Technical, Techniques, Hints, and Tips > The "Black Arts!" ( Electrics & Electronics )
Mosfets High Current.
The Old Fart:
I tried putting 2 IRF4905 P channel mosfets in parallel.
10k resistor source to gate.
npn opto isolator. gate to 0v.
Trying to switch on/off a 70A load. no pwm, just straight on/off.
Heatsink gets luke warm, then mosfets overload and fail.
Has anyone else managed to switch a high current using mosfets?
Need to switch positive side.
Brian60:
I've never tried high current switching however are you using lipo's? I could be way off base here but, when switched they may be giving a sudden burst which is overloading the mosfets. Also do you have them attached to a heatsink of suitable size? and using thermal conductive adhesive to make the connection?
Failing that, can you change your circuitry to have your switching after the load and allow the N channel mosfets?
I feel your pain, P channel mosfets are expensive compared to their N channel counterparts!
The Old Fart:
Hi Brian60,
Yes to lipo, but switched on at zero load, not until high current applied do they pop.
yes to paste, yes to heatsink,
No to using 'N. type, common 0 v rail through boat.
Mosfets are fully 'switched on' so theory is a very low resistance across the junction, < 0.01 ohm.
Plastic - RIP:
Are you sure the transistor is fully switched on? Under high currents, the supply voltage will collapse and you may end up in a balance where input voltage may cause it to oscillate at high frequency in its linear range so total power dissipation may be momentarily many times more than the device can dissipate - it may blow up so fast the heat never even gets to the outside of the case.You might want to beef up the wiring or replace the girlie TO220 packages with a proper switching block MOSFet.
Brian60:
--- Quote from: The Old Fart on June 25, 2018, 02:20:19 pm ---
No to using 'N. type, common 0 v rail through boat.
--- End quote ---
Same problem I had, however as mine was for many led circuits I was advised to drop the P channel mosfets and use an integrated circuit package which would do the low level switching I required. Absolutely of no help in your situation though.
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