Drive signal issues with half bridge

MicrosiM

Administrator
Staff member
Hi Microsim i do understand your point but given the price i paid to get a scope for my location, i prefer to let it run first to see if it survives long enough and then connect my scope to it. Since i know the issue is at 210Vac i will replace the mosfet and test it at 109Vac to check for any issues. Do you mean you want a picture of how the components are laid on the board? If yes i can take a picture and post it here


I think you will NEED isolation transformer to your oscilloscope, now or later

Or you cant connect it to your SMPS.

If you dont see whats going on, you are going to lose dozen of Mosfets on the fly.

Please show pictures of your setup, Can you tel me winding ratio you have used for transformer?

Thanks
 
Hi Microsim, my point is not that i dont want to use my scope. Definitely i need it to check the waves but i prefer to first place at least ensure the circuit is stable for a minimum number of time before i connect anything to it and even for my own safety due to avoid heat burns or electric shock. If some running shows that nothing blows up them i can conclude it safe to connect probes to it and monitor whats going on if not i go back a step down in my voltage test level and monitor it again. I will send you the pictures later today, for the winding turns its 50 turns primary and 2X11 turns secondary.
 
Dead mosfet have been replaced and i've checked leakage inductance its 3.4uH I will post 40Vac measurements Vgs Vds transfo pri and sec soon
 
Setup and next steps

Hi Microsim since i've disconnected everything here is the setup diagramSetup.jpg and this is the SMPS circuit closest pic i could shootSMPS PIC.jpg.

Am thinking of rebuilding the circuit on the same board but this time put the oscillator on a card and bring the ETD34 closer to the mosfets. I will check some layouts and post back.

Am also going into the design the current sense circuit: isense ckt.jpg i will implement a simple scheme that connects to the shutdown pin of the ic in case current goes above a calculated threshold it sets the duty cycle to zero. When pin 4 of the TL494 is connected to the 5V ref output the duty cycle becomes zero.I am wondering if a comparator would be better then a transistor scheme. The TL494 also has a built in comparator for average current control which is another option. What do you think?
 
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Hi Microsim thanks for the reply sorry i did not get time to work on it this week i will post back soon with new circuit picture and waveforms
 
New

Hi this is my new schematic:Schematics.jpg component layout:Circuit Layout.jpg and waveforms with 12Vac and 47 ohm resistors loaded on each output:12Vac measurements.jpg

I will change the 1N4148 diodes for the current sense to FR diodes and finalize the current protection before testing with 40Vac
 
New MEasurements

Hi Microsim please find the new measurements. I have tried deadtime but to no success then i have uncoiled and recoiled the ETD core and these are the new measurements:New measur.jpg
at 12Vac
 

MicrosiM

Administrator
Staff member
its very difficult to know what you are doing.

Why you re coiled the ETD?

you have to test at 110VAC minimum, the circuit is working now?

Stable?

Whats going on?
 
Hi Microsim, this was just a check i thought something had gone wrong there but nothing changed turns ratio are same. Ok i will test at 110Vac and show the waves
 
220Vac isolated test

Survived 220Vac isolated test with 200W bulb in series with smps. output loaded with 2X100W bulbs giving +-32V on output no mosfet heating no core heating.
 

MicrosiM

Administrator
Staff member
Survived straight mains 230Vac test with 200W bulb in series with smps and output +-32Vdc with 100W bulbs on each output

Good!

Now, show waves of SMPS, and tell me heat of mosfets, Increase your load to 300W. replace the 200W series bulb with 500W bulb
 
Hi Microsim, i don't think it will handle 300W i designed it for 200W max, 140W normal operation. Mosfet and core are cool nothing heating up. I can show waves with my battery powered oscope(low sample rate but can handle this voltage level). Am waiting for a x100 scope probe to arrive before i can connect it to the big scope. I will connect the SMPS back to my isolation transformer and show the waves.
 
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