Supply From Batteries

Professional (directional) microphones often require a phantom supply of 48 V. This is fed via the signal lines to the microphone and has to be of a high quality. A portable supply can be made with 32 AA-cells in series, but that isn’t very user friendly. This circuit requires just four AA-cells (or five rechargeable1.2 V cells). We decided to use a standard push-pull converter, which is easy to drive and which has a predictable output voltage. Another advantage is that no complex feedback mechanism is required. For the design of the circuit we start with the assumption that we have a fresh set of batteries.

We then induce a voltage in the secondary winding that is a bit higher than we need, so that we’ll still have a high enough voltage to drive the linear voltage regulator when the battery voltage starts to drop (refer to the circuit in Figure 1). T1 are T2 are turned on and off by an astable multivibrator. We’ve used a 4047 low-power multivibrator for this, which has been configured to run in an astable free-running mode. The complementary Q outputs have a guaranteed duty-cycle of 50%, thereby preventing a DC current from flowing through the transformer. The core could otherwise become saturated, which results in a short-circuit between 6V and ground.

 

Circuit diagram :

Phantom Supply From Batteries Circuit Diagram

 

This could be fatal for the FETs. The oscillator is set by R1/C1 to run at a frequency of about 80 kHz. R2/R3 and D1/D2 make T1 and T2 conduct a little later and turn off a little faster, guaranteeing a dead-time and avoiding a short-circuit situation. We measured the on-resistance of the BS170 and found it was only 0.5 Ω, which isn’t bad for this type of FET. You can of course use other FETs, as long as they have a low on-resistance. For the transformer we used a somewhat larger toroidal core with a high AL factor. This not only reduces the leakage inductance, but it also keeps the number of windings small. Our final choice was a TX25/15/10-3E5 made by Ferroxcube, which has dimensions of about 25x10 mm.

This makes the construction of the transformer a lot easier. The secondary winding is wound first: 77 turns of a 0.5 mm dia. enamelled copper wire (ECW). If you wind this carefully you’ll find that it fits on one layer and that 3 meters is more than enough. The best way to keep the two primary windings identical is to wind them at the same time. You should take two 30 cm lengths of 0.8 mm dia. ECW and wind these seven times round the core, on the opposite side to the secondary connections. The centre tap is made by connecting the inner two wires together. In this way we get two primary windings of seven turns each.

The output voltage of TR1 is rectified by a full-wave rectifier, which is made with fast diodes due to the high frequency involved. C4 suppresses the worst of the RF noise and this is followed by an extra filter (L1/C5/C6) that reduces the remaining ripple. The output provides a clean voltage to regulator IC2. It is best to use an LM317HV for the regulator, since it has been designed to cope with a higher voltage between the input and output. The LM317 that we used in our prototype worked all right, but it wouldn’t have been happy with a short at the output since the voltage drop would then be greater than the permitted 40 V.

If you ensure that a short cannot occur, through the use of the usual 6k81 resistors in the signal lines, then the current drawn per microphone will never exceed 14 mA and you can still use an ordinary LM317. D7 and D8 protect the LM317 from a short at the input. There is virtually no ripple to speak of. Any remaining noise lies above 160 kHz, and this won’t be a problem in most applications. The circuit can provide enough current to power three microphones at the same time (although that may depend on the types used). When the input voltage dropped to 5.1 V the current consumption was about 270 mA. The reference voltage sometimes deviates a little from its correct value. In that case you should adjust R4 to make the output voltage equal to 48 V. The equation for this is: R4 = (48–Vref ) / (Vref / R5+50µA). To minimise interference (remember that we’re dealing with a switched-mode supply) this circuit should be housed in an earthed metal enclosure.

 

Author :Ton Giesberts - Copyright : Elektor

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Desktop Power Supply

Useful for electronics hobbyists, this linear workbench power supply converts a high input voltage (12V) from the SMPS of a PC into low output voltage (1.25 to 9 volts). An adjustable three-pin voltage regulator chip LM317T (IC1) is used here to provide the required voltages. The LM317T regulator, in TO-220 pack, can handle current of up to 1 amp in practice.

Fig. 1 shows the circuit of the desktop power supply. Regulator IC LM317T is arranged in its standard application. Diode D1 guards against polarity reversal and capacitor C1 is an additional buffer. The green LED (LED1) indicates the status of the power input. Diode D2 prevents the output voltage from rising above the input voltage when a capacitive or inductive load is connected at the output. Similarly, capacitor C3 suppresses any residual ripple.

