Switching power supply schematic

power_wong921

Switching power supply schematic [Copy link]

 

Hello everyone!

I have been studying the principles of switching power supplies recently. I searched the following picture on the Internet. I don't quite understand some of the notes written on it, mainly the last paragraph: When the voltage of coil L3 on C5 increases after being rectified by D6, it also shows that the voltage of L2 on the negative electrode of C3 is lower after being rectified by D4. When it is as low as the voltage value of the voltage regulator D3 (9V), D3 is turned on, causing the base of V1 to short-circuit to the ground, turning off V1, and finally reducing the output voltage. What is the current flow of L2 at this time? Thank you!

power_wong921

At the same time, could you please help me understand the general principle of this diagram and whether the original author explained it correctly?

power_wong921

Original link: uc3842 switching power supply circuit diagram_switching power supply wiring circuit diagram summary_weixin_39773447's blog-CSDN blog

maychang

[What is the current flow of L2 at this time? ]

After “turning off V1”, the electromotive force on L2 is negative at the top and positive at the bottom (the end with a point is negative), and the capacitor C3 is charged through the diode D4.

maychang

power_wong921 posted on 2023-8-31 19:34 At the same time, can you please help me look at the general principle of this diagram. Is the original author's explanation correct?

[Please help me understand the general principle of this diagram. Is the original author's explanation correct? ]

Roughly correct.

power_wong921

maychang posted on 2023-8-31 20:34 [What is the current flow of L2 at this time? ] After "turning off V1", the electromotive force on L2 is negative at the top and positive at the bottom (the end with a dot is negative...

Thank you! Is the current coming from L2 an alternating current? In this way, the current can first pass through capacitor C3 and then be rectified by D4

maychang

power_wong921 posted on 2023-9-1 08:44 Thank you! Is the current coming from L2 an alternating current? In this way, the current can first pass through capacitor C3 and then be rectified by D4

[Excuse me, is the current coming from L2 an alternating current? ]

The transformer cannot transmit direct current, so the voltage at both ends of L2 must be pure alternating current. That is to say, the area of the voltage waveform at both ends of L2 above the horizontal axis must be equal to the area of the voltage waveform below the horizontal axis.

power_wong921

maychang posted on 2023-9-1 09:08 [May I ask if the current coming from L2 is alternating current? ] The transformer cannot transmit direct current, and the two ends of L2 must be pure alternating current, that is, the voltage across L2...

grateful!

maychang

power_wong921 posted on 2023-9-1 09:33 Thank you!

[Recently I am studying the principles of switching power supplies]

This is a self-excited flyback switching power supply. The circuit looks simple, but it is not easy to design. Moreover, this circuit can only use bipolar power tubes (it is more troublesome to use MOS tubes), and now the mainstream of switching power supplies uses power MOS tubes, which are also externally excited (compared to self-excited) and use special control and drive chips. So don't worry too much about this self-excited circuit.

power_wong921

maychang posted on 2023-9-1 10:41 [Recently I have been studying the principles of switching power supplies] This is a self-excited flyback switching power supply. The circuit looks simple, but it is not easy to design. And this power supply...

Thank you! I mainly want to understand the circuit schematics. You are right. Many of our company's product circuits use special control and driver chips, such as boost, buck, and LLC. Sometimes I ask the hardware engineer for the schematics that I don't understand. Learning is also very scattered. I am mainly responsible for the software part, but I think it may be more beneficial to learn hardware knowledge and then write software. Just reading books and materials may not work. It may be better to start with your own hands.

MrCU204

Isn't this RCC? !

This circuit can be a toy or sold for money. It is said that some chargers are RCCs.