A simple positive and negative power supply circuit

The positive and negative power supplies in the attached figure are circuits composed of two independent power supplies but sharing a winding of a transformer. The positive and negative power supplies are named B+ and c-. The c-power supply is a negative power supply. Its output can be adjusted to 0-6.2V (no output current is provided); the B+ power supply is a positive power supply, and its output voltage is +90V. The following discusses its circuit composition separately.

1. C-power supply C-power supply is a negative power supply, i.e., a lean output. As shown in the attached figure, the C-power supply is filtered by two filter networks, R1, C1, and R2, C2, rectified by diode D1. Resistor R1 reduces voltage and limits current to ensure that the voltage regulator D2 (6.2V) works normally. A potentiometer RP is connected in parallel to the output end of the power supply. By adjusting RP, an adjustable output voltage (0-6.2V) can be obtained.

2. B+ power supply B+ power supply is the positive power supply, that is, the positive output. When working, it is rectified by diode D3, filtered by inductor L1, capacitor C3, and CA.

Output positive voltage from B+ terminal. Different values ​​(0.5～2.5kΩ, 5～18kΩ) can be selected for R3 and R4 in the circuit. You can output the output voltage you need from B+ and D+ terminals. Capacitor C5 is a bypass capacitor for D+ terminal.

Now let's introduce the functions of R5 and R6 in the B+ power supply. In the B+ power supply, because the output voltage of B+ is relatively high, an electrolytic capacitor is added to the right end of R3 for filtering. The withstand voltage of the capacitor should be 100V. Since it is difficult to obtain an electrolytic capacitor with a withstand voltage of 100V, two 100μF/50V electrolytic capacitors are used in series to replace a single 50μF/100V electrolytic capacitor. Resistors R5 and R6 are connected in parallel with C3 and C4 respectively. The purpose is to balance the withstand voltage of C3 and C4.

The filter inductor L1 is replaced by the primary coil of the audio output transformer of a tube radio to ensure the inductance required for B+ power supply filtering.

The input AC power supply of the two power groups C- and B+ uses the same 115V AC power supply transformer T1. Transformer T1 is a 115V/6V power transformer, and the primary and secondary of T1 are used in reverse.

Therefore, when the power supply is working, a 6V AC voltage should be added to the input end of transformer T1 so that the circuit can work normally. When making it, wind a 220V/115V step-down transformer to replace T1 in the figure, and the circuit can work normally.

If the C- and B+ power supplies are required to provide a certain power output, the secondary coil of the transformer should be wound with thicker wires. At this time, the resistance values ​​of the resistor R2 and the RP potentiometer in the C- power supply should be greatly reduced; the resistance values ​​of R3 and R4 should also be adjusted accordingly for the B+ power supply; the inductor L should be rewound (with thicker wires), etc.

If C- and B+ are required to have a regulated output, relevant voltage stabilization circuits should be added. In short, when designing a power supply, relevant functional circuits should be added after rectification and filtering according to the needs, so that the power supply can meet the required application requirements.