Beijing brand black and white TV switching regulated power supply

The picture shows a Beijing brand black and white TV switching regulated power supply. It is a typical example of a low-voltage switching regulated power supply. This power supply has three DC outputs, namely 18V, 28V, and 12V. Among them, 28V is directly output by bridge rectifier; 12V is output by 28V after being regulated by a switching regulator; 18V is output by a half-wave rectifier and filter circuit composed of VD612 and C612. VZ60l is a switching power adjustment tube. VT601~VT603, R601, C60l, etc. form a self-excited resonant oscillator. This power supply is a pulse width modulation switching regulated power supply. When the 12V voltage increases for some reason, the base potential of the error amplifier tube VT604 increases accordingly. The collector potential drops, the base potential of VT603 also drops, and the output pulse width of the switching regulator tube VT60l narrows, causing the increased voltage to drop again. When the 12V output voltage decreases, perform the opposite adjustment according to the same process as above, so that the dropped voltage rises again, that is, the stability of the output voltage is maintained. Diode VD605 plays a holding role. L601 and L602 are both energy storage inductors and form pulse filters with C606 and C607 respectively, reducing the output ripple to less than 15mV. The main technical indicators of this power supply are as follows: Voltage stabilization range: 150~270V; Efficiency: (66±2)%; Internal resistance: 160±40mΩ; Output ripple: (15±5)mV; Output voltage: 12V, 18V, 28V; Protection performance: 12V overload capacity is greater than 2A, open circuit and short circuit are allowed.