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Mosfet heating

audrialaa

Hello Guys,

 

Currently I am building circuit for high voltage discharge.

I am controlling signal using two dual channel mofsets and supplying them to the transformer ( 100 voltage multiplication).

 

PROBLEM 1: mosfets become very hot and I am afraid that after some time they will get damaged.

PROBLEM 2: If I put diode STTH11A the volatge output becomes very low., less than 100V.

Part of the circuit (circuit for 555 timer is pretty simple, works in abstable state  - not showed):

 

The SN74 is an single inverter, IRF93 Dual channel mosfets.

image

 

Any advices where the problems could be ?

PS: Yes I know cap in the end doesn't do anything image

 

Thanks for help in advance image

 

BS,

A

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  • e14 Contributor
    e14 Contributor

    P channel and N channel MOSFETS are basically opposites. You are trying to drive it both on and off at the same time by trying to use them in parallel. In addition, power MOSFETS have an intrinsic body diode, which is also hurting you. (When one MOSFET is on, the other is conducting through the body diode.) By using them in parallel, they would also attempt to be on, whether the input was high or low. (Well, either the P or N would always be on, depending on the input voltage - high or low.)

     

    You need to use the part with only one side of it or the other, not both tied together. (Alternatively, you could use both sides, but you still can't tie them together like that.) D1 and D2 should not touch like you have them. Potentially, based on the circuit, you could have G1 and G2 tied together, but you really need to understand how these work and be sure that it's how you want to be controlling it.

     

    If any of that isn't clear, let me know and I can try to explain further. I don't see enough of the circuit to be able to say anything about the diode on the transformer and why it's doing what it is. The different traces going to a pad number aren't clear what they would be doing.

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  • e14 Contributor
    e14 Contributor

    P channel and N channel MOSFETS are basically opposites. You are trying to drive it both on and off at the same time by trying to use them in parallel. In addition, power MOSFETS have an intrinsic body diode, which is also hurting you. (When one MOSFET is on, the other is conducting through the body diode.) By using them in parallel, they would also attempt to be on, whether the input was high or low. (Well, either the P or N would always be on, depending on the input voltage - high or low.)

     

    You need to use the part with only one side of it or the other, not both tied together. (Alternatively, you could use both sides, but you still can't tie them together like that.) D1 and D2 should not touch like you have them. Potentially, based on the circuit, you could have G1 and G2 tied together, but you really need to understand how these work and be sure that it's how you want to be controlling it.

     

    If any of that isn't clear, let me know and I can try to explain further. I don't see enough of the circuit to be able to say anything about the diode on the transformer and why it's doing what it is. The different traces going to a pad number aren't clear what they would be doing.

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  • in reply to e14 Contributor

    Thanks for an answer and explanation of dual mosfet. This is the firt project I am trying to use them and this scheme is barrowed from other device. Now I understand why this device stops to work after some time and you need to take it to warranty. Is funny, as that device is  CE certified and even getting new one it breaks - at most it keeps for two month. Seems that somebody wants to earn some extra money..

     

    So, in general to drive the transfomer I should use just P channel on both mosfets and I need to delay one of the signal so that the transformer could work (induce). I am correct ? As the single inverter inverts the signal from the timer and supplies it to second mosfet (timer gives pulse signal from 0V to +1.5V).

    image