Electronic – Crowbar circuit and choice of the SCR

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I am building a Crowbar circuit for one of my sensor which is power supplied through a Recom Power R-785.0-0.5 (datasheet).
The crowbar SCR is controlled by this IC.

I am having troubles in selecting the right SCR because:

  1. I don't understand what happen at the output of the R-785.0-0.5 when the CC happens. The datasheet says that it has short circuit protection, but what does that mean?
  2. What is the maximal current which will go through the SCR when short circuited?
  3. What is the output current limit of the R-785.0-0.5 of 2000mA in the datasheet?

Any suggestion for a correct SCR?

Best Answer

I don't understand what happen at the output of the R-785.0-0.5 when the CC happens. The datasheet says that it has short circuit protection, but what does that mean?

The clue is when it says: -

Short Circuit Input Current (Vin = 24V) All Series 60mA

This means that if you short the output the internal circuits of the device prevent a current of greater than 60mA flowing into the device and this is usually called fold-back protection. Basically when the output is shorted the output current is rapidly reduced to below (say) 100mA.

What is the maximal current which will go through the SCR when short circuited?

I estimate no more than 100mA but there is a doubt that it could be higher. It's a pity the data sheet doesn't explicitly state this.

Regards the SCR virtually any listed on page 6 of the ON semi data sheet would do and probably quite a few that are much smaller.