AUXILIARY TURNOFF CIRCUIT FOR A THYRISTOR SWITCH

• US 3,585,403 A
• Filed: 09/24/1968
• Issued: 06/15/1971
• Est. Priority Date: 09/24/1968
• Status: Expired due to Term

• Current Assignee: John G. Gribbons
• Original Assignee: John G. Gribbons
• Inventors: Gribbons, John G.
• Application Number:
  US04/761,980
• Time in Patent Office: 994 Days
• US Class Current: 327/471
• CPC Class Codes: H02M 1/06 Circuits specially adapted for rendering non-conductive gas discharge tubes or equivalent semiconductor devices, e.g. thyratrons, thyristors

Abstract

An auxiliary turnoff circuit for a thyristor switch string in which a normally open switch, connected across at least one of the thyristors in the string, is caused to repeatedly close should the string permanently latch on. The first closure is timed to occur after the automatic turnoff circuit has failed to open the switch string and the closed intervals are greater than the normal recovery time of the thyristors in the string.

Claims

1. An auxiliary turnoff circuit for a thyristor switch circuit of the type having a string of thyristor switches connected in series and an automatic turnOff circuit for opening the switch circuit a timed interval after its closure, said auxiliary turnoff circuit comprising a normally open switch connected across at least one thyristor switch of said string, and means connected to said string of thyristors and responsive to a drop in voltage thereacross for repeatedly closing said normally open switch, the time period between successive ones of said repeated closings being greater than the timed interval of said automatic turnoff circuit while the time of each closing exceeds the normal recovery time of said thyristor switches.

2. The combination of claim 1 wherein said normally open switch comprising at least one transistor having a collector electrode connected to the anode of one of said thyristor switches and an emitter electrode connected to the cathode of the same thyristor switch.

3. The combination of claim 1 wherein said means connected to said string of thyristors for repeatedly closing said normally open switch comprises a timing circuit of a resistance means connected in series with a capacitor, means for alternately and repeatedly charging and discharging said capacitor through said resistance means in response to a drop in voltage across said thyristor string, and means connecting said capacitor to said normally open switch to close said switch each time said capacitor is charged.

4. An auxiliary turnoff circuit for a series string of thyristor switches subject to permanent latch on due to radiation or other causes maintaining conduction in said switches beyond their normal automatic turnoff time, said auxiliary turnoff circuit comprising a normally open switching means connected across at least one thyristor switch of said string, a voltage sensing means connected to said string deriving a voltage therefrom proportional to the voltage across the string, means coupling said voltage sensing means to said normally open switching means for repeatedly closing said normally open switching means as said derived voltage drops below a predetermined limit, the first of said closures occurring after the drop of said derived voltage a period of time greater than said normal automatic turnoff time while the closure time exceeds the normal recovery time of said thyristor switches.

5. The combination of claim 4 wherein said normally open switch comprises at least one transistor having a collector electrode connected to the anode of one of said thyristor switches and an emitter electrode connected to the cathode of the same thyristor switch.

6. The combination of claim 4 wherein said means coupling said voltage sensing means to said normally open switching means comprises a timing circuit of a resistance means connected in series with a capacitor, means for alternately and repeatedly charging and discharging said capacitor through said resistance means, and means connecting said capacitor to said normally open switching means to close said switch each time said capacitor is charged.