1N5819 diode acting strange???

Thread Starter

BillMail

Joined May 26, 2011
4
I have a GPS wall charger that isn't charging the GPS even though the charger's power light is on and the GPS light is on when connected. I opened the charger up and tested each circuit component with my multi meter and found that when I put my meter on the diode setting, that one of the diodes (1N5819) seemed to have a reading no matter which side I put the positive and negative leads to.
Not finding much info on the web on this particular diode, is this normal for this diode?
I thought all diodes will only have a reading in one direction not both.
Where can I find this diode...Digikey didn't seem to have it.
 

ErnieM

Joined Apr 24, 2011
8,377
It depends if there is anything else in the circuit in parallel with that diode.

Can you test the chargers output directly? Any volts there? (I have the feeling you can't access that point).
 

SgtWookie

Joined Jul 17, 2007
22,230
What do you mean by "it has a reading"?
Are you using a diode test function on your meter?

1N5819's are 40v 1A Schottky diodes; they have a low Vf and are fast switching. Diodes do sometimes fail shorted. They can also fail open.
 

Thread Starter

BillMail

Joined May 26, 2011
4
ErnieM:
I am testing at the leads of the diode so there shouldn't be anything else screwing with the results.
SgtWookie:
As I stated in my original post ....when I put my meter on the diode setting, that....
Most diodes that I am aware of will only give a reading in one direction...for example negative meter lead touching the diode lead at the silver band side and positive lead touching the opposite side yields a meter reading of some value. Reverse those meter leads and there is no reading on the meter.

This diode gives a value (reading) no matter which way I connect the meter leads to the diode, thus my question.
 

Thread Starter

BillMail

Joined May 26, 2011
4
Thanks for that bit of info. I will disconnect one of the diode leads from the circuit board and try again. I assume doing that should yield a reading in one direction only for this diode correct?
 

tom66

Joined May 9, 2009
2,595
Thanks for that bit of info. I will disconnect one of the diode leads from the circuit board and try again. I assume doing that should yield a reading in one direction only for this diode correct?
How is the diode connected to the board? It is possible it is an input protection diode, to prevent damage from reversed polarity. But it could also be used in a switchmode PSU. In which case you could be measuring the inductor, or the internal power switch of some IC.
 

Thread Starter

BillMail

Joined May 26, 2011
4
Isolated the diode and it is functioning properly. That was my last hope for trying to figure out why my GPS charger shows power on the charger and GPS and yet doesn't charge the GPS battery.
Oh well, off to get a new charger.
Thanks to all for the help
 

Ron H

Joined Apr 14, 2005
7,063
Isolated the diode and it is functioning properly. That was my last hope for trying to figure out why my GPS charger shows power on the charger and GPS and yet doesn't charge the GPS battery.
Oh well, off to get a new charger.
Thanks to all for the help
Are you sure the battery is good?
 
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