Help! Help! Dual buck power input, one of the MOS tubes always burns out!

czh778439397

Help! Help! Dual buck power input, one of the MOS tubes always burns out! [Copy link]

 

When Q4 is turned off, Q3 can work normally. When Q3 is turned off, Q4 can work normally. However, when Q4 works normally, Q3 will burn out!

czh778439397

The frequencies of pwm1 and pwm2 are both 20kHz, and the main parameters of MOS tube IRF4905 are: (Vdss=-55V, Rds(on)=0.02ohm, Id=-74A)

maychang

"When Q4 is turned on and working normally, Q3 will burn out!" Who designed this circuit? Calculate it yourself: when Q4 is turned on (that is, the negative end of the 18V power supply is connected to the positive end of the 24V power supply), what is the voltage between the gate and source of Q3?

xunke

However, the driver of PWM1 needs to be changed.

czh778439397

maychang posted on 2018-6-17 14:13 "When Q4 is turned on and working normally, Q3 will burn out!" Who designed this circuit? Calculate it yourself: When Q4 is turned on (that is, the 18V power supply is negative...

It seems that this is how it is broken down! Is there any Vgs<-42v? I have seen that Vgs is basically 20v!

maychang

czh778439397 posted on 2018-6-17 16:08 It seems that this is how it was broken down! Is there any Vgs

Is there any Vgs<-42v? I haven't seen it.

czh778439397

maychang posted on 2018-6-17 14:13 "When Q4 is turned on and working normally, Q3 will burn out!" Who designed this circuit? Calculate it yourself: When Q4 is turned on (that is, the 18V power supply is negative...

Or how can it be improved?

maychang

czh778439397 posted on 2018-6-17 16:08 It seems that this is how it was broken down! Is there Vgs?

I don't understand why two Buck circuits are used, and they are connected in series at the freewheeling diode. In addition to the complex circuit, the two Bucks will also restrain each other.

maychang

czh778439397 Published on 2018-6-17 16:29 Or how can it be improved?

"Or how can it be improved?" Two DC power supplies, one 24V and one 18V, why must two Buck circuits be used? Can't two batteries (42V) be connected in series and use a Buck circuit to step down the voltage (and also stabilize the output voltage at the same time)?

czh778439397

maychang posted on 2018-6-17 16:41 "Or how can it be improved?" Two DC power supplies, one 24V and one 18V, why must two Buck circuits be used? Can't two...

Because the two power supplies use 18V solar cells and 24V after the mains is stepped down and rectified, the circuit topology is a dual buck power input

czh778439397

xunke posted on 2018-6-17 16:06 However, the driver of PWM1 needs to be changed.

You can't directly connect the negative pole of 18V there, because the upper and lower MOS tube drive circuits are output by the same microcontroller. If you connect it to the negative pole of 18V, it is equivalent to connecting it to the negative pole of 24V.

maychang

czh778439397 posted on 2018-6-17 20:24 Because the two power supplies use 18V solar cells and 24V after the mains is stepped down and rectified, the circuit topology uses dual buck power input

The author seems to want to use the 24V after the mains is stepped down when the solar cells are not illuminated. Two Buck circuits must be used, and the DC output ends of the two Buck circuits should be connected in parallel, that is, two inductors should be used. Since the mains is used, it is better to directly use 220V rectification and filtering and then use a flyback circuit (with a high-frequency transformer) to directly generate the DC voltage required by the author.

maychang

czh778439397 Published on 2018-6-17 20:26 The negative pole of 18V cannot be directly connected there, because the upper and lower MOS tube driving circuits are output by the same microcontroller. If it is connected to the negative pole of 18V, it would be quite...

To solve the level problem of the upper and lower tubes being driven by the same signal source, you can consider using optocoupler isolation.

czh778439397

maychang posted on 2018-6-17 20:32 The author seems to want to use the 24V stepped-down mains voltage when there is no light on the solar cell. Two Buck circuits must be used, and they should also be...

I just want to achieve Vo=Vin1*D1+Vin2*D2, and when the solar energy decreases, the mains output will automatically increase, and when the solar energy increases, the mains output will automatically decrease, keeping the total output voltage Vo unchanged. I now have the 24V mains, sampling circuit, feedback circuit, and single-chip program automatic control. The only thing missing is the MOS tube drive circuit here.

czh778439397

maychang posted on 2018-6-17 20:35 To solve the level problem of the upper and lower tubes driven by the same signal source, you can consider using optocoupler isolation.

The upper and lower tubes are two different PWM signals sent by the same microcontroller. Can the upper tube be driven by a MOS tube with a step-down voltage?

maychang

czh778439397 Published on 2018-6-17 21:19 The upper and lower tubes are two different PWM signals sent by the same microcontroller. Can the upper tube be driven by a MOS tube with a step-down voltage?

To simply drive Q3, the step-down method can be used.

czh778439397

How to use voltage reduction? Please give me some advice! I have been struggling for a long time, and I am just missing this step!

philipchiu

Improper design ideas,

czh778439397

philipchiu posted on 2018-6-17 22:19 The design idea is inappropriate,

Can you please give me some advice on how to improve it?

maychang

czh778439397 posted on 2018-6-17 21:17 I just want to achieve Vo=Vin1*D1+Vin2*D2, when the solar energy decreases, the mains output automatically increases, when the solar energy increases, the mains output automatically decreases, ...

I doubt very much "I just want to achieve Vo=Vin1*D1+Vin2*D2, when the solar energy decreases, the mains output automatically increases, when the solar energy increases, the mains output automatically decreases, and the total output voltage Vo remains unchanged." To obtain the same energy, the mains is the cheapest, cheaper than solar energy. From an economic point of view, cheap energy should be used first, and more expensive energy should be used only when cheap energy cannot be obtained. For example, you use the mains electricity to light the basement and charge the backup battery at the same time, and then use the battery when the power goes out. Your plan, on the other hand, is to use expensive energy first, and then switch to cheap energy when expensive energy is not available. I don't know what you are thinking, but you must give up the near and seek the far.