Does anyone know how to calculate the input power by first boosting the voltage and then reducing it?

小太阳yy

Does anyone know how to calculate the input power by first boosting the voltage and then reducing it? [Copy link]

 

Does anyone know a circuit that first boosts the voltage and then steps it down, and how to calculate the input power based on the output power? Could you please give me some advice?

chunyang

You need to know the efficiency to calculate it, and efficiency involves many aspects, including design and device selection. If you don’t know the detailed parameters, you can’t calculate it. In engineering, testing is used to obtain it.

小太阳yy

chunyang posted on 2021-11-2 15:13 You need to know the efficiency to calculate it, and efficiency involves many aspects, including design and device selection. If you don’t know the detailed parameters, you can’t calculate it. The way to do it in engineering is to use test...

Is it just the power of the back end divided by the efficiency, that is, the front end? First step up, then step down, and then convert twice? Is that right?

chunyang

小太阳yy posted on 2021-11-2 17:00 Do we just divide the efficiency by the power of the back end, that is, the power of the front end? First step up, then step down, and then convert twice? Is that right, big guy?

Yes, the problem is that you can't know the efficiency parameters precisely in advance.

小太阳yy

chunyang posted on 2021-11-2 17:14 Yes, the problem is that you can't know the efficiency parameters accurately in advance.

I think I can just estimate it in advance.

chunyang

Xiaoyangyy posted on 2021-11-3 07:57 I think it is enough to estimate it in advance

If you use IC and the circuit strictly follows the device manual, you can make estimates based on the parameters in the manual.

maychang

Xiaoyangyy posted on 2021-11-3 07:57 I think it is enough to estimate it in advance

For this kind of thing, it is best to measure it in real life. Your "boost first then buck" output and input are both DC, so it is easy to measure the power, just use a multimeter.

小太阳yy

The product has not been made yet, so there is no way to test it.

小太阳yy

chunyang posted on 2021-11-3 14:53 If you use IC and the circuit is strictly in accordance with the device manual, you can make an estimate based on the parameters in the manual.

Yes, I think so too. I have another question. For a DCDC circuit, after I choose an inductor with a certain inductance value through calculation, for example, I find that an inductor of 5μH is required. Should I choose one higher than 5μH or lower than 5μH?

What parameters in the circuit are determined by the inductance value?

chunyang

Xiaoyangyy posted on 2021-11-3 18:03 Yes, I think so too. I have another question. For the DCDC circuit, after I choose an inductor with a certain inductance value through calculation, for example, I choose...

The calculated inductance is the bottom line, and the actual selection should be based on the standard series. The inductance value determines the energy storage capacity, and the energy required for the voltage conversion of the switching power supply is all provided by the energy storage inductor.

小太阳yy

Why is the maximum voltage of the switch tube in the buck-boost circuit the input voltage plus the load voltage? I don't understand this.

小太阳yy

chunyang posted on 2021-11-3 21:13 The calculated inductance is the bottom line, and the actual selection should be based on the standard series. The inductance value determines the energy storage capacity, the energy required for the voltage conversion of the switching power supply...

Why is the maximum voltage of the switch tube in the buck-boost circuit the input voltage plus the load voltage? I don't understand this.

chunyang

Xiaoyangyy posted on 2021-11-4 10:32 Why is the maximum voltage of the switch tube in the buck-boost circuit the input voltage plus the load voltage? I don’t understand this

Analyze the two processes of inductor charging and releasing energy, and then look at the voltage on both sides of the switch in the two processes.

maychang

Xiaoyangyy posted on 2021-11-4 10:31 Why is the maximum voltage of the switch tube in the buck-boost circuit the input voltage plus the load voltage? I don’t understand this

If you draw the positive and negative signs of the input voltage and the voltage across capacitor C, and then look at the voltage across switch S when it is disconnected, you will understand.

maychang

Xiaoyangyy posted on 2021-11-4 10:31 Why is the maximum voltage of the switch tube in the buck-boost circuit the input voltage plus the load voltage? I don’t understand this

"I don't understand this."

The + sign marked on the load R in the figure is in the wrong position.