replacing schottky diodes on a AV power supply

[DjKrish]

Hi guys, i have a power supply with a shorted SR320 schottky diodes which is in parallel. Only 1 shorted while another is ok. So i removed the faulty one, the power supply is working fine now. SR320 is 3A 20V. I was thinking can i remove both diodes and replace SR340 as 1 diode as it is 3A 40V? Because i dont have SR320. Or can i replace both with SR340?

[stj]

Re: replacing schottky diodes on a AV power supply

neither, your going to need 6A at 20v, not 3A at 40v
parallel diodes double the current, not the voltage

if you check my Ryobi charger thread, i replace a couple of diodes with a 25A to220 package part

[DjKrish]

Re: replacing schottky diodes on a AV power supply

neither, your going to need 6A at 20v, not 3A at 40v
parallel diodes double the current, not the voltage

if you check my Ryobi charger thread, i replace a couple of diodes with a 25A to220 package part

6A 20V, noted, will try that. Cause i fitted the 3A 40V diodes, no power at all. When i fit back the single 3A 20V, its working again.

[stj]

Re: replacing schottky diodes on a AV power supply

higher voltage is fine - infact with schottky's you really want 10x the running voltage.

https://www.badcaps.net/forum/showthread.php?t=54038

[budm]

Re: replacing schottky diodes on a AV power supply

6A 20V, noted, will try that. Cause i fitted the 3A 40V diodes, no power at all. When i fit back the single 3A 20V, its working again.

That does not make any sense.
What exactly did you put in?

[DjKrish]

Re: replacing schottky diodes on a AV power supply

That does not make any sense.
What exactly did you put in?

Its a home theaters SMPS. I know, it doesn't makes any sense either. But i dont know, i took out the old one, put in 2 new SR340, power on, no power. Pull out again, put in the old SR320 diode, its working and i was like LOL

[DjKrish]

Re: replacing schottky diodes on a AV power supply

I tried the following.

1 piece of SR340
2 piece of SR340
1 piece of SR320 and 1 piece of SR340

None works. If i pull all and put only 1 piece of SR320, it works. Sighs

[budm]

Re: replacing schottky diodes on a AV power supply

What happen if you test the SR340 and compared to the SR320 with you meter?

[DjKrish]

Re: replacing schottky diodes on a AV power supply

What happen if you test the SR340 and compared to the SR320 with you meter?

SR320 - 15.33v
SR340 - 5.56v

No wonder theres no power when i put SR340. I wonder why

[stj]

Re: replacing schottky diodes on a AV power supply

i dont understand where you got the numbers,
test the diodes with your diode-test on the meter - both directions.

[DjKrish]

Re: replacing schottky diodes on a AV power supply

i dont understand where you got the numbers,
test the diodes with your diode-test on the meter - both directions.

test on V mode while power on.

while take off from board, these are the reading on diode mode

sr320 - 0.343v
sr340 - 0.164v

[stj]

Re: replacing schottky diodes on a AV power supply

the sr320 looks fucked for a schottky - thats far too much voltdrop
probably damaged - just not as much as the other one.

[petehall347]

Re: replacing schottky diodes on a AV power supply

both should be vf 0.55
https://cdn.badcaps-static.com/pdfs/...5f72338fd7.pdf

[stj]

Re: replacing schottky diodes on a AV power supply

that's at max current, they generally meter at about 0.18 on a meter

[momaka]

Re: replacing schottky diodes on a AV power supply

parallel diodes double the current, not the voltage

Theoretically that's correct.

However, if the diodes are not built on the same physical die (as is the case here, where O/P has two separate diodes wired in parallel on the PCB), then one diode will run hotter than the other. When that happens, the forward voltage of the hotter diode will drop further, making the the circuit "prefer" to push more current through that diode, which will in turn heat up the diode even more. If this continues, thermal runaway may eventually kill the diode if the circuit has the capacity to push a sufficiently large current through it.

Because of that, I agree with what STJ suggested: use a single 6 Amp (or higher) diode/rectifier (and preferably Schottky type for lower losses.)

both should be vf 0.55
https://cdn.badcaps-static.com/pdfs/...5f72338fd7.pdf

That's the maximum expected voltage drop at the rated current of the diode (3 Amps). Most multimeters push much much less than that when testing components (typically in the order of a few uA to maybe a fraction of a mA max.) As such, the Vf will appear much lower. Figure 3 in the above datasheet shows Vf for any given current from 0.1 Amps to rated surge current. You can see that for 0.1 Amps of current, the Vf is around 0.2V for SR320-340. So with a multimeter, the Vf should likely show even lower value... though depending on multimeter quality/design, that may not always be the case.

[DjKrish]

Re: replacing schottky diodes on a AV power supply

This is the section. Output is 12V.

[budm]

Re: replacing schottky diodes on a AV power supply

So when you install SR340 you say you no longer get the switched B12V?
When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
Is switched B31V present when that happen?
Can you also provide the full PDF of the service manual?

[DjKrish]

Re: replacing schottky diodes on a AV power supply

So when you install SR340 you say you no longer get the switched B12V?
When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
Is switched B31V present when that happen?
Can you also provide the full PDF of the service manual?

Heres the pdf file.

[DjKrish]

Re: replacing schottky diodes on a AV power supply

Sorry, heres the PDF file

[DjKrish]

Re: replacing schottky diodes on a AV power supply

So when you install SR340 you say you no longer get the switched B12V?
When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
Is switched B31V present when that happen?
Can you also provide the full PDF of the service manual?

SR340 - 5v plus
SR320 - 12v plus
B31V present