The size, withstand voltage and direction of capacitor, how to choose these parameters?

Capacitor size. For ceramic capacitors and tantalum capacitors, size is same as resistors, for small sizes, imperial system is used, 0201, 0402, 0603, 0805, and for large sizes, metric system is used. , such as 2520, 3525, etc. For cylindrical electrolytic capacitors, size is usually described as "diameter x height".

Therefore, when designing hardware, size of reserved capacitor should be as large as possible. If you reserve 6x11 position, usually largest one is 100uF 25V. It's no problem to change to a smaller one to save costs, but it's hard to change to a larger one. Capacitor manufacturers cannot produce 6x11 470uF 25V capacitors. The same problem should be paid attention to ceramic capacitors. For example, reserve 0805 capacitor. In general, maximum size can be pasted 22uF 6.3V. If you want a larger capacitance or a higher voltage, it is difficult to find materials.

↑Electrolytic capacitors of various sizes

↑Ceramic capacitors of various sizes

↑Tantalum capacitors of various sizes

The withstand voltage of capacitors mainly includes 4V, 6.3V, 10V, 16V, 20V, 25V, 35V and 50V in a weak current field. Capacitors of hundreds of volts are mainly used in strong electricity. The choice of withstand voltage value is very very important, if you choose wrong value, your life will be in danger.

What happens if a 25V capacitor is connected to a 50V power supply? A ceramic capacitor has a chance to hold it, or it can burn out and short-circuit it. Electrolytic capacitors don't hold up at all, but straight through and short circuit or just explode. The tantalum capacitor should not hold it, and it will burn out when fireworks cloud rises.

When choosing capacitors for hardware, be sure to consider maximum line voltage. It is usually used at half size, that is, value of capacitor's withstand voltage should be twice or more than mains voltage. For example, a capacitor on a 5V power supply should be 10V instead of 6.3V. Capacitor on a 20V power supply, choose a 50V capacitor instead of a 35V capacitor.

Based on experience, slightly smaller ceramic capacitors can be selected, as ceramic capacitors are better able to withstand high voltage. Tantalum capacitors must be selected strictly more than 2 times, because. tantalum capacitors break more easily. It is recommended to use more than 2 times electrolytic capacitor to avoid hidden dangers caused by supplier's poor quality control.

Capacitor Direction: Ceramic capacitors do not have positive and negative poles, while electrolytic capacitors and tantalum capacitors have positive and negative poles. If flipped over, it will break and catch fire or explode.

Unfortunately, both electrolytic capacitors and tantalum capacitors are symmetrical and can be soldered on either front or back. When designing equipment, positive and negative poles of electrolytic capacitors and tantalum capacitors must be clearly distinguished on circuit diagram and printed circuit board, and they cannot be confused. When fixing SMT, you should also be careful not to put it back in.

↑Electrolytic capacitor designation and ceramic capacitor designation

↑The marked electrolytic capacitor is negative pole

↑The marked electrolytic capacitor is negative pole

↑Tantalum capacitors are positively marked

The marked electrolytic capacitor is negative pole and marked tantalum capacitor is positive pole. Two opposite.