Relay Suppression Diode Failure

Mark P · 2007-06-18T19:36:03+00:00

I trying to determine the cause of a relay suppression diode failure.The diode is built into the relay can (T-05 type) and is a standardswitching type diode - according to the manufacturer. The relay coilspecs: L=600mH and R=850 ohms. The relay was driven with a 2 secondON pulse followed by 2 seconds OFF. This duty cycle was continued forthree minutes. The relay was driven with a transistor switch on thelow side. The voltage on the coil was 13V. The relay failed and afterit was opened up you could see that the diode was cooked. When the transistor switch turns OFF the diode suppresses the voltagetransient. Is there sufficient energy dissipated in the diode over 3minutes to cause it to fail? Is there a way to calculate or estimatethe diode junction temp rise? The manufacturer has no thermal data onthe part.

Jun 18, 2007 21 Replies

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Spehro Pefhany 19 years ago

I doubt that a modern ohmmeter will develop enough voltage across a TO-5 relay coil to forward bias the diode. The OP said 850R, so it would have to push 0.7mA through the coil. More practically, I suspect full scale (except on the diode scale) is typically 200mV.

Best regards, Spehro Pefhany

"it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

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Jim Thompson 19 years ago

Sno-o-o-o-o-ort ;-)

...Jim Thompson

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