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how hot should a schottky get?

My dvd-dtt unit recently failed to start up. As I suspected, there was a bulged 1000uf 35v cap on the psu secondary so I changed it , and the associated rectifier diode ( a 1N5822) as the pcb looked toasted and I suspected it might have gone a bit leaky.

As replacement I used an SB340 (

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) from the spares box. the unit now works but the diode seems to be running hot - you can keep your finger on it - just - in use. Is this usual? At least it doesn't seem to be getting red hot....

-B

Reply to
b
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what f is it handling ?

Reply to
N_Cook

Absolute maximum current is 3A, at a forward drop of 0.5 V, so max power dissipation is 1.5W. The typical thermal resistance is 20C/W, so the max temperature rise should be 30 C. Can you keep your finger on a

55C temp surface?

Any $10 multimeter should be capable of measuring all three parameters.

Reply to
spamtrap1888

Thanks for the suggestions guys. left it on for a few more hours, and the temp. didn't seem to get out of hand. Above calculations noted, many thanks. I suspect this is just a poor design, the psu is a tiny crappy circuit board, no regulators in sight just crude diodes and caps. Lots of pcb area was scorched as things obviously ran hot/at the limits of their tolerances from the word go.

Will do some more exhaustive soaktesting and if things deteriorate, will check the voltage drop and current as sugested. For now I've just got it off the bench for more pressing things. regards, B.

Reply to
Ben Roberts

Thanks for the suggestions guys. left it on for a few more hours, and the temp. didn't seem to get out of hand. Above calculations noted, many thanks. I suspect this is just a poor design, the psu is a tiny crappy circuit board, no regulators in sight just crude diodes and caps. Lots of pcb area was scorched as things obviously ran hot/at the limits of their tolerances from the word go.

Will do some more exhaustive soaktesting and if things deteriorate, will check the voltage drop and current as sugested. For now I've just got it off the bench for more pressing things. regards, B.

Reply to
b

If you have any sort of a spare heatsink, it wouldn't hurt ot use it, might help and can't hurt.

Reply to
hrhofmann

For every 10 C rise in operating temperature the MTBF for a component goes to one half, lasts on the average half as long. So, cooler IS better.

Most of the heat goes out the legs, some out the body.Remember in convection air te rule of thumb is 1 C rise per watt per 100 square inches

Reply to
Robert Macy

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