Im using a 30N06L to switch a 56v DC voltage to drive a transformer. While its connected to my variable power supply everything works fine up to 40v, once I increase the voltage to 48-55v the mosfets start to exponentially increase in current consumption (1 amp) and heat up rapidly. The specs for the mosfet rate it up to 60v. I bought some IRF540 mosfets which are rated to 100V but am worried if there is some saturation issues with the gate voltage off the arduino being too low or something else. They will be arriving on friday but am worried if im missing another problem as ive spent alot of time and money into this and need it solved soon.
For some background this is a active shared transformer battery balancer. I would like to draw 20 amps, the voltage on the batteries can vary between 46-56v. Please dont ask why I need this much balancing or other unnecessary questions.
Without a schematic of how you are driving the transformer it's hard to be very specific but if the MOSFETs are rated at 60V and you are driving an inductive transformer load you may be experiencing breakdown of the device as the transient voltage on the drain could easily spike up well above 60v.
But please, if you have hardware questions such as this, include a schematic!
I thought MOSFETS let current through. And that the voltage (drain to source) increases in this linear region. It will then dissipate power (which it should not do when used as a digital switch...).
It will dissipate power if not switched off, even when showing the 30 mOhm resistance.
Have a look at the datasheet and seen what resistance/performance the device should have.
I think the 5V on the gate is too low to saturate the MOSFET
(look for a logic level MOSFET, or use an additional driving circuit),
also I would pick a device with a higher voltage rating.
Sorry for not uploading a schematic, please see attached. I dont have any specs on the transformer as its something I winded up on my own with a large ferrite core I had. Im running it at 100khz and as I said its working fine at voltages up to when I get higher than 40. Technically its running fine at higher voltages but the mosfets are drawing alot of current and heating up themselves. Only drawing 1 amp of current over those two mosfets.
Would the IRF540 do a better job? Its rated to 100v, or would it still need a higher gate voltage to fully saturate. Or could I step up the arduino voltage to run the mosfet? Im running this at 100khz
I'm not a MOSFET expert... I know the schematic symbol for a MOSFET shows an internal diode but you might need flyback diodes.
Driving inductors can be tricky and every motor driver circuit I've seen has a flyback diode.
It's the current along with the MOSFET's internal on-resistance that normally generates heat so you may simply need a heatsink. I assume the maximum current rating depends on holding the case temperature to room-temperature, as well as fully-saturating it.
I do have a heatsink on them. Technically speaking it does work. Simply that when I increase voltage past 40v it starts to draw power and heat up quickly. If I add a fan I think I can cool the mosfets fast enough. Regardless I would like to obviously not waste power in such a manner and understand why it behaves like this.
Batteries increase and decrease in voltage as they are charged/depleted so yes the voltage varies between 46-56v. Im currently testing it on my variable power supply which can go up to 60v.
That's not the answer to the question I asked. I know the supply voltage varies between 46V and 56V, that is clear from your schematic. At any one moment one of the MOSFETs is off (I hope), my question is 'what do you think the voltage is on the drain of the MOSFET that is off (non-conducting)?'
