LED Tester

Dear All,

I am now working on design of a PCBA Tester. The PCBA I am going to
test has a few LEDs. After assembly process, we will design a test
station where the LED in PCBA will be checked for open/short/reverse
polarity.
The basic concept of the design include pumping in the current into
LED via USB connector power supply (hope I could use up to 500 mA).The
idea is to use USB connector from PC as a power supply to pump in the
current
into the LEDs. There, I will add a 50 ohm resistor between the cathode
of the LED and the 5 V USB Gnd. The voltage will be read from the LED
to determine its condition.
Practically testing it, if the LED is worngly mounted in reverse
polarity, at least 50 mA is sinking into the PCBA. I wish to know
whether this amount would do any harm to the PCBAs.
Can anybody give me some advice on this?
please help. I am also looking for alternative ways.

Regards

 

Thanks for your kind respond.

What would you like to mean by grabbing 500 mA is not compilant with
USB specs?

I know that it limits the current up to 500 mA. We are using just a
few mA round about 100 mA maximum. This won't create any problem,
will it?

 

Thank you so much for your kind explanation joel and michel.

I am thinking of testing LEDs installed DUT with automated test
station.

I will pump current into the LEDs and read out the voltage. If it is
not shorted, open circuited or reversely installed, it will give
readings in acceptable range and it will pass the test.

I think it is a feasible solution for it. What i am worried is that at
least 16 mA will be sinking into the DUT circuit.

I hope 16 mA sink current into the PCBA when there is no power
supplied won't damage the PCBA nor degrade any component in the PCBA
because of this test.

Any suggestions?

Thanks