Safety relay replaced by Solid State (MOSFET)

Jan 25, 2011 4 Replies
K

Hi



I am involved in a project where we may be looking towards using solid state (MOSFETs) to energize a 3phase motor or in another case just a simple solenoid.



But, it is unclear precisely which rules apply and if it is possible to use solid state to control a motor in a safety critical application. Also if the use of a SIL3 approved solid state solution would allow us to remove a safety breaker in front of the electronics if the electronics are designed accordingly (with doubled current sense circuits to act as over current guard)



Do any of you guys have input to this or a direction for me to search for answers to this?



Thanks



Klaus


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M

Most likely you will need a mechanical break connection (actually 2) if it is a safety function for SIL3. Best to look into the standards you need to meet. Interesting reading..

Cheers

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M

The typical failure mode of most power semiconductors to to fail short, unless there is sufficient power available to physically blow them apart .

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W

Am 26.01.2011 00:36, schrieb Klaus Kragelund:

Mosfets, IGBTs and whatever are typical rated for maximum di/dt, du/dt. Using proper protection against that using chokes and capacitors would be a good starting point. Having two independant circuits with two solid state circuits in series

- designed _after_ reading the datasheet - and tested for compliance should be a good starting point. A SIL3 approved solid state solution would only work approved within its limits...

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