Hi everyone,

I will need help. Can somebody help me. I made a circiut like on picture. It's working well when I connect the burden 3A. When I connect burden to 6 A the mosfet getting hot. I need your help.

Thank you

 

Show the schematic with the "burden" connected.

Change the U8 and U9 resistor values from 1kΩ to 10kΩ.

 

I already did it but nothin change. Here is my full schematic.

Link image: http://file.slo-podnapisi.net/slikomat/datoteka/wou05yt5yyoqetwgzw2y.jpg

 

Check the voltage between source and drain of the mosfet when 6 amps is flowing through it I would expect it to be about 0.025 volts. If it is then it is working correctly and the mosfet will be dissipating about 0.9 watts. If it does not have any heat sinking it will get hot. I have also just noticed that if you are controlling the gate by either having the left hand end of R1 connected to Vcc or floating then the gate will be -Vcc with respect to the source (When floating) (-12 to -18 volts) and when it is connected to Vcc the gate will be - Vcc/2 with respect to the source when it is connected to Vcc. (-6 to -9 volts) I don't see how the mosfet can turn off.

Les.

 

R2 should be 10kΩ and connected to the transistor source.

How are you turning the transistor on and off?

 

I turn off with gnd ( resistor R2)

 

I turn off with gnd ( resistor R2)

That will turn on the P-MOSFET in your schematic.
To turn it off the gate-source voltage should be near 0V.

 

Correction to post #4 I would expect the source to drain voltage to be about 0.15 volts, (The 0.025 figure I quated in post #4 is the on resistance in ohms.)
sorry for the error.

Les.

 

That will turn on the P-MOSFET in your schematic.
To turn it off the gate-source voltage should be near 0V.

Yes sorry my mistake. I turn off with VCC. On by GND

 

Yes sorry my mistake. I turn off with VCC. On by GND

Then R2 should be connected to the transistor source.