Re: Aw: Re: Re: Re: AW: [EVGRAY] Re: "Impressive"!

Body

Hi Sven,

To turn off the thyristor the current just has to be prevented from going through the thyristor. This can be done by discharging a capacitor across the anode-cathode legs to make the current go through the capacitor for a brief moment of time. This is class C and D here: https://www.electronicshub.org/scr-turn-off-methods/ https://www.electronicshub.org/scr-turn-off-methods/

A transistor can be used as a switch to discharge the capacitor instead of a second thyristor. If using a transistor directly in parallel to the thyristor the transistor has to have much less conduction resistance than the SCR which makes the transistor probably better as a switch instead of the SCR.

Regards
Ole


---In [email protected], <s.friedrich@...> wrote :

 Hello Ole, that's right, but how do I turn it off faster? I have already looked at everything with SCR Commutation. The only thing I think that can work is a capacitor in series at the cathode and a bleeder resistor in parallel, so I'll change the whole signal and bring an additional active share.
 
 regards
 
 Sven   Gesendet: Freitag, 02. März 2018 um 18:22 Uhr
 Von: "onielsen@... [EVGRAY]" <[email protected]>
 An: [email protected]
 Betreff: Re: Aw: Re: Re: AW: [EVGRAY] Re: "Impressive"!
   Hi Sven,
 
 This only works if the current through the thyristors are stopped from outside the thyristors by diverting the current around the thyristors for long enough time to remove the charge carriers in the crystal inside the thyristors. The diode then will prevent the destructive flyback voltage. If waiting until the thyristors automatic shut off there is no more current (magnetism) in the inductors and thus no flyback voltage is generated. Thus the diode protection can be omitted.
 
 Diode protection is only necessary if shutting off the thyristors faster than they do when left alone.
 
 Regards
 Ole
 
 
 ---In [email protected], <s.friedrich@...> wrote :
  
 Hi Ole,
  whether this really works with thyristors, which only switch off when no or little current flows. I can not imagine that this will switch off faster as long as there is still energy flowing. The modern semiconductors are shut down so that the energy can then flow into the inductor.
 
 regards
 
 Sven   Gesendet: Freitag, 02. März 2018 um 00:26 Uhr
 Von: "onielsen@... [EVGRAY]" <[email protected]>
 An: [email protected]
 Betreff: Re: Aw: Re: AW: [EVGRAY] Re: "Impressive"!
   Hi Sven,
 
 "how should I short-circuit the inductors?
 
 With a magnetic shunt or semiconductors?"
 
 A diode reverse biased in parallel with the inductor will delay demagnetization of the inductor. See left side of the image.
 
 The image is copied and pasted from here: https://electronics.stackexchange.com/questions/31014/where-should-i-put-the-kickback-diode-in-a-transistor-switch https://electronics.stackexchange.com/questions/31014/where-should-i-put-the-kickback-diode-in-a-transistor-switch
 
 As the diode as well as the inductor both have resistance the energy is dissipated as i^2 x R heat. But it does prevent the energy being released as a high voltage flyback pulse or actually it is a very slow pulse of low voltage. The voltage is only the voltage across the diode in forward conduction mode. If the inductor is the coil of a relay this method makes the relay release much slower. For a fast release (dissipation of the stored energy) a resistor can be used to dissipate the energy at a much faster rate. As the current at shut off is known the resistance can be chosen to limit the voltage to a level just below the max rating of the semiconductor. U=IR where U is the voltage I is the current and R is the resistance.
 
 Regards
 Ole
 
  
 
 
 ---In [email protected], <s.friedrich@...> wrote :
   Hi Ole,
 
 how should I short-circuit the inductors?
 
 With a magnetic shunt or semiconductors?
 
 regards
 
 Sven   Gesendet: Donnerstag, 01. März 2018 um 13:22 Uhr
 Von: "onielsen@... [EVGRAY]" <[email protected]>
 An: [email protected]
 Betreff: Re: AW: [EVGRAY] Re: "Impressive"!
   Hi Sven,
 
 "I want to turn off the scr faster and use no fets."
 If forcing them to disrupt the current through the inductors flyback pulses are generated unless shorting the inductors. Actually shorting the inductors would be a way to divert the current from the the SCRs to make them turn off. Then the current stays in the inductors as a magnetic field. I.e  this make the inductors permanent magnets.
 
 Regards
 Ole
 
  
 
 
 ---In [email protected], <s.friedrich@...> wrote :
    
 Hi Mick, with adjustable inductance a variac to work for any diode plug. I want to turn off the scr faster and use no fets. Greetings Sven
  
 Von Samsung Mobile gesendet
 
 
 
 -------- Ursprüngliche Nachricht --------
 Von: "mkjekyll@... [EVGRAY]"
 Datum:01.03.2018 08:22 (GMT+01:00)
 An: [email protected]
 Betreff: [EVGRAY] Re: "Impressive"!
 
   Sven,
  
 I don't recall if you are using the diode plug with the inductor or without.  
 You want to switch fast here is something:
 http://www.ti.com/lit/ds/symlink/uc1710.pdf http://www.ti.com/lit/ds/symlink/uc1710.pdf