Incandescent light bulb cleverly used as transformer circuit

When installing or repairing the DC circuit of the automatic motor control circuit, sometimes a suitable small power transformer cannot be found. In this case, the incandescent lamp transformer rectifier circuit as shown in the figure can be used. EL is an incandescent light bulb, RP is a potentiometer, and VD1~VD4 are connected to form a bridge rectifier. VD5 is the voltage stabilizing diode, and C1 is the filter capacitor. Take the required voltage from both ends of the bulb EL circuit potentiometer RP. Without affecting the brightness of the lighting lamp EL, by adjusting RP, an AC voltage of several volts to more than ten volts can be obtained at both ends of Q1 and Q2. After rectification by VD1~VD4, filtering by C1, and voltage stabilization by VD5, the voltage at A and B DC voltage is output at both ends. During production, proper selection of the bulb EL and potentiometer RP according to the output current and voltage is the key to this circuit. When the output DC voltage is not higher than 12V and the current is below 100mA, EL can be selected from 25 to 40W; RP is 3W, 100Ω. When the output current is 100~200mA, EL uses 60W. RP5W,300Ω.