Circuit diagram :

Fig.1: Desktop Power Supply Circuit Diagram

Connect a standard digital voltmeter in parallel with the output leads to accurately set the desired voltage with the help of variable resistor VR1. You can also use your digital multimeter if the digital voltmeter is not available. Switch on S1 and set the required voltage through preset VR1 and read it on the digital voltmeter. Now the power supply is ready for use. 

 

Fig.2:Pin Configuration of  LM317

The circuit can be wired on a common PCB. Refer Fig. 2 for pin configuration of LM317 before soldering it on the PCB. After fabrication, enclose the circuit in a metallic cover as shown in Fig. 3. Then open the cabinet of your PC and connect the input line of the gadget to a free (hanging) four-pin drivepower connector of the SMPS carefully. 

Fig.3: Sugested power  supply box

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Simple Triple Power Supply

Inexpensive miniature transformers normally provide one or two secondary voltages, which is sufficient for generating a set of positive and negative supply volt-ages, such as are needed for operational amplifier circuits. But what can you do if you need an additional voltage that is higher than either of the supply voltages (such as a tuning voltage for a receiver?). This circuit shows a simple solution to this problem, and it certainly can be extended to suit other applications. Using a 2×15-V transformer, it generates positive 24-V and 12-V supply voltages and a negative 12-V supply voltage.

Circuit diagram :

Simple Triple Power Supply Circuit diagram

The little trick for generating the +24-V output consists of using IC1 to create a virtual ground. This is based on a well-known circuit with a voltage divider formed by two equal-valued resistors, which divide the voltage Ub across the rectifier from approximately 40 V down to 20 V. This Ub/2 potential is buffered by an opamp, which allows this virtual ground to drive a load. The present circuit uses the same principle, but instead of being divided by a factor of 2, the volt-age across the rectifier (approximately 40 V) is divided unequally by R1 and R2. The resulting potential, which is buffered by the opamp and the subsequent transistor output stage, lies approximately 15 V above the lower potential, and thus around 25 V below the upper potential. The three voltages are stabilised using standard 100-mA voltage regulators, as shown in the schematic.

The supply voltages for the opamp are also asymmetric. Thanks to the low cur-rent consumption, this can be managed using two Zener diodes.

You must bear in mind that the secondary voltage generated by an unloaded miniature transformer is significantly higher than its rated secondary voltage. The following results were obtained in a test circuit using a 1.6-VA transformer with two 15-V secondary windings: the positive and negative 12-V outputs could be loaded at around 10 mA each, and the 24-V output could be loaded with approximately 20 mA, all without any drop in any of the output voltages. For small circuits such as a 0(4)–20-mA instrumentation loop, this is fully adequate. For more complex circuits or switched loads, additional compensation may be necessary.

Author : Bernd Schädler - Copyright : Elektor

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Mains Failure Alarm

This circuit was designed to produce an audible alarm when the mains power is interrupted. Such an alarm is essential for anyone whose livelihood depends on keeping perishable foodstuffs in cold storage.

The circuit is powered by a 12-V mains adapter. LED D5 will light when the mains voltage is present. When the mains voltage disappears, so does the +12 V supply voltage, leaving the volt-age regulator IC1 and relay driver T1-T2 without power. The relay driver, by the way, is an energy-saving type, reducing the coil current to about 50% after a few seconds. Its operation and circuit dimensioning are discussed in the article ‘Relay Coil Energy Saver’.

Circuit diagram : 

Mains Failure Alarm Circuit Diagram

The value of the capacitor at the output of voltage regulator IC1 clearly points to a different use than the usual noise suppression. When the mains power disappears, Re1 is deenergised and the 0.22 F Gold-cap used in position C4 provides supply current to IC2. When the mains voltage is present, C4 is charged up to about 5.5 volts with IC1 acting as a 100-mA current limit and D10 preventing current flowing back into the regulator output when the mains voltage is gone. According to the Goldcap manufacturer, current limiting is not necessary during charging but it is included here for the security’s sake.

The CMOS 555 is configured in astable multivibrator mode here to save power, and so enable the audible alarm to sound as long as possible. Resistors R5 and R6 define a short ‘on’ time of just 10 ms. That is, however, sufficient to get a loud warning from the active buzzer. In case the pulses are too short, increase the value of R5 (at the expense of a higher average current drawn from the Goldcap).

