problem with MOSFET driving from microcontroller

[Mithun_K_Das]

I'm having trouble to drive MOSFETs from the microcontroller. to get the proper voltage I need to maintain the gate voltage within 8~10V(@Freq.50Hz && Current=4~6mA) DC. But MCU generating 4.96V. I tried all these circuits before. But can't get more than 5.8V in some ckts and in some case I get 10V but constant (Freq.=0).

I can't find what is my fault. please help...

 

[Tahmid]

Are you driving from 12V? In that case, getting 5.8V is fine if your duty cycle is 50%. This means that the gate voltage is in fact 5.8*2 = 11.6V

The last one is faulty. There should be a pull-down resistor from OUT to ground. Besides that the rest seem fine (besides the fact that aside from the 2nd one, all of them invert the input signal).

Hope this helps.
Tahmid.

 

[Mithun_K_Das]

I also think so. but I can't get the proper voltage from the output of a H-Bridge. HVDC=310VDC. and I'm getting only 109V AC from the output with this gate voltage. I tried with CD4013 before, I got 232V in this circuit. Now I'm trying to replace the total control by the MCU. generated the gate signals, but problem is low output voltage. what is the problem then?

 

[Tahmid]

With none of the above circuits can you drive the high-side MOSFET of the H-bridge.

How are you driving the high-side MOSFET which requires isolated ground or bootstrapped supply?

Hope this helps.
Tahmid.

 

[Mithun_K_Das]

That portion is fully ok. I'. taking help from transistor resistor capacitor diode for bootstrap. None of the mosfets become hot/burnt in this way.

 

[Tahmid]

So, try increasing the current to the MOSFET. 4 to 6 mA seems too low. Try to make the MOSFET turn on/off faster if possible.
Another possibility is low duty cycle from the microcontroller. Are you generating the proper signal? Did you check in simulator or oscilloscope? May be you have a low duty cycle, that's why you get low voltage.

Hope this helps.
Tahmid.

 

[Mithun_K_Das]

I don't have oscilloscope so I didn't see the wave. But simulated in proteus. I did this before but can't find the recent problem of low output voltage.

 

[Tahmid]

Check the output voltage at the microcontroller pins. It should be between 2.0V and 2.5V (assuming you are using 5V power supply for the microcontroller). This would indicate duty cycle of around 50%.

When working in power electronics, you should have oscilloscope. While you can make working circuits without oscilloscope, it's better you don't. If you use oscilloscope you know about the waveforms and can make a better product when you're better informed about the waveforms.

Hope this helps.
Tahmid.

 

[Mithun_K_Das]

I know. But I had lost my oscilloscope for some reason. Hope I can manage another one soon. Till then I've to work with all I have now.

 

[Mithun_K_Das]

I found the the problem, Tahmid. DC/DC converter is not producing strong voltage. whenever load is being connected, voltage goes low. not sufficient gate voltage in the mosfets of DC/DC converter side. Hope I repair this soon.