Hi,
We are using an MPSA42 NPN transistor (TO-92) package in a product to drive a string of 30 blue LEDs from 120 VDC through a dropping resistor. Occasionally, one of our products is returned to us by our customer with the failure mode "blue LEDs not illuminating." When we inspect the unit, we see that the corner of the TO-92 package that is closest to the emitter has broken off (see photo). Further, the transistor is "intermittent" in that we can press on it (i.e. physically move the transistor very slightly) and the circuit will begin to work again. I think that the customer is applying too much voltage to our circuit and that is causing the case to "pop". Does this make sense? It certainly appears to me to be caused by electrical stress (exceeding the Absolute Maximum Ratings of the MPSA42) and not physical stress. Any comments would be appreciated!
Thanks,
Mike
We are using an MPSA42 NPN transistor (TO-92) package in a product to drive a string of 30 blue LEDs from 120 VDC through a dropping resistor. Occasionally, one of our products is returned to us by our customer with the failure mode "blue LEDs not illuminating." When we inspect the unit, we see that the corner of the TO-92 package that is closest to the emitter has broken off (see photo). Further, the transistor is "intermittent" in that we can press on it (i.e. physically move the transistor very slightly) and the circuit will begin to work again. I think that the customer is applying too much voltage to our circuit and that is causing the case to "pop". Does this make sense? It certainly appears to me to be caused by electrical stress (exceeding the Absolute Maximum Ratings of the MPSA42) and not physical stress. Any comments would be appreciated!
Thanks,
Mike