Like in a scr say in thyristors or triacs we know we can turn the scr "on" after a certain anode-cathode break-over voltage depending on the current present at the gate.But I want to know whether there is device or circuit which remains off if the applied voltage is greater than the specified voltage value according to the device and it will turn "on" if the applied voltage goes below that of pre-specified voltage value. In other word its a reversed-functioned SCR. (I do not care whether it is unidirectional of bidirectional)

  • \$\begingroup\$ sounds like a negative-resistance device. Only one I can think of is a normally-open relay. \$\endgroup\$
    – glen_geek
    Mar 1, 2021 at 15:41
  • \$\begingroup\$ but can we switch standard 60hz ac through it? seems to be impractical \$\endgroup\$
    – Sayan
    Mar 1, 2021 at 15:44
  • 1
    \$\begingroup\$ This function does not exist as a part but it can designed as a self biased latch \$\endgroup\$ Mar 1, 2021 at 16:00

1 Answer 1


JFETs and depletion-mode MOSFETs have the characteristic of being "on" with no voltage applied and they will turn "off" when a negative voltage is applied to the gate (N-channel devices).

They do not, however, have the "latching" characteristic of thyristors. Available devices are also fairly limited in current-handling capability, in the 10A range, and higher voltage devices are capable of much less current.

  • \$\begingroup\$ but A JFET can't handle much current, if I am aiming to drive a load say, of 2A \$\endgroup\$
    – Sayan
    Mar 1, 2021 at 16:05
  • 1
    \$\begingroup\$ Then use a depletion mode MOSFET. Eg. IXTT16N10D2. You can search for others that might meet any additional requirements you might have. \$\endgroup\$ Mar 1, 2021 at 16:06

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