[moved] Can Mosfets work as ideal switching voltage dividers?

[STHOTA]

Hi, I tried this circuit both in simulation and in practical manner. Below i used a gate driver IR2112 to drive the gates of the two mosfets, which boosts my PWM 5V amplitude signal to PWM 15V. My goal is to get equal distribution of voltage of the DC rail input applied to the drain of Q1 at the drain of Q2. It works perfectly well in the simulation. when Vds of Q1 is 20V, Vds of Q2 is 0, Vds of Q1 is 0, Vds of Q2 is 20V, Vds of Q1 is 10V, Vds of Q2 is 10V and it's working similarly with a DC rail of 100V too.(EQUAL DIVISON) But experimentally with the same components, I am getting a constant Voltage drop of 10V across Q2. The Vds of Q2 remained constant and thus the output is a constant of 10V irrespective of DC rail power supply.

Is there any way I could change my circuit to get an equal potential division experimentally? Thank you

 

[crutschow]

It likely works in simulation because the simulated MOSFETs are identical.
In practice they aren't.

If you explain what you are trying to achieve, we may be better able to help you.

What is the purpose of having half the rail voltage at the drain of Q2?
Are you trying to do a rail split?
If so you need an analog circuit, not a digital one.

 

[KlausST]

Hi,

If so you need an analog circuit, not a digital one.

If you expect current beyond 100mA I´d go for a switching solution. 50% duty cycle.
But add an LC low pass filter to get a DC voltage.

Klaus

 

[FvM]

Correct gate driver circuit according to IR2112 datasheet, remove R3 or reduce it's value considerably.

 

[STHOTA]

My main aim is to generate AC from DC supply.
Below is the circuit. I am generating 2 PWM Pulses of 5V amplitude each with 180 phase shift (say SVMA & SVMB in the fig) using Arduino. The gate driver needs to boost these PWM signals to 15V amplitude pulses in order to turn on Gates of Mosfets. The 4 Mosfets work like a H bridge circuit. The DC rail input if for suppose is 240 Vdc, the two output terminals should provide 120 VAC as the final output. The capacitor and inductor inside the H bridge works on smooth sine wave generation. I tried this circuit in simulation and it worked perfectly well. I connected this circuit on breadboard, but it is now not giving any output. Seeking some help. Thank you.

 

[STHOTA]

Yes. I actually require a voltage of 120 VAC with 2 amps of current at the final output. I'm attaching a full circuit now. please have a look at it.
Thank you

 

[STHOTA]

I removed R3 and worked experimentally. It didn't make any difference to the output. I will decrease the resistance value and check too. Thanks

 

[betwixt]

As already recommended, please read the data sheet and correct the design.

Do I understand from post #5 that you are driving this from 240V DC and trying to produce 120V AC out of it?

Brian.

 

[STHOTA]

@betwixt, Yea i'm going to order ir2110 gate driver and replace it. I will connect it according to the data sheet.
Yes you are right. I got that part of getting DC from AC.

 

[KlausST]

Hi,

Safety first: You are working with dangerous voltage! Don't risk electrical shock or fire!

, but it is now not giving any output.

What exactely does this mean?
* show the TTL pwm signsl on a scope
* show the gate driver output signsl on a scope
* show the H bridge output on a scope

Some issues:
* a breadboard is not suitable for switching power applications
* a breadboard is not suitable for 240V operation. Don't risk your health
* IRF3315 is not suitable for 240V operation
* 15V supply needs a bulk capacitor and several fast decoupling capacitors
* what are R8, R9, R12, R13 good for?
* you need to tell us PWM frequency
* don't use duty cycle of 100%
* consider to use 100nF for C4 and C6
* for this SPWM technique...how do you generate the PWM signals?
* what is C1, C2, R1, R2, R3, R4, L1 good for? What do you want to achieve with it?

Klaus