Author : Myo Min – Copyright : Elektor

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Triple Power Supply

This low-cost, multipurpose power supply fulfils the requirements of almost all laboratory experiments. Nonetheless, it can be easily fabricated by hobbyists.

A single transformer is used to build this triple power supply. Regulator IC LM317 generates variable power supply of 1.25 to 20V, 1A. The dual ±12V, 1A power supply is generated  by regulators 7812 and 7912. Similarly, dual ±5V, 1A power supply is generated by regulators 7805 and 7905. ‘On’/‘off’ switches (S2 through S4) select the required power supply. Variable power supply is used to study the characteristics of devices. Fixed +5V power supply is used  for all digital, microprocessor and microcontroller experiments. Dual ±12V power supply is used for op-amp-based analogue circuit experiments.

Circuit diagram :

Fig. 1: Triple power supply Circuit Daigram

 

Fig. 2: Pin configurations of regulators

Fig. 1 shows the circuit of the triple power supply, while Fig. 2 shows the pin configuration of the regulators used in the circuit. Transformer X1 steps down the mains power to deliver the secondary output of 18V-0-18V. The transformer output is rectified by full-wave bridge rectifier BR1, filtered by capacitors C1, C2, C3, C7 and C8, and regulated by IC1 through IC5. Regulator IC1 (LM317) provides variable voltages (1.25 to 20V), while IC2 and IC4 provide regulated +12V and –12V, respectively.The output of IC2 is fed to regulator IC3 (7805), which pro-vides fixed +5V. Similarly, the output of IC4 is fed to regulator IC5 (7905), which provides fixed –5V. Capacitors C4 through C6, and C9 through C11, are used for further filtering of ripples in positive and negative regulated power supplies. LED1 glows to indicate that +5V is available, while LED2 indicates that –5V is available.

Switch S1 is used for mains ‘on’/ ‘off’. Using  switches S2 through S4, any of the three supplies can be  independently turned off when not required in a particular experiment. This reduces unnecessary power dissipation and increases the life and reliability of the power supply. Since the circuit uses three terminal regulators, only capacitors are required at the input and output. The use of few components makes the circuit very simple. The three terminal regulators have heat-sink provision to directly deliver 1A output current. To ensure  the maximum output, do not forget to use heat-sinks for the regulators.

Fig. 3: Proposed cabinet for power supply

The three-terminal regulators are almost non-destructible. These have inbuilt protection circuits including  the thermal shutdown protection. Even if there is overload or shorting of the output, the inbuilt overload protection  circuit will limit the current and slowly reduce the output voltage to zero. Similarly, if the temperature increases beyond a certain value due to excessive load and heat dissipation, the in-built thermal shutdown circuit will reduce  the output current and the output voltage (gradually) to zero. Thus complete  protection is provided to the circuitry. Assemble the circuit on a general-purpose PCB and enclose in a box as shown in Fig. 3.

The step-by-step procedure to build the triple power supply for the laboratory follows:

1. Collect all the components shown in the circuit diagram.
2. Connect switch S1, fuse, transformer and mains cord to the assembled PCB as well as the box.
3. Keep the multimeter in DC voltage range (more than 25V DC) and measure the DC voltage across capacitors C1 and C7 (1000 µF, 35V). This voltage should be around 18V×1.41=25  to  26V  DC. Check  both positive and negative voltages with respect to ground.
4. It is advisable to use three-wire mains cable and plug. If you are using any metallic box, earthing wire/pin of the mains plug should be soldered to the body of the metallic box using an earthing tag.
5. If the 18V-0-18V transformer is replaced with 15V-0-15V transformer , the output voltage of the variable supply using LM317 will be correspondingly lower.
6. Connect variable regulator LM317 to the circuit and check 1.25V to 20V output by varying the 2.2-kilo-ohm linear potentiometers.
7. Now connect ICs 7812, 7912, 7805 and 7905 to the circuit and check their output voltage.
8. Connect terminals, potmeter, switches and indicator LED on the front panel of the box and complete  the  connections. Close  the  box  by  us-ing screws.

Precaution. At the primary side of the transformer,  230V AC could give lethal shocks. So be careful not to touch this  part. EFY will not be responsible for any  resulting loss or harm to the user.

Author : Sandip Trivedi And P.D. Lele – Copyright : EFY

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