This switching power supply uses discrete transistor regulator MJE2955 and 2N2905. and an op-amp CA3140T functioning as a comparator in the feedback section. It provides 12V output at maximum current 10 Ampere.
This switching power supply 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.
The power supply 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.
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