Component Failures

Electronic components can fail in many ways. Here I try to document some failures that I've encountered.

Resistors usually fail open. I had a small gate resistor failed open, but I'm not sure if it failed because of a surge of current or a spike in voltage. I had an SMT 0805 resistor rated for 100V failed when 200V was applied to it. It failed slowly; I knew that because it was connected to an LED, and the LED faded and flicked a little before completely went out.  A current surge on a resistor may just change its resistance.  I had one current sense resistor increased its resistance by a factor 2 and another changed a few percent after current surge.  Another 50-milliOhm axial current sensing resistance increased resistance to 250milliOhms.

An aluminum can capacitor blew itself apart completely after it was applied with reverse polarity voltage. A 1000uF 16V aluminum electrolytic capacitor at the output of 5V 2.5A AC adapter appeared overheated and failed with reduced capacitance.   A ceramic capacitor fails short.  It happened on a cPCI power backplane, which had a 10uF ceramic cap on 12V and became a 4-Ohm short.

A diode in a PC power supply failed short, tripped the fuse.

A white LED was overstressed with larger than normal current for a long time.  It did not fail completely; but it flickered.  It ran fine with reduced current.

Power MOSFETs can fail short. Usually a check for the resistances between terminals if the MOSFET is alive; all should be high impedance except that the source-drain body diode may give a little lower reading (depending on the meter used) if measured in the forward polarity of the diode. A check of the source-drain body diode voltage is also a good test; it should be about 0.5V (also depending on the meter used) in the forward direction and no voltage in the other direction. I had a power MOSFET in a push-pull converter failed with a source-drain hard short and gate-source short with 420 Ohms resistance. It was probably killed with a surge of current possibly due to transformer magnetic saturation. Another one died with the body diode still intact. But there was finite resistance between the gate and drain; when it was powered, it simply shorted the drain and source. An examination of its TO-220 casing showed blisters on the metal tab.

Opamps can fail when the output is shorted. Some opamps are more resistant to output short. The output stage is destroyed when the output is shorted and excessive current flows. I had a gate driver failed when the output was shorted to the ground. The damaged IC had the supply pins shorted as well as the output pin shorted to the supply pins.

Inductors and transformers are not easily destroyed, but they can wreak havoc on the components connected to them.  Enormous voltages can be readily generated when they are switched.