After a sudden power outage, there is a chance that the computer will not boot up when the power is restored.

HUhu00

After a sudden power outage, there is a chance that the computer will not boot up when the power is restored. [Copy link]

 

 

This is a 12V20A switching power supply. For example, it outputs normally when it is turned on for the first time, and it may be normal for many times. But it will not turn on after it is disconnected. The starting capacitor also has a voltage of 14V, and the optocoupler also has a voltage of 12V, but there is no output. The IC used is LD6599. Please help me find out where the problem is. I don't have a circuit diagram

HUhu00

Why can't I post pictures?

fxyc87

Check if the power is off too slowly.

HUhu00

fxyc87 posted on 2023-2-20 10:00 Check if the power is off too slowly,

How to adjust this? The dummy load and VCC capacitor have been adjusted, and the above situation will recur.

qwqwqw2088

It doesn't look like a new board.

Is the startup resistor value or VCC capacitor capacity offset?

tagetage

After the power suddenly cuts off - what suddenly cuts off? Is it the input power? What is the load at this time? Is it a pure resistive load or an inductive load? The original poster did not make it clear. Even the input power is 220VAC or 48V, etc., it is not clear.

HUhu00

qwqwqw2088 posted on 2023-2-20 10:21 It doesn't look like a newly made board. Is the startup resistor value or VCC capacitor capacity offset?

This is a returned board. This phenomenon occurs regardless of whether the startup resistor and VCC capacitor are increased or decreased.

HUhu00

tagetage posted on 2023-2-20 10:35 After the sudden disconnection - what is it that suddenly disconnects, is it the input power supply? What is the load at this time, is it a pure resistance or an inductive load, the original poster has no idea...

The input is 220V, that is, VCC has a 14V power supply, but the output end does not output 12V voltage, and this phenomenon occurs randomly and is difficult to simulate

tagetage

HUhu00 posted on 2023-2-20 10:44 Input 220V, that is, VCC has 14V power supply, but the output end does not output 12V voltage, and this phenomenon occurs randomly, it is difficult to simulate...

In this case, the input power supply may be cut off and then powered on again in a very short time. If yours is 12V, 20A, the output filter capacitor is very large. Before the output capacitor is fully discharged, the input end is powered on again, resulting in abnormal output.

You can try it by disconnecting the input power when the machine is in no-load state or in very light load state (for example, just connect an LED indicator), and then powering it on again after an interval ranging from 1 second to several tens of seconds to see if the fault state can be revealed.

HUhu00

tagetage posted on 2023-2-20 11:05 This situation may be that the input power supply is powered off and then powered on again in a very short time. You are 12V, 20A, the output filter capacitor is very large, and the output capacitor...

I have tried this. I loaded 0.1A, that is, after turning on the machine, I let it discharge naturally for 10 minutes (not necessarily 10 minutes), and it might appear. But yesterday I changed ES1D to F7, and changed 4.7 ohms to 0 ohms. I tried it all afternoon yesterday and it didn't appear. Then after one night, it appeared again when I turned it on in the morning.

tagetage

The L6599d you bought is a domestic compatible chip for about 2 yuan. You can buy a genuine ST product to replace it. You can buy genuine products from RS, degikey, etc.

HUhu00

tagetage posted on 2023-2-20 11:29 The L6599d you bought is a domestic compatible chip for about 2 yuan. You can buy a genuine ST product to replace it. Go to RS, degikey and other places to buy genuine products.

It is possible that you have purchased a fake product. I will ask the IC manufacturer to come and analyze the reason in a few days.

HUhu00

tagetage posted on 2023-2-20 11:29 The L6599d you bought is a domestic compatible chip for about 2 yuan. You can buy a genuine ST product to replace it. Go to RS, degikey and other places to buy genuine products.

I changed a 6599 that I used a long time ago to see if the same phenomenon occurs.

tagetage

HUhu00 posted on 2023-2-20 20:21 I changed to a 6599 that I used a long time ago, and try to see if the same phenomenon occurs

Ok, waiting for your result.

dabiaoke

LD6599 should be the same pintop as ST6599. The main startup requirements are: the LINE voltage on pin 7 is greater than 1.05V, VCC is greater than the startup voltage of 10V (check the manual for details). Also, the ICENSE voltage on pin 6 should be 0 before startup. If there is power but it does not start, check the voltages on these pins.

HUhu00

dabiaoke posted on 2023-2-20 22:13 LD6599 should be pintopin with ST6599. The main startup requirements are: the voltage of the LINE pin on pin 7 is greater than 1.05V, and VCC is greater than the startup voltage of 10V ( ...

I measured the voltage of 1.79V on pin 7, 14V on VCC, and 0.75V on pin 6.

HUhu00

This is the waveform tested by the oscilloscope. The frequency is not displayed. The frequency is 350MHZ. It is said that the frequency is also high. Can someone tell me how to modify it?