How does BUCK output negative pressure?

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How does BUCK output negative pressure? [Copy link]

 

As shown in the figure, both BUCKs are used to obtain a negative pressure output.

The output voltage and ground at the output end are swapped.

But the circuit below also connects the negative voltage of the output to the original ground of the input.

The above diagram does not have this, what is the reason?

Can negative voltage be obtained by simply swapping the positions of the output voltage and ground at the output terminal?

Or does it need special treatment?

呜呼哀哉

The key to positive and negative voltage is who you are looking at. From the chip, it is actually positive voltage. From the chip, the input voltage of the chip is actually Vin+Vout. These are non-isolated and cannot be reversed.

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I found this connection method on the forum.

The ground on the input side does not move.

The negative voltage of the output is connected to the input voltage through a capacitor.

This connection method should have the same meaning as the second picture in the first post.

So the question becomes why there is no capacitor in the first picture.

What is the function of this capacitor connecting the input and output?

吾妻思萌

Voltage Voltage is a voltage difference. High potential and grounding are both negative voltage.

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Azuma Simeng published on 2022-11-15 20:40 Voltage Voltage is a voltage difference. High potential and grounding are both negative voltage~

Yes, looking at this picture, now I want to know what this C87 is for

okhxyyo

Has the landlord's problem been solved?

qwqwqw2088

You can refer to the specifications of the LM2576 and LM2596 for the connection method of generating negative pressure.

qwqwqw2088

TPS5430 negative voltage circuit

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okhxyyo posted on 2022-11-18 14:27 Has the original poster's problem been solved?

I can't solve it. Is there anyone who can tell me the function of this capacitor in the negative voltage connection method?

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qwqwqw2088 posted on 2022-11-18 14:51 TPS5430 negative voltage circuit

The negative voltage connection method can be found in the specification. Now I want to know the function of this capacitor connecting the power input and the negative voltage output.

qwqwqw2088

Placardo posted on 2022-11-20 20:21 The negative voltage connection method can be found in the specification book. Now I want to know the function of this capacitor connecting the power input and the negative voltage output

Slow start effect

The buck circuit cannot generate negative voltage. When connected in a Buck-Boost conversion structure, the output is negative relative to the ground to generate a negative voltage.

Buck chip is used as negative voltage circuit, the input capacitor capacity is larger than the general step-down circuit, and slow start is also required