How to eliminate the current in IO after power failure

曹伟1993

How to eliminate the current in IO after power failure [Copy link]

After the microcontroller is powered off, the LED light connected to the IO port will still light up for a while (the anode of the LED light is connected to 3.3V, and the cathode is connected to the IO port).

dcexpert

Is this a large capacitor in the system?

qwqwqw2088

First cut off the 3.3V power to see if there is still a delay

Then cut off the power supply to the microcontroller and analyze the problem.

maychang

It is estimated that there is a large capacitor in the 3.3V circuit, and the large capacitor has not been fully discharged.

曹伟1993

qwqwqw2088 posted on 2020-6-16 11:25 First cut off the 3.3V power to see if there is still a delay, then cut off the power supply to the microcontroller and analyze the problem

First, I cut off the external power supply and only left 3.3V power supply. There was a delay. Later, I found that the capacitance of one of the capacitors was increased when it was handed over to the outside for welding, which caused the capacitor to discharge for too long after power failure.

曹伟1993

dcexpert posted on 2020-6-16 11:11 This is a large capacitor in the system

Yes, the original design did not have a capacitor, but when I gave it to someone else to solder, I couldn't find one, so I replaced it with a larger capacitor. After the power was turned off, the discharge was slow.

dcexpert

Cao Wei 1993 posted on 2020-6-16 15:19 Yes, yes, the original design did not have a capacitor, but when I gave it to someone else to solder, I couldn't find one, so I privately replaced it with a larger capacitor...

If you keep the large capacitor, you can detect power failure

huo_hu

I also want to talk about power-off detection. You have to systematically analyze how your system handles low-voltage conditions, and how to solve the problem if the power supply voltage is really low.

The low voltage, reset, and watchdog of some microcontrollers can be linked together, depending on how you want to handle it.