400W car power amplifier. Based on a push-pull converter with TL494 (KA7500) driver, 500W of power is enough for four TDA7294 integrated amplifiers. Three three-digit multimeters on front-panel shows actual battery voltage, temperature, and estimated output power.
This is a copy of very good and tested AVT2732 circuit with all the current and voltage protections included. Schematic and polish description – LINK. This converter is based on the TL494(KA7500) driver, it runs at 30KHz, and it controls two IRFP064N transistors. Unfortunately, those transistors have big gate capacitance and is necessary to use a emitter follower – in this case two BD139 and BD140 pairs. Rectifier diodes are the super fast FES16. At the end 4x 4700uF capacitors pack. Over-voltage protection take care of the power amplifier safety – driver will shut-down if voltage exceeds 15V on input (converter has no voltage stabilization). Under-voltage protection take care of the car battery discharge – driver will shut-down if voltage drops to 9V and below. Current protection take care of switching transistors and general security of whole circuit. This is a very nice, simple, and reliable solution – if switching transistors are more loaded, then we get higher voltage on IN+ of build in comparator. This is measured by simple circuit consist of 1N4148 diodes and RC (10K,10n) filter. On IN-, we can adjust compare voltage with PR1 potentiometer and if voltage on IN+ exceeds that adjusted one, driver will shut-down. Green diode means normal work, red diode means that one of protections has disabled the driver. To restart, switch off and then on supply or REMOTE voltage. Soft-start circuit allows to slowly start converter and charge a big capacitance at the output. Converter driver is powered from REMOTE line, and it drains not more than 50mA from that line.
Switching transformer based on a TX42 (TX42/13/26) 3C90 core. Transformer wound with a 0.7mm copper winding wire. Primary winding: 4 turns with 20 wires. Secondary wining: 11 turns with 6 wires. That configuration allows to get +-40V of idly voltage with 14,5V on input. I did not use any voltage stabilization, +-40V is a safe voltage for working TDA7294. While work, this voltage will drop to about +-30V which is perfect voltage for work with 4ohm impedance.
4 x TDA7294 chip in its typical application, see datasheet for more. Theoretically, output power of each one is 100W… I did some measurements and get 85W rms power from each one amplifier chip with 1% distortions. MUTE and ST-BY circuit modified – see fig.17 in datasheet – and permanently connected to +V using a 1N1418 diode. Chips are connected in pairs with ST-BY and MUTE lines, so they are controlled in pairs too: channels A + B and C + D. This is important because those channels can work in normal or bridged configuration – and it is good if they can enable/disable at the same time. You can find normal/bridge config jumpers next to the input signal goldpin connectors – you can bridge A + B and C + D channels. To do this, input signal connect only to the first channel (A or C), and in second channel (B or D) put two jumpers on a marked goldpins (“bridge A+B” or “bridge C+D”) – one jumper on a pins which previously was an input connectors, and one jumper on a neighbor pins which connect inverted signal from first channel to input of a second channel. Now both channels are working in bridge, don’t forget to connect speaker properly.
You can find additional low-pass filter on PCB, cut-off at about 80Hz. You can use it as you want, for example connect it before bridged channels to get a nice subwoofer power output. It’s supplied with symmetric voltage +12V/-12V provided from 12V zener diodes voltage limiter.
…description will continue soon… switch to polish and use translator if want to read more
Some poor movie recorded while first startup, (sound overdriven in the video-recorder mic)
DOWNLOAD – schematic, pcb top and bottom layer (for amplifier and multimeter) in PDF, HEX, BIN, and source BAS files for uC.