Series switching power supply for self-made CATV amplifier

The power supply system of cable TV is AC 60V centralized power supply. The power supply for CATV amplifiers usually uses a power transformer step-down or an isolated switching power supply. This article introduces a series switching power supply with low cost and nearly 90% efficiency. See the attached diagram for the circuit.

working principle:

Diode VD1 performs half-wave rectification, and the output DC voltage is about 84V after filtering by C1. VMOS tube VT1 is used as a switching adjustment tube, VT2 is a pulse width modulation tube, and VT5 is an error amplifier tube. VT3 and VT4 form short circuit and current limiting protection. After the power is turned on, VT1 obtains the bias voltage through R2 and R1 and is turned on. The current supplies power to the load through L and R6 and charges C3 at the same time. When VT1 is cut off, the magnetic energy of the inductor L is converted into electrical energy, and its polarity is left negative and right positive. The freewheeling diode VD2 is turned on, and the current continues to supply power to the load through the diode, so that the load receives smooth DC power. If the output voltage is too high for some reason, the conduction degree of VT5 will increase, and the conduction degree of VT2 will also increase, causing the pulse width of VT1 to decrease, causing the output voltage to drop. On the contrary, the output voltage will rise again, and finally the output voltage will be kept stable. When the current reaches 2A, due to the voltage drop of R6 of 0.6V, VT3 is turned on. At the same time, VT14 and VT2 are also saturated and turned on, which limits the VTI output current and protects VT1.

Component selection:

For switching tube VT1, select P-channel type 6P20E (6A/200V, a radiator is required). VT2 and VT3 use 2N5401 (0.6A/160V), VT4 and VT5 use 2SC2383 (1A/160V). R6 is 0.3Ω/2W, and the remaining resistors are 1/4W. VD1 uses 1N5403 (3A/200V).

C1 uses 100μF/160V. The voltage regulator tube CW1 is 20V and CW2 is 6V. VD2 is the ultra-fast recovery diode HER303 (3A/200V).

debug:

This circuit only needs the component data to be correct. If the welding is correct, no debugging is required except adjusting R9 to make the output voltage 24V.