SB240 diode test ?

[bianchi77]

Guys,

I've tested SB240 with diode test on DMM...
and I got 0.115V and 0.127V on both side red and black probe of DMM vice versa....

I reckon it's faulty...because diode normally only doing one way and the other is OL...

Comments ?

[stj]

Re: SB240 diode test ?

a schotky diode can react like that on some meters.

[bianchi77]

Re: SB240 diode test ?

so how can I determine if it's ok ?

[stj]

Re: SB240 diode test ?

use a battery & bulb - see if it only lights one way

[bianchi77]

Re: SB240 diode test ?

ok..that's good idea

[bianchi77]

Re: SB240 diode test ?

if it's a rectifying diode on switching regulator and there's a short on its output...it's most likely faulty isn't it ?

[bianchi77]

Re: SB240 diode test ?

I'm testing it with battery and LED...it's normal...
another one...I have SBL1040....I've tested with LED and battery...forward and reverse bias...it's normal, but when I tested this SBL1040 on diode test DMM it's 0.17V....it's faulty, isn't it ?

I used LED, resistor 1K and 9V battery performing the test..

[stj]

Re: SB240 diode test ?

not sure what you mean,
if a diode is shorted then it's bad.
but if your just metering the output of a psu, many have a low ohms resistor across the output that will fool your meter.

[stj]

Re: SB240 diode test ?

I'm testing it with battery and LED...it's normal...
another one...I have SBL1040....I've tested with LED and battery...forward and reverse bias...it's normal, but when I tested this SBL1040 on diode test DMM it's 0.17V....it's faulty, isn't it ?

I used LED, resistor 1K and 9V battery performing the test..

if the lamp only works one way - it's working.

[bianchi77]

Re: SB240 diode test ?

if the lamp only works one way - it's working.

Doesn't matter if DMM = 0.17V ?

[budm]

Re: SB240 diode test ?

Use 9V, 100 Ohms resistor in series with DUT (to simulate about 90mA of If) to forward bias the diode and use your meter to read the Vf of the diode under test to see what you get.
Vf will very with current flowing through the DIODE, Temperature also affect Vf.
If you test setup show LED lights in one direction only with that diode, the the diode is OK.
You can also use your variable power supply to reverse bias the diode to see if it will break down way before the Voltage break down spec. of the diode.

[bianchi77]

Re: SB240 diode test ?

if I use 90mA...will the LED stand...or it will be very bright...

[stj]

Re: SB240 diode test ?

very very very bright, most led's are only rated for 30ma!

[bianchi77]

Re: SB240 diode test ?

That's what I'm thinking...will it burn only in few seconds ?

[TechGeek]

Re: SB240 diode test ?

probably; that's 4.5x more than it's rated for!

[budm]

Re: SB240 diode test ?

if I use 90mA...will the LED stand...or it will be very bright...

No LED! We are just trying to read Vf of the Diode with about 90mA through it. You can look at the Vf graph of the diode with relation to the current in the spec sheet.
That why I said 9V, 100 Ohms resistor, and the DUT.

[bianchi77]

Re: SB240 diode test ?

ok...9V -->100 Ohm --> Device Under Test (diode)...and my DMM on diode test mode to see the voltage on diode ?

[bianchi77]

Re: SB240 diode test ?

compare with this chart ....

[bianchi77]

Re: SB240 diode test ?

with DMM diode test on 90mA Vf must be inside the red circle, correct me if I'm wrong

[budm]

Re: SB240 diode test ?

https://cdn.badcaps-static.com/pdfs/...de6c30ae15.pdf
https://cdn.badcaps-static.com/pdfs/...2f0cb7ec39.pdf

Not all brand will have same exact Vf.
So just try it and see what you get.