Q4 burns after a while of power on

anwinn

Q4 burns after a while of power on [Copy link]

 

After power on, the 24v and 12v power indicator lights flash frequently, and Q4 burns out after a while. Please help analyze the cause? Please give me some advice.

maychang

The picture is too blurry, and I can't really see where Q4 is. I'll tidy up the picture and post it again.

chunyang

The picture is totally unclear!

anwinn

Rookie, so stupid

chunyang

Is the load of Q4 a piezoelectric ceramic transformer? If so, first check the excitation signal, pay attention to adjusting R114 and check the overcurrent protection circuit.

anwinn

chunyang posted on 2018-6-22 13:17 Is the load of Q4 a piezoelectric ceramic transformer? If so, first check the excitation signal, pay attention to adjusting R114 and check the overcurrent protection circuit.

Not sure, it is the kind of winding transformer. I only turned on the 220 AC power switch, and the machine burned out after a while before I pressed the start button. Thank you.

chunyang

anwinn posted on 2018-6-22 13:50 Not sure, it's the kind of coil transformer. Just turn on the AC 220 power switch, the machine hasn't been started yet, and it burned out in a while. Thank you.

The symbol of the coil transformer cannot be drawn as shown in the figure. Disconnect the transformer or remove Q4 to measure the drive waveform.

maychang

anwinn posted on 2018-6-22 12:22 Rookie, too stupid

There is a sentence in Japanese in the picture. From the electrical schematic, this is a non-isolated converter that gets +400V from +24V. The circuit uses four power supplies: +5V (Vcc), +12V, -12V, +24V. The driver Q4 uses a resistor R106 to pull up, and a TL084 is used for feedback control. The transformer does not have the same-name terminal marked, so it is not certain whether the main circuit is forward or flyback. To get +400V from +24V, most likely a flyback should be used, but from the circuit including D39, the circuit is forward.

maychang

anwinn posted on 2018-6-22 12:22 Newbie, too stupid

Judging from the use of discrete transistors and pull-up resistors for the driver, and TL084 as feedback control, and no dedicated control chip for the switching power supply, this is a very old circuit design (there was no dedicated control chip era).

maychang

anwinn posted on 2018-6-22 12:22 Rookie, too stupid

I guess the OP did not spend time learning the principles of switching power supplies and practical application circuits, but found a circuit on the Internet, gathered the components, and soldered them. Then even the power MOS tube and the transformer started to smoke.

maychang

anwinn posted on 2018-6-22 12:22 Rookie, too stupid

I don't know if the original poster wants to use this circuit to learn about switching power supplies, or if the boss asked him to get a 400V DC power supply. If it's the former, I advise the original poster to give up this circuit and start learning from the working principle of switching power supplies. If it's the latter, I also advise the original poster to give up this old circuit, stop bothering with it, and redesign it with modern devices.

anwinn

chunyang posted on 2018-6-22 15:08 The symbol of the coil transformer cannot be drawn as shown in the figure. Disconnect the transformer or remove Q4 to measure the drive waveform.

Thank you for your guidance. I will try it later.

anwinn

maychang posted on 2018-6-22 16:12 I guess the OP did not spend time learning the principle of switching power supply and practical application circuit, but found a circuit on the Internet, gathered the components and soldered them. ...

I really don't understand. This is indeed a Japanese design from at least ten years ago. It is a small part of a small device circuit board. It is broken, so I want to take a look.

maychang

anwinn posted on 2018-6-22 17:25 I really don't understand. This is indeed a Japanese design from at least ten years ago. It is a small part of a small device circuit board. It is broken and I want to take a look.

Ten years ago? I'm afraid it's more than that, at least twenty years. If you just want to "take a look", then forget it. It takes a lot of effort to figure out the cause of the burn, and you don't learn much knowledge, not to mention that it is a damaged circuit board. It is very difficult to figure out the cause of the burn.

风吹过北纬

666666

学精电子

Look at the output waveform of Q5. Is it the same as the original model when Q4 is replaced?

PowerAnts

Xuejing Electronics published on 2018-7-19 15:52 Take a look at the output waveform of Q5. Is Q4 the same as the original model when it is replaced?

It is normal if it burns, and it is abnormal if it does not burn! High-voltage and low-current forward-pulse circuits are originally designed by people who do not understand forward-pulse circuits. Limited by the inductance, high-voltage and low-current forward-pulse circuits are basically in DCM, and the ringing amplitude will be frighteningly large. In the picture of the original poster, a large resistor is connected in series with the inductor for damping. It can be seen that the designer is very troubled by this matter, but the goal has been set: to make a forward-pulse circuit. . . During the heyday of power controllers, the Japanese stubbornly believed that RCC could be used in the home appliance industry for 10,000 years, and they devoted themselves to making RCC to the extreme (now anyone who still uses RCC will be criticized). Today, there are few power controllers in Japan, and Europe and the United States have dominated the market.