0
\$\begingroup\$

I implement following circuit

enter image description here

I used 12v alarm instead of led at high side.

I used two 5.6k Ω resistor (blue) at place of Rg and 330 Ω resistor in place of R1

I used the same IRF630 n-channel mosfet

45 white row is + 12V

62 orange row is 12V GND

17 yellow row is +5 V

Alarm doesn't ring

enter image description here

I tested alarm at series 12 V circuit with 330 Ohm resistor without mosfet and it ring properly

Edit: measured voltages at leads:

Vds: 1.1V

Vgs: 0 V

Edit:

if I connect gate to +12 V alarm rings, at such configuration gate-source is 11.8 V

\$\endgroup\$
11
  • 1
    \$\begingroup\$ The 12 V alarm probably doesn't want a resistor in series with it. But no way to know unless you link to the datasheet for the alarm. \$\endgroup\$
    – John D
    Sep 22, 2023 at 17:15
  • \$\begingroup\$ I tested alarm at series12 V circuit with 330 Ohm resistor without mosfet and it ring properly \$\endgroup\$ Sep 22, 2023 at 17:18
  • \$\begingroup\$ Are you really using an IRF630 and driving with 5 V? The threshold can be as high as 4 V, so you may not be turning the FET on hard enough. Measure the drain voltage while you're trying to turn the FET on and see what you get. \$\endgroup\$
    – John D
    Sep 22, 2023 at 17:45
  • \$\begingroup\$ It looks okay (typically, you've not really got enough gate voltage for that MOSFET to switch fully on worst case). Maybe one of your jumper wires is open. Measure the two voltage at the MOSFET gate and drain relative to the source, right at the TO-220 leads, and tell us what readings you get. \$\endgroup\$ Sep 22, 2023 at 17:50
  • 3
    \$\begingroup\$ Connection between 5 V GND and 12 V GND is missing. \$\endgroup\$
    – Jens
    Sep 22, 2023 at 22:22

1 Answer 1

1
\$\begingroup\$

Connection between 5 V GND and 12 V GND was missing

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.