Author Topic: replacing flywheel diode in SMPS  (Read 3185 times)

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Offline SnakeBite

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replacing flywheel diode in SMPS
« on: July 30, 2012, 02:13:18 pm »
Hi,
i'm attempting to repair my speaker amplifier and there is a flywheel diode there on the DC to DC converter. the diode model is MUR1520 and i'vi don't have it available here in Israel (i know ebay have it) so i found a diode form the same manufacturer that has almost identical specs.

except:


DC Blocking Voltage of 600V instaed of 200v in the original - which i think it's OK.
Average Rectified Forward Current of 120A instead of 200A - which i also think it's OK since it's 300w buck converter.
Reverse Recovery Time of 30ns instead of 35ns - quicker is beter i think.
Maximum Instantaneous Forward Voltage: at 25c:  2.2V instead of 0.85v in the original - i don't know if this 1.35V is critical
                                                              at 125c: 1.6V instead of 1.05V in the original - i also don't know.
here are the datasheets:
www.onsemi.com/pub/Collateral/MUR1520-D.PDF
www.irf.com/product-info/datasheets/data/15eth06.PDF

here is the circuit of the DC - DC converter
http://www.tgahinfo.homecall.co.uk/S750%20PSU/Data%20Sheets/Buck.jpg
it's mark as D4.

thanks
Idoaricha
Ido Aricha , Israel.
 

Offline SeanB

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Re: replacing flywheel diode in SMPS
« Reply #1 on: July 30, 2012, 04:05:45 pm »
Not going to make a difference. What killed the original diode, they normally only fry if they fall off the heratsing or the capacitor goes short circuit. The higher voltage drop is only going to increase the standoff voltage on the switching transistor by that amount, Not an issue with 600v there to begin with.
 

Offline SnakeBite

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Re: replacing flywheel diode in SMPS
« Reply #2 on: August 02, 2012, 09:54:45 am »
it's works now!!
thanks :)
Ido Aricha , Israel.
 

Offline amyk

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Re: replacing flywheel diode in SMPS
« Reply #3 on: August 02, 2012, 10:35:55 am »
Keep in mind that the higher forward voltage can cause it to run hotter due to the higher power dissipation, this is more important if you're replacing a main output rectifier.
 

Offline SnakeBite

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Re: replacing flywheel diode in SMPS
« Reply #4 on: August 03, 2012, 01:24:51 pm »
i check the forward voltage before i insert the diode and it read 0.4V so i don't think it's too bad.
the voltage i mention is the MAXIMUM voltages. and the 15ETH06 diode that i put now is rated for 600v max forward voltage vs 200v in the mur1520. so i think it will be fine.

Ido Aricha , Israel.
 

Offline T4P

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Re: replacing flywheel diode in SMPS
« Reply #5 on: August 03, 2012, 03:43:08 pm »
0.4V at the currents your meter is reading at.
If the average current drawn is 2amps it easily goes up to 0.7V @ 150C
or if it's at 25C it's 1.35V
1.35*2 = 2.7W ...
if you leave it without a heatsink on the board this is going to be overheated easily ... if it's a TO-220
1C+70C/W = 71C 71*2.7 = 191.7C ...
just remember to solder the thermal pad using a hot air if you use the DPAK
 


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