What is the significance of connecting two capacitors in series?

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What is the significance of connecting two capacitors in series? [Copy link]

 

What is the significance of connecting two capacitors in series at the power input? The capacitance of these two capacitors is 102. Can't I use a 104? And the input is only 12V. If it is due to the withstand voltage, then the withstand voltage of the general chip capacitor is enough.

PowerAnts

Gen_X published on 2022-3-20 09:42 First of all, there is TVS, which means there may be sharp pulses here, so the peak voltage will exceed 12V, so two 102s are needed in series; another meaning is that one...

102 capacity, 0402 withstand voltage 100V, 0603 withstand voltage 1000V, not expensive!

A 500pF capacitor costs 1 cent, which is not expensive!

It's just for safety, no need to talk nonsense! I know this very well

In the early days of making 3-cell battery game consoles, the VBAT decoupling capacitors were all made of 2 16V capacitors in series

Why don't TVSs connect in series? The probability of a TVS short circuit is very, very low, and there will be no problem with a fuse.

Why do ceramic capacitors have to be connected in series? The inside of this thing is a thousand-layer cake, and defects cannot be tested during the production process. Short circuits are random. After a short circuit, the current may not blow the fuse, but the capacitor itself will become a fire source. Although PCB is flame retardant, if there is a fire source, the PCB will continue to burn.

maychang

"Both capacitors have a capacitance of 102. Can't I just use a 104?"

The capacitance of 104 is 100 times that of 102, not 2 times.

However, I don't understand why two capacitors are connected in series. I can only ask the original circuit author about this.

仙猫

When capacitors of the same capacity are connected in series, their capacity will be halved instead of doubled.

Polarized capacitors can be used in bipolar circuits. For example, if you want to connect a 1000μF speaker in series, non-polarized capacitors are too expensive, so you can use two polarized electrolytic capacitors in series to achieve this cheaply. As for why small capacitors are connected in series, it is obviously not for the purpose of reducing costs. I suspect that they were copied from somewhere wrong.

dcexpert

It can also increase the withstand voltage. For example, the withstand voltage of the capacitor is only 10V, which is not enough in a 12V circuit. After series connection, the withstand voltage is doubled (theoretically).

PowerAnts

EU toy safety requirements: In toys and equipment used by children, any single component short-circuited must not cause a large current. . . .

Gen_X

First, there is a TVS, which means there may be a sharp pulse here, so the peak voltage will exceed 12V, so two 102s are needed in series;

Another meaning is that a 500P capacitor is needed, but this nominal value may not be available or it may be very difficult to buy, so two 102s are connected in series to achieve this.

Gen_X

Learned: "102 capacity, 0402 withstand voltage 100V, 0603 withstand voltage 1000V"!

I had no idea that ceramic chips are so well made nowadays. In the past, you had to place separate orders for 40V ceramic chips for 0805.

But I really don't know where to buy a nominal capacitor like 500P, the key is that I have never heard of it! It's only a penny.

Fred_1977

I agree with the 8th floor's statement. First, the capacity problem, and second, the voltage resistance is always

仙猫

"EU toy safety requirements: In toys and equipment used by children, the short circuit of any single component must not cause a large current."
It makes sense, this is a good piece of knowledge!

PowerAnts

Gen_X posted on 2022-3-20 10:39 I learned: "102 capacity, 0402 withstand voltage 100V, 0603 withstand voltage 1000V"! Now the ceramic chip is so good, it's really amazing...

Kid! You are doing technology without understanding the cost. I feel sorry for your boss. . .

PowerAnts

230p, 250p, 260p, 280p, 310p, 400p, 420p, 960p, I haven't seen it! I don't know, I can find it on digikey and mouser

小太阳yy

My personal opinion:

First, the withstand voltage value must meet the requirements, the overvoltage situation must be considered, and some circuits will have corresponding withstand voltage tests, which are usually much higher than the actual application.

Second, if two capacitors are connected in series, short circuit can be prevented.

se7ens

The 2nd floor statement is correct.

Just for safety

If it is pressure-resistant, you don't have to worry about it.

In addition, your TVS is unidirectional, and it will burn out directly if the power supply is reversed.

led2015

We make switching power supplies. For the output part, I prefer to use different capacitors to repeatedly experiment and arrange them.

nathanzhang

1. Voltage resistance considerations; 2. Reliability considerations; Whether the 12V power supply is provided by a battery or an adapter, a short circuit on the input side is an unsafe factor.

Ming8686

If the pressure resistance is sufficient, reduce the types of materials and use two in series instead.