SNUBBER resistance burns out in seconds(SMPS)

sagarverma · 24th June 2006, 04:26 PM

Hello all,
http://sound.westhost.com/project89.htm >> the schematic of the SMPS in question.
i have used snubber in it(68r/2w+100nf).
without these the output voltage is much more than what the turns ratio permits,using these the output voltage is perfect but the resistance heats up and ultimately burns out in seconds.i then used 5W res also but to no avail.

Sagar

poobah · 24th June 2006, 04:33 PM

What type and voltage is your snubber cap?

What is your primary bus voltage?

sagarverma · 24th June 2006, 04:36 PM

i think u havent read the post carefully......

Sagar

poobah · 24th June 2006, 04:36 PM

see the edit -

sagarverma · 24th June 2006, 04:43 PM

your edit was seconds late.
The cap was bead capacitor and rated at ??volts.
i replaced it with polyester(philips) at 105volts.
But in either case the res burns out.
Primary voltage is given in the schematic of the SMPS.(12v square wave)

Sagar

poobah · 24th June 2006, 04:50 PM

Are the caps shorted?

sagarverma · 24th June 2006, 04:51 PM

no... Why should they be?

Sagar

jackinnj · 24th June 2006, 04:59 PM

Quote:

Originally posted by sagarverma
Hello all,
http://sound.westhost.com/project89.htm >> the schematic of the SMPS in question.
i have used snubber in it(68r/2w+100nf).
without these the output voltage is much more than what the turns ratio permits,using these the output voltage is perfect but the resistance heats up and ultimately burns out in seconds.i then used 5W res also but to no avail.

Sagar

if you don't know the ringing frequency and the peak to peak charge held by the capacitor there isn't much point to the discussion -- you can't just pull capacitor and resistor values out of a hat (which many are wont to do) --

the snubber resistor must be able to dissipate P >= C f V^2

usually a value in the low nF's is specified, you are using a value 100x greater so the dissipation factor is 100x greater.

knowing the inductance of the trafo primary and secondaries, the junction capacitance of the switching devices will give you a first approximation of the snubber values --

sagarverma · 24th June 2006, 05:04 PM

Dear Jackinjj
i havent taken arbitary res value.
these are mentioned in the circuit.i have made excatly that circuit.Even the switcher res and caps are the same.
regarding 68R instead of 56R,i tried 56R also but to no avail.

Sagar

poobah · 24th June 2006, 05:16 PM

What is the switching frequency?

24th June 2006, 04:26 PM	#1
sagarverma diyAudio Member Join Date: Feb 2005 Location: NEW DELHI	SNUBBER resistance burns out in seconds(SMPS) Hello all, http://sound.westhost.com/project89.htm >> the schematic of the SMPS in question. i have used snubber in it(68r/2w+100nf). without these the output voltage is much more than what the turns ratio permits,using these the output voltage is perfect but the resistance heats up and ultimately burns out in seconds.i then used 5W res also but to no avail. Sagar __________________ Never Underestimate The Bandwidth of A Station Wagon Full Of Magnetic Tapes Hurtling Down The Highway...................Andrew S Tanenbaum

24th June 2006, 04:36 PM	#3
sagarverma diyAudio Member Join Date: Feb 2005 Location: NEW DELHI	i think u havent read the post carefully...... Sagar __________________ Never Underestimate The Bandwidth of A Station Wagon Full Of Magnetic Tapes Hurtling Down The Highway...................Andrew S Tanenbaum

24th June 2006, 04:43 PM	#5
sagarverma diyAudio Member Join Date: Feb 2005 Location: NEW DELHI	your edit was seconds late. The cap was bead capacitor and rated at ??volts. i replaced it with polyester(philips) at 105volts. But in either case the res burns out. Primary voltage is given in the schematic of the SMPS.(12v square wave) Sagar __________________ Never Underestimate The Bandwidth of A Station Wagon Full Of Magnetic Tapes Hurtling Down The Highway...................Andrew S Tanenbaum

24th June 2006, 04:51 PM	#7
sagarverma diyAudio Member Join Date: Feb 2005 Location: NEW DELHI	no... Why should they be? Sagar __________________ Never Underestimate The Bandwidth of A Station Wagon Full Of Magnetic Tapes Hurtling Down The Highway...................Andrew S Tanenbaum

24th June 2006, 05:04 PM	#9
sagarverma diyAudio Member Join Date: Feb 2005 Location: NEW DELHI	Dear Jackinjj i havent taken arbitary res value. these are mentioned in the circuit.i have made excatly that circuit.Even the switcher res and caps are the same. regarding 68R instead of 56R,i tried 56R also but to no avail. Sagar __________________ Never Underestimate The Bandwidth of A Station Wagon Full Of Magnetic Tapes Hurtling Down The Highway...................Andrew S Tanenbaum


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24th June 2006, 04:33 PM	#2
poobah diyAudio Member Join Date: Nov 2005	What type and voltage is your snubber cap? What is your primary bus voltage?

24th June 2006, 04:50 PM	#6
poobah diyAudio Member Join Date: Nov 2005	Are the caps shorted?

24th June 2006, 05:16 PM	#10
poobah diyAudio Member Join Date: Nov 2005	What is the switching frequency?

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