12V / 10A Switching Power Supply

This is the circuit diagram of 12V / 10A switching power supply. The circuit, shown in the schematic, provides 12 volts, at 10 amperes, maximum, using a discrete transistor regulator with an op-amp functioning as a comparator in the feedback circuit. The supply was constructed in 1984 and is variable frequency, as opposed to the pulse width modulator (PWM) controllers used today. The transformer used in this design diagram was for 110-120VAC home electric main, you should change the transformer which has 220V primary if your home electric installation use 220VAC.

There is no adjustable current limiter in this unit, although R1, R2, R3, Q2, R8, R9, C5 and Q4 set the current limit to approximately 10 amps. As you can see, the design is very similar to that of a linear power supply, except that L1, and D1 have been added, and U1 operates in a switching mode as a comparator with a small amount of hystersis. The switching frequency of this unit varies with the output current drawn by the load. This is an undesireable feature, which is why PWM regulators are used today. With a PWM regulator, the switching frequency is constant and will produce spurs only at known discrete frequencies rather than spurs at all frequencies. The Darlington-connected pass transistor block in the schematic is there twice (in parallel) for robustness. R4 in an internal trim-pot that can set the output voltage anywhere between 5 to 15 volts.

circuit source: http://michaelgellis.tripod.com/power4.html

The construction of this 12V / 10A switching power supply which already tested by the author: