12W Stereo Amplifier TDA1521 / TDA1521Q

This is a stereo audio amplifier circuit that provides 12W output power on each audio channel. This simple circuit is built on a single integrated circuit of TDA1521 / TDA1521Q, and only supported by few external components.

12W Stereo Amplifier Circuit Diagram

TDA1521/TDA1521Q is a dual high-fidelity audio amplifier encapsulated in a plastic 9-leads. The device is specially designed for power supply applications (eg, stereo TV and radio).

TDA1521/TDA1521Q features: Requires very few external components Low offset voltage between output and ground Input muted during power-on and off (no switch-on or switch-off clicks) Hi-fi according to IEC 268 and DIN 45500 Excellent gain balance between channels Short-circuit-proof Thermally protected This hi-fi stereo power amplifier is designed for mains fed applications. The circuit is designed for both symmetrical and asymmetrical power supply systems. An output power of 2 x 12 watts (THD = 0,5%) can be delivered into an 8 W load with a symmetrical power supply of ± 16 V.

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LM3410 LED Driver

The LM3410 IC is a constant current LED driver useful in either boost con-verter or SEPIC design applications. A SEPIC (Single Ended Primary Induct-ance Conver ter) design allows the power supply’s output voltage to be set above, below or equal to its input voltage. In this application the chip is configured as a boost-converter (i.e. the output voltage is greater than the input voltage).

LM3410 LED Driver Circuit Diagram

The LM3410 is available in two fixed-frequency variants. Using either the 525 kHz or 1.6 MHz clock version it is possi-ble to build a ver y compact LED driver. The output stage can supply up to 2.8 A, allowing several high-power LEDs to be driven from a rechargeable Lithium cell or several 1.5 V bat-teries. The chip also features a dimmer input giving simple PWM brightness control.Output current is defined by an external shunt resistor. To keep losses low the LM3410 uses an internal voltage reference of just 190 mV.

Power dissipation in the shunt resistor is therefore low. Using the desired value of LED current the value and power dissipation of the shunt resistor is given by:
R_Shunt = 0.19 V/I_LED
P_Shunt = 0.19 V*I_LED

A 10 µH coil (L1) will be suf ficient for most applications providing it has a suitable satu-ration current rating. The Input and output capacitors should be 10 µF ceramic t ypes with a low value of E SR . Many distributor s including Farnell stock these component s. The Diode should beaSchottky type (as in all switching regulators). The author has developed a PCB for this design; the corresponding Eagle files can be freely downloaded from www.elektor.com/090850. In sum-mar y the most important features of the LM3410 are:

• Integrated 2.8 A MOSFET driver.
• Input voltage range from 2.7 V to 5.5 V.
• Capability to drive up to six series connected LEDs (maximum output 24 V).
• Up to 88 % efficiency.
• Available is 525 kHz and 1.6 MHz versions.
• Allows both boost and SEPIC designs.
• Available in 5 pin SOT23 or 6 pin LLP outline.

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Water Alarm Schematic

The LM1830 fluid detector IC from National Semiconduc tor is designed to be able to detect the presence of fluids using a probe. This chip requires a relatively high supply voltage and is not the most frugal power consumer. It is also quite specialised so unless you are buying in bulk the one-off price is not cheap.

An alternative circuit show n her e uses a standard CMOS IC type 74HC14. It has the advantage of operating with a 3 V supply and consumes less than 1 µA when the alarm is not sounding, this makes it ideal for use with batteries.

Water Alarm Schematic Circuit Diagram

The 74HC14 has six inverters with hysteresis on their input switching thresholds. A capacitor (C1) and a feedback resistor (R1) is all that’s necessary to make an inverter into a square wave signal generator.

In the water alarm circuit the feedback resistor consists of R1 and the water sensor in series. R1 prevents any possibility of short-circuit between the inverter’s input and out-put. Resistor R2 defines the inverter’s input signal level when the sensor is not in water. Any open-circuit (floating) input can cause the inverter to oscillate and draw more current.The remaining inverters in the package (IC1.B to IC1.F) drive the piezo buzzer to produce an alarm signal. Capacitor C2 ensures that no DC current flows when the circuit is in monitoring mode (with the alarm silent) this helps reduce the supply current.

A micro-switch can also be substituted for the water sensor to make the circuit a more general purpose alarm generator.

Author: Roland Heimann - Copyright: Elektor

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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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Multitasking Pins

It’s entirely logical that low-cost miniature microcontrollers have fewer ‘legs’ than their bigger brothers and sisters – some-times too few. The author has given some consideration to how to economise on pins, making them do the work of several. It occurred that one could exploit the high-impedance feature of a tri-state output. In this way the signal produced by the high-impedance state could be used for example as a CS signal of two ICs or else as a RD/WR signal.

Multitasking Pins  Schematic

All we need are two op-amps or comparators sharing a single operating voltage of 5 V and outputs capable of reaching full Low and High levels in 5-V operation (preferably types with rail-to-rail outputs). Suitable examples to use are the LM393 or LM311.The resistances in the voltage dividers in this circuit are uniformly 10 kilohms.

Consequently input A lies at half the operating voltage (2.5 V), assuming nothing is connected to the input or the microcontroller pin connected is at high impedance. The non-inverting input of IC1A lies at two-thirds and the inverting input of IC1B at one third of the operating voltage, so that in both cases the outputs are set at High state. If the microcontroller pin at input A becomes Low, the output of IC1B becomes Low and that of IC1A goes High. If A is High, everything is reversed.

Author : Roland Plisch - Copyright: Elektor

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