In need for a fast relay (SSR?)

Discussion in 'General Electronics Chat' started by Olivier Beaudoin, Oct 7, 2014.

  1. Olivier Beaudoin

    Thread Starter New Member

    Oct 7, 2014
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    Capture.PNG

    Hi guys and gals!

    I have a problem here... And I tought that you could possibly help me!

    I have a project where I need to apply a certain voltage (0 to 300VDC) to a resistive load for a given amount of time and then drop the voltage to zero (single shot voltage burst). So in short, I need a relay! But the problem is that I need it to be very fast and high voltage (up to 300VDC). Right now, I use a Crydom DC400D10. It is good for relatively long burst (200us and up) but I cant get lower that that due to principally "toff" delay and rising and falling time.

    You can see here (on top) in that shot (1200us corrected on the output voltage, the signal is shorter to take into account the ton and toff) that the toff delay is pretty long.

    I can live with "ton" delay as what I really measure is the total energy but the rising and falling times and "toff" are really killing it.

    What I really would like to have is something in the order of 10us. I dont know if you know any SSR that is capable of that?

    Thanks for your advices!

    (sorry about my english, not my first language)
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Olivier Beaudoin likes this.
  3. Olivier Beaudoin

    Thread Starter New Member

    Oct 7, 2014
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    Darlington_Spice.jpg

    Thanks for the idea!

    I have been looking at Darlington for some days now and I think I have found a nice solution. The "lag" is greatly reduce if the simulation is right (less thann 5us for 150V output). The parts in the LTSpice simulation is not the ones I will be using because I need to go to at least to 250V (I will be using a MJ11021 for the Darlington and a PZTA42 for the NPN)

    250Vce for a PNP darlington seem to be the max?

    I have made some rough calculation, maybe I'm completly wrong... I would like the switch to be working from 10V to 250V

    Have I missed something obvious?

    Thanks again!
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    If your Vmax is 250V then you should choose the Vceo of bjt is great than 1.5 times about 375V, at least it has 1.2 times as 300V.
     
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