1
\$\begingroup\$

i have made simple inverter circuit with z44 MOSFET but circuit work for minutes and the primary coil start heating then shorting finally damage the MOSFETF, it is my 6th time facing this issue. i have no idea how to protect the MOSFET. Why this is happening and is there anything i have to improve ?

any idea would helpful

thanks!!

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
11
  • 2
    \$\begingroup\$ Heatsink your MOSFETs. Also, they are probably switching on and off too slow due to the high resistances at the gate which means a lot of time spent as resistors dissipating power. It would help if you knew the frequency it was running at and the peak current. \$\endgroup\$ – DKNguyen Aug 14 '20 at 14:17
  • 1
    \$\begingroup\$ Do you have a scope? How did you design the transformer? What's its primary inductance? What is the switching frequency? Have you measured the supply current with no load? \$\endgroup\$ – user_1818839 Aug 14 '20 at 14:18
  • 1
    \$\begingroup\$ You might want to connect M2 source to GND. \$\endgroup\$ – user_1818839 Aug 14 '20 at 14:35
  • 2
    \$\begingroup\$ First, you need a scope to check the frequency, drain-source votlages and drain currents. The gate voltages for the MOSFETs are 6VDC (due to 1k-1k divider). Check the Vds-Id graphs from this document (Fig.2). Maybe there's a lot of dissipation for your current-voltage levels. \$\endgroup\$ – Rohat Kılıç Aug 14 '20 at 15:00
  • 1
    \$\begingroup\$ Step 1: Figure out why it's failing. Step 2: Fix that. Is it simply overheating? Are you exceeding the voltage or current limits? Is the transformer core saturating causing the current to be higher than you thought? \$\endgroup\$ – user253751 Aug 14 '20 at 15:35
4
\$\begingroup\$

Why this is happening and is there anything i have to improve ?

Your circuit has no fly-back protection circuit to prevent back emfs from transformer primary leakage inductance. It's crucial that some form of protection be applied if you are to avoid voltage fly-back exceeding the limit on the IRFZ44 MOSFETs (55 volts but no more).

enter image description here

The above is an example of a snubber that dissipates the energy from the leakage inductance.

\$\endgroup\$
4
  • 1
    \$\begingroup\$ @DKNguyen no, not diodes to centre point. The centre-point is the fulcrum of a seesaw. When one end goes down to 0 volts, the other end rises up to twice Vcc and the leakage spike is on top of that. Transformer action! \$\endgroup\$ – Andy aka Aug 14 '20 at 19:38
  • \$\begingroup\$ Oh yeah. You're right. It isn't just a dead half winding during the other cycle. You would need bidirectional TVS clamp diodes, not unidirectional diodes. \$\endgroup\$ – DKNguyen Aug 14 '20 at 23:34
  • \$\begingroup\$ So I have to add rc snubber circuit, but it have effect on the frequency \$\endgroup\$ – Ananiya Jemberu Aug 15 '20 at 5:05
  • \$\begingroup\$ It needs calculating properly. Like, how much resistance can snub the spike to below the peak limit of the MOSFET and like, how little capacitance can be in series without making the snubber ineffective. \$\endgroup\$ – Andy aka Aug 15 '20 at 9:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.