Thread: M542 Driver
Nice one let us know how you get on...
Right then have new components arrive today, the circuit will not power up without it and problem now is which way round should it go?
if i was to just bridge it it would be closed circuit. I'm now thinking the diode is part of clamping circuit maybe? if this was the case then the negative side of the diode would need to go to the negative side of circuit?
It does not make sense to just have a diode across the power lines as a protection circuit right? am i missing something here? wish i had a circuit diagram. The board won't clean up enough for me to see the tracks eitherIf the nagging gets really bad......Get a bigger shed:naughty:
Yes tracks are fine, it is only the mask discolored but i would not want to scrape that awayIf the nagging gets really bad......Get a bigger shed:naughty:
A protection diode usually has it's cathode connected to the positice supply and it's anode connected above where you will break the circuit.
When the circuit breaks the supply to a coil the coil impedance wants to keep the current flowing. If it has nowhere to go the Volts go through the roof, probably exceeding the breakdown point of the transistors.
The diode carries the excess current back to the top of the coil so it can go round and round until the coil resistance eats it up.
Expect the cathode, stripe, to be at the positive supply end of the circuit.
Robin your correct, last night i thought what the hell, spend hours pondering and testing or just solder it in. The worse that could happen is it goes pop, well it did so i put another one in the other way round it works a treat :-)
The part number is SMAJ48A-TR from RS for all those lurkers waiting for itIf the nagging gets really bad......Get a bigger shed:naughty:
Glad you fixed it - one day I'll get round to fixing the two broken M752's I have. Not had chance to look at them but I suspect some of the MOSFETs would need replacing.
Bit off topic but...
They're cutting it fine with the MOSFET ratings - both of our M542s use MOSFETs only rated for 55V absolute maximum. Considering they're driving an inductive load and the manual states they can be used on up to 50V I'm surprised the voltage spikes on switching do not exceed 55V. The M752 (75V) and 2m880N (70V) have a much more realistic safety margin as they both use IRF540 MOSFETs which are rated for 100V. I therefore run my M752 drivers on the rated 75V having also checked with oscilloscope that the voltage spikes do not exceed 100V.
Thanks for the info Jonathan. Scarping the mask back was only to make it easier to see the tracks underneath. The tracks are all fine.If the nagging gets really bad......Get a bigger shed:naughty:
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