Circuit Project Electronic

DC Converter 12V to 1.5V at 4A by 78S40
Saturday, August 8th, 2009

The 78S40 is a very old, but still useful power conversion chip. It contains a 1.25V reference, comparator, gating, output transistor, flyback diode and an uncommitted operational amplifier, which is not used here, and draws very little power. As the internal transistor and diode are good only for 1A maximum, I had to use external [...]

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Flyback Driver Circuit with 2N3055
Saturday, May 30th, 2009

This is probably the most well known flyback transformer driver circuit. It uses two 2N3055 power transistors in a push-pull oscillator configuration. The value of the resistors is not that critical. In fact you can even use a 1/2W for the 27 ohm resistor, but it may burn out if it is left to run [...]

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12V 50W AC-DC Power Supply
Sunday, May 24th, 2009

This is a simple low-cost 50W off-line switching power supply, which can be used for home projects or to learn operation of flyback converters. It can work over a universal AC line input range 90-264 VAC and provides a 12VDC output at more then 4A load. Line and load regulation is better then 0.5%. The [...]

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