Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default 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 ( http://pdf1.alldatasheet.com/datashe...WTE/SB340.html
) 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
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Default how hot should a schottky get?

b wrote in message
...
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

http://pdf1.alldatasheet.com/datashe...WTE/SB340.html
) 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



what f is it handling ?


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Default how hot should a schottky get?

On Nov 3, 6:54*am, b wrote:
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 (http://pdf1.alldatasheet.com/datashe...WTE/SB340.html
) 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


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.
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Default how hot should a schottky get?

On Nov 3, 8:15*pm, spamtrap1888 wrote:
On Nov 3, 6:54*am, b wrote:

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 (http://pdf1.alldatasheet.com/datashe...WTE/SB340.html
) 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


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.


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.
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Default how hot should a schottky get?

On Nov 3, 8:15*pm, spamtrap1888 wrote:


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?


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.


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Default how hot should a schottky get?

On Nov 3, 7:40*pm, b wrote:
On Nov 3, 8:15*pm, spamtrap1888 wrote:



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?


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.


If you have any sort of a spare heatsink, it wouldn't hurt ot use it,
might help and can't hurt.
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Default how hot should a schottky get?

On Nov 3, 5:40*pm, b wrote:
On Nov 3, 8:15*pm, spamtrap1888 wrote:



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?


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.


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
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