12V Switching Power Supply
12V Switching Power Supply Circuit
Here is AC DC 12V switching power supply design that uses a transformer as a source of DC voltage. The unregulated power supply is generated through a diode bridge to reach 40 volts via capacitor C2 and C3 components. t provides 12V output at maximum current 10 Ampere.
The 12V switching power supply circuit uses discrete regulator transistors and 2N2905 MJE2955. The use of IC CA3140T serves as a comparator in the feedback circuit with input from the current limiter circuit and a voltage regulator on the output of R4, which is in series with R6.
The power supply design is very similar to that of a linear power supply, except that L1, and D1 had been added, and U1 operates in a switching mode as a comparator with a small amount of hysteresis. The switching frequency of this unit varies with the output current drawn by the load. This is an undesirable feature, which is why PWM regulators are used today.
12V Switching Power Supply Schematic
12V Switching Power Supply Circuit
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. More info on 12V switching power supply.
