Please tell me what will happen if the output capacitance is too large in a general DCDC step-down circuit?

kaka009

Please tell me what will happen if the output capacitance is too large in a general DCDC step-down circuit? [Copy link]

邀请：@chunyang   参与回复

A few days ago, I saw someone make a power board and test it. It is a 24V to 12V DCDC, and the output capacitors are two supercapacitors and two 1F capacitors. I don't know what the output waveform will look like, or if there will be any problems with this design.

Will it short circuit when turned on?

maychang

If the buck circuit is equipped with a soft-start circuit, there will be no danger of "short circuit", but the startup process may take a longer time.

wangerxian

Do you have a schematic? Post it and we'll study it.

qwqwqw2088

The output capacitors of the DCDC step-down circuit are two supercapacitors and two 1F capacitors?

Such a large capacitor

Because the original poster saw "I saw someone else made a power board and tested it there"

I haven't seen other people's circuit schematics.

Division is another circuit function

This feels impossible

qwqwqw2088

If the circuit has a specific circuit topology, or a chip circuit, you can output a 1F capacitor to simulate it.

led2015

Connecting two capacitors directly at the output can cause a momentary high current to flow through the capacitors, causing a short circuit.

chunyang

This depends on the specific circuit. Generally, this usage is to provide energy to the load for a period of time after the previous stage loses power. The soft start circuit is required to limit the current when power is turned on. The output voltage waveform of the power-on transient is a relatively slow and gradually rising curve.

zhaoyanhao

Teacher Chunyang is right. It is very likely that in order to cope with the requirements of power-off work, it is used as a battery for a short time. There are more stringent requirements on the overall power consumption to be less than a certain amount, including the instantaneous power consumption when powered on. In this case, current limiting soft start must be added to the input, and the means of current limiting and heating issues must be considered. More stringent requirements are also required for system startup time, so the soft start time must be considered again. Generally, the military requirements are relatively high. A capacitor of several thousand μF costs tens of thousands. If this capacitor of several F is really used in the military, then the cost must be ignored.

kaka009

qwqwqw2088 posted on 2023-7-13 19:03 The output capacitors of the DCDC buck circuit are two supercapacitors, two 1F capacitors? Such a large capacitor because the OP saw "seeing other...

I asked about it, and they said that two large 1F capacitors were placed on the output, and they said that the output waveform was too jumpy. I have used that capacitor before. I made a power supply before and used it to power the main module after a power outage.

kaka009

zhaoyanhao posted on 2023-7-14 09:28 Teacher chunyang is right. It is very likely that in order to cope with the requirements of power-off work, it can be used as a battery for a short period of time. There are also more stringent requirements for low overall power consumption...

Supercapacitors are not expensive, only a few dozen dollars. I have used them. It is definitely not possible to directly enlarge the capacitor. The load power consumption is relatively large. I have done the power failure backup power supply part, using MOS tube to control the switch, only supplying power to the CPU.