What is the reason for the sudden reduction of tantalum capacitor at the power input end?

lym1210

What is the reason for the sudden reduction of tantalum capacitor at the power input end? [Copy link]

 

I recently used the LM2596 chip to draw a power module, 20V DC input, connected a 25V100uF tantalum filter capacitor at the input end, connected to the load, the total current of the circuit was about 2A, and the capacitor suddenly burned out after half an hour. At first I thought it was because the withstand voltage was not enough, so I changed it to a 35V tantalum capacitor, but it still didn't work. Even the capacitor at the output end was burned out. I would like to ask the seniors what the reason is. Is it possible that the ripple voltage of the power supply is too high, causing the ripple current of the capacitor to be too large and burn out?

qwqwqw2088

Use electrolytic capacitors instead. Tantalum capacitors are too fragile. Also, try not to place them at the power input during design. The power supply directly charges the tantalum capacitor, which can easily cause overcurrent. The correct way is to place the tantalum capacitor at the end of the line, generally at the output end of the voltage regulator IC, or at the IC power pin as a decoupling.

wenyangzeng

Looking at the silk screen, it seems that the polarity of the capacitors are soldered in reverse.

qwqwqw2088

wenyangzeng posted on 2019-1-4 09:33 From the silkscreen image, it seems that the polarity of the capacitors is reversed.

Reverse soldering of components is a low-level mistake in assembly, and it is not just the bonus that will be deducted

dcexpert

Good tantalum capacitors are not easy to break, but there are many fakes now.

lym1210

wenyangzeng published on 2019-1-4 09:33 From the silk screen, it seems that the polarity of the capacitor is reversed.

The polarity is not reversed. I have replaced it with an electrolytic capacitor and it still works, but I am not sure if the electrolytic capacitor will explode. The total current of my circuit is nearly 3A. How should I choose the right electrolytic capacitor? I currently choose a 100uF50V one. Should I change to a larger one or connect two small ones in parallel?

dfwisdom

Under oscilloscope monitoring: 1. Ripple current 2. Overshoot current at power-on 3. Instantaneous voltage at power-on

wenyangzeng

lym1210 posted on 2019-1-4 10:01 The polarity is not reversed. I have now replaced it with an electrolytic capacitor and it still works, but I am not sure if the electrolytic capacitor will explode. The total current of my circuit is nearly 3A...

100uF/50V is enough for the input end, and 470uF can be used for the output end

maychang

"Is it possible that the ripple voltage of the power supply is too high, causing the ripple current of the capacitor to be too large and burn out?" This is exactly the reason.

maychang

lym1210 posted on 2019-1-4 10:01 The polarity is not reversed. I have now replaced it with an electrolytic capacitor. It still works, but I am not sure if the electrolytic capacitor will explode. The total current of my circuit is nearly 3A...

In switching power supplies, aluminum electrolytic capacitors are more suitable than tantalum capacitors. Aluminum electrolytic capacitors may also be damaged by excessive ripple current, but tantalum capacitors are more likely to be damaged by excessive ripple current.

qwqwqw2088

Another obvious drawback of tantalum capacitors is that the temperature cannot be too high during welding.

chunyang

Tantalum electrolytics cannot be used in situations with large ripples, at least tantalum electrolytics cannot be used alone as the main filter in this situation, otherwise the loss will be too large and cause the tantalum electrolytics to heat up and burn out. The correct way to use it is to use aluminum electrolytics or large-capacity aluminum electrolytics + small-capacity tantalum electrolytics.

PowerAnts

When doing design, you need to know more about devices and read more datasheets. Don't be a frog in a well. Under the conditions of limited space and relatively loose costs, the rational use of tantalum capacitors is the only choice. Taking Panasonic's 6TPF330M9L tantalum capacitor as an example, solid electrolytic capacitors must be several times larger in size to achieve its withstand voltage, capacity and ESR. Vicor module's tens of V output filter capacitors are also mainly tantalum capacitors.