Identify replacement diode

[jezzaaaa]

I'm trying to find a replacement diode for one that has gone short.

I have a generic USB charger that went short circuit to ground on 5V. I found that one of a pair of identical diodes in parallel (and in series with transformer secondary winding) has gone short in both directions, so I suspect it's bad. The marking is CSRS1045, which I believe is a low barrier Schottky with max current 10A and max reverse 45V. I found a spec sheet for CSRS1045-A that has same specs and also says 350mV drop when forward biased.

I can't find the exact part number for sale. Similar ones such as 10SQ045 have the same 10A/45V specs, but forward voltage drop of 550mV. Is that close enough? Does the V(f) make enough difference in my application that I need to worry about this?

Also, when I measure the other diode on my DMM in diode mode, it shows 90mV. Does this mean that diode is bad also, if the ? It shows open when reversed biased.

[CapLeaker]

Re: Identify replacement diode

Just put any other Schottky diode in that has close enough specs. The closest match I could find fast is this one at Mouser.
Mouser Part #
241-SBM1045VSSAY0000
Remember the Schottky has a low forward voltage drop compared to regular diodes.

[stj]

Re: Identify replacement diode

if it had 2 in parallel then thats bad design,
use a single replacement that has double the current handling - maybe in a to220 package for extra cooling.
like an MBR40250G

[petehall347]

Re: Identify replacement diode

if you have to replace as a pair match the vf and check if they both stay same vf at different temperatures .

[CapLeaker]

Re: Identify replacement diode

Or put one larger fast recovery schottky in.

[jezzaaaa]

Re: Identify replacement diode

if it had 2 in parallel then thats bad design,

Thanks for the info. Can you elaborate on why this is bad design? A few times I've seen some circuits double-up on components to double their combined ratings, and I just figured it was much cheaper to use two common components that a single less-common but higher-rating equivalent. I suppose in the case of a pair of diodes, if the forward voltage is slightly lower on one, that might mean all current flows through that diode?

use a single replacement that has double the current handling - maybe in a to220 package for extra cooling.
like an MBR40250G

That's an interesting idea. There's almost certainly room for a 2-lead TO220 package. But at 860mV, the MBR40250G has a much higher forward voltage drop than the 350mV on the spec sheet of the CSRS1045-A. Are you saying the forward voltage drop isn't important enough in this application to worry about?

[jezzaaaa]

Re: Identify replacement diode

Just put any other Schottky diode in that has close enough specs. The closest match I could find fast is this one at Mouser.
Mouser Part #
241-SBM1045VSSAY0000

Yay, the specs on that look very close. Thanks dude! I'll try to source some of those.

[jezzaaaa]

Re: Identify replacement diode

Yay, the specs on that look very close. Thanks dude! I'll try to source some of those.

Nothing on Aliexpress or eBay. Mouser and Digikey cost AUD25+ just for shipping. It'd be cheaper to buy a replacement charger. I don't mind spending $10 to keep eWaste our of landfill, but $25 us a bit much.

[stj]

Re: Identify replacement diode

the voltdrop is at maximum current - check the curve charts in the datasheets

[jezzaaaa]

Re: Identify replacement diode

the voltdrop is at maximum current - check the curve charts in the datasheets

Right, that makes sense.

So the "instantaneous forward current" graphs show Vf vs If at various temps. I figure as the charger has 2.4A and 1A outputs, total 3.4A, and each diode would probably take half the current, that makes about 2A with losses. Inside the charger would probably not exceed 25C.

The CSRS1045-A line lands on about 350mV. The same on the MBR40250 lands on about 660mV. The SBM1045VSS comes in at around 380mV.

[stj]

Re: Identify replacement diode

they will all work,
the higher the loss the warmer they will get - thats all really.