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Vacuum relay vs solid state I have an unusual circuit that needs to be designed. What I need to do is mimic two 12volt relays ( in principal anyway ) to control an ac source. The source goes to the common terminals of the two relays. When the relays are energized the ac flows out of the normally open terminal. When at rest the ac source then flows out of the normally closed terminal. This all has to be performed at a rather high rate of speed ( about 20 kHz ). Also the source is high voltage about 2000 volts and about 30 amps. I was considering using a DPDT vacuum tube relay, it will easily handle the voltage and the current.. However they are not designed to switch at a high rate of speed continuously. This is my dilemma. I would like to go solid state but I'm not sure that it is possible. This is going to require a VERY clever individual. Any thoughts?    

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    \$\begingroup\$ Why do you need to do this? Maybe there is a better way. \$\endgroup\$
    – Thomas O
    Nov 20 '10 at 9:23
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    \$\begingroup\$ I don't think any relay can switch at 20 khz. \$\endgroup\$ Nov 20 '10 at 12:46
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    \$\begingroup\$ 2 kV × 30 A = 60 kW...don't know what it is but it sounds fun. \$\endgroup\$
    – Nick T
    Nov 20 '10 at 18:13
  • \$\begingroup\$ What is the frequency of your AC, I have a suggestion, but my solution only turns off when the AC switches direction. \$\endgroup\$
    – Kortuk
    Nov 21 '10 at 16:12
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IGBTs would probably be the switching element of choice at this level of power and voltage.

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  • \$\begingroup\$ Here's a good IRF whitepaper on MOSFET vs. IGBT (PDF) which recommends IGBT for applications above 1 kV. It is somewhat old and MOSFETs have creeped higher in voltage, and it doesn't bother to mention other technologies (as IRF doesn't make them) \$\endgroup\$
    – Nick T
    Nov 20 '10 at 18:20
  • \$\begingroup\$ I would suggest and IGBT as a good choice. I like SCRs a lot, but I am not sure that switching frequency would bode well. \$\endgroup\$
    – Kortuk
    Nov 21 '10 at 22:20

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