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Solid States Devices => solid state devices => Topic started by: Belinga on January 15, 2018, 10:38:38 AM

Title: Would this be a good solid state solution to measure the inrush current?
Post by: Belinga on January 15, 2018, 10:38:38 AM

I've a problem where I need to measure the inrush current of some parallel DC/DC converters in a system where the input voltage may vary between 360-600Vdc on start up. The inrush current is roughly estimated to peak around 500A for a short duration before settling for a max current on around 15A.

I've previously tried with a mechanical relay however that particular relay, bounces on and off before making a solid contact making me unable to make an reliable measurement. Therefore I need a solid state switch solution.

The measurement is done by a current probe , P6303.


Despite my non previous experience of thyristors my idea is to solve this with the use of a thyristor. I think that I in this way will get a faster and less noisy switch than the mechanical relay.

At the moment I've a MCD56-12io8B thyristor( ( laying around,which I think I can use as followed:

(See attachment Rqzsf.png)

I have also thought of skipping the SW in the circuit and just turn on the Voltage of Vc, directly from the bench supply and hope it doesn't exceed the Vgc max.

I know that in this configuration I will only be able to turn on the thyristor however this is not a problem. I will just turn off the supply (vin) for that.

I guess the low-side solution would be easiest and safest. However I'm a bit unsure what will be the maximum allowable gate voltage for the thyristor. I can't find Vgc max or any equivalent in the datasheet to what "vgs max" is called for mosfets, which I'm familiar with, but I guess if i'm below 4V it will be chill. If you look at the pic below from the datasheet fig 5

(See attachment L5W4z.png)

Right now I would set the gate voltage to slightly above the gate trigger voltage, and the current through the gate to a value above 100mA

(See attachment cuJ7y.png)
May this be a good solution to my problem or should I just buy an expensive ready made solid state solution..