hi guys.
ive been touching alot of smps in the amps ive been fixing lately and i have a few general questions about troubleshooting them.
1- is there anything i can do to separate the smps of the amplifier section itself?
ive seen smps blow up like crazy in the past.im wondering if there is anything i can do to limit the damage in the case of failure?
2- is it doable to remove the power supplies last output fets (or transistors)
when troubleshooting on the primary side and still apply power to the unit without damaging? that way i could probe the switching signal that goes to the fets without risking anything blowing up.
3-what are the usual parts that will blow on a typical smps failure?
other than : output fets, gate resistors, fet driver transistors, switching controller?
(i know it can depend on design but generally)
4- even if i have done alot of electronic repairs i must still ask this question.
is there any heavy precautions you would give me? other than the Vbulk being at ~160vdc.
i thank you very much for your time
ive been touching alot of smps in the amps ive been fixing lately and i have a few general questions about troubleshooting them.
1- is there anything i can do to separate the smps of the amplifier section itself?
ive seen smps blow up like crazy in the past.im wondering if there is anything i can do to limit the damage in the case of failure?
2- is it doable to remove the power supplies last output fets (or transistors)
when troubleshooting on the primary side and still apply power to the unit without damaging? that way i could probe the switching signal that goes to the fets without risking anything blowing up.
3-what are the usual parts that will blow on a typical smps failure?
other than : output fets, gate resistors, fet driver transistors, switching controller?
(i know it can depend on design but generally)
4- even if i have done alot of electronic repairs i must still ask this question.
is there any heavy precautions you would give me? other than the Vbulk being at ~160vdc.
i thank you very much for your time
items used to test offline SMPS
1> isolation XFMR
2> Variac
3> analog AC current meter on output of Variac
4> various DC loads inc. electronic loads
the PWM controller usually has some housekeeping supply that you can run off a lab supply. lets you check a lot of the driver signals. then monitor the current(s) while slowly raising the variac. There are other 'tricks' but this will get you 90%
1> isolation XFMR
2> Variac
3> analog AC current meter on output of Variac
4> various DC loads inc. electronic loads
the PWM controller usually has some housekeeping supply that you can run off a lab supply. lets you check a lot of the driver signals. then monitor the current(s) while slowly raising the variac. There are other 'tricks' but this will get you 90%
voltage readout is not as useful as a fast AC current display forget digital
I go by variac vibration feel and seeing the meter movement out of the corner of my eye.
probably useful to use a smaller variac with a good low value AC resettable breaker.
before youre looking at the SMPS you have cleared the amplifier from any faults, right?
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i can get that. i use this guy for linear power supplies in series with a bulb. very practical
An externally hosted image should be here but it was not working when we last tested it.
also i read some people also use a light bulb limiter with a smps.
is this good practice? as ive experienced the smps booting and shutting down a couple times before powering up (probably the caps charging then the smps wants to boot but then the light bulb limits current/voltage and it shutsdown for undervoltage protect)
is this good practice? as ive experienced the smps booting and shutting down a couple times before powering up (probably the caps charging then the smps wants to boot but then the light bulb limits current/voltage and it shutsdown for undervoltage protect)
I have done a bit of SMPS design.
I put a resistor in the lower mosfet source to measure current on a scope.
I would then ramp up variac slowly and stop if current was too much.
The failures I have seen are usually mosfet's blowing and going short.
Sometimes the mosfet's blowing can take the SMPS gate driver and SMPS device out too.
If mosfets have gone I remove them and turn on SMPS and look for SMPS device oscillating OK.
If the SMPS has gate driver I check that too as far as possible.
A isolation transformer is good too for safety reasons.
I put a resistor in the lower mosfet source to measure current on a scope.
I would then ramp up variac slowly and stop if current was too much.
The failures I have seen are usually mosfet's blowing and going short.
Sometimes the mosfet's blowing can take the SMPS gate driver and SMPS device out too.
If mosfets have gone I remove them and turn on SMPS and look for SMPS device oscillating OK.
If the SMPS has gate driver I check that too as far as possible.
A isolation transformer is good too for safety reasons.
some reasonS why it goes 1st on a very short list of basic gear.
it lets you O-scope floating mains things on a grounded bench!
most decent SMPS have primary current limit in the design, find the sensor ( usually a current transformer) and monitor it with a scope.
work out the conversion of current to voltage before hand 100:1 into xxx ohms .
always keep an eye towards the variac current when bringing up a sick unit.
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right now i use a scope meter, battery powered that i got because of issues like this [emoji1] because its battery powered i can use anything as ground ref. even virtual ground
true analog guys use analog test gear nothing like instantaneous full bandwith w/o FFT limits
working a failing SMPS you need to be faster, digital stuff is good capture fast events with a good trigger and knowing when things are gonna happen.
working a failing SMPS you need to be faster, digital stuff is good capture fast events with a good trigger and knowing when things are gonna happen.
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don't forget safety , considering you (grounded) are touching the instrument ( live) so it must have ratings for what you are connecting it to ( isolation transformers are tested for this 1500 VAC leakage etc.) I prefer a grounded bench and O-scope. Let the DUT float, once you connect the scope lead the DUT is grounded to that point.
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I would not use a light bulb tester for an SMPS.
The smps draws more mains current as the mains voltage falls.
The bulb will initially drop a lot of voltage even when the filament is cold. that will force the SMPS into high current mode. The bulb will turn on !
i do not have an isolation transformer just yet. ive been thinking of making one myself, i have a stock of identical transformers i could use to make one.
they are 120v-> 24vac 250va
i was planning on putting 2 with the 24vac side back to back.
the only thing i was sure of is if i should connect the isolated output ground to mains earth or not
they are 120v-> 24vac 250va
i was planning on putting 2 with the 24vac side back to back.
the only thing i was sure of is if i should connect the isolated output ground to mains earth or not
No, it wouldn't be floating then would it.
48VAC at 250VA ?
two primaries in parallel and the secondary's in series, still wont give 120V
you would have to careful when you do full load testing. 250VA is pretty small and droops badly esp. EI cores.
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