0
\$\begingroup\$

enter image description here

When simulating this circuit in Proteus, I expect the LED to light up when the switch is closed, but it does not light up. What am I doing wrong?

\$\endgroup\$
  • \$\begingroup\$ What happens when you short drain to source? \$\endgroup\$ – Andy aka Oct 17 at 18:18
  • 1
    \$\begingroup\$ The circuit should have to work. Move Q2 to the right and double-check if its gate s really connected. \$\endgroup\$ – Huisman Oct 17 at 18:19
  • \$\begingroup\$ @Huisman I checked and it is connected. \$\endgroup\$ – muyustan Oct 17 at 18:21
  • \$\begingroup\$ @Andyaka could'nt get what you mean \$\endgroup\$ – muyustan Oct 17 at 18:22
  • \$\begingroup\$ @muyustan Andy is saying to bypass the transistor, put a wire from drain to source of the FET. \$\endgroup\$ – KingDuken Oct 17 at 18:39
0
\$\begingroup\$

I don't understand if this is a physical circuit or a simulation.

For starters, you're supplying a relatively low current to the LED, about 7mA. I suspect this is too low, but also that you should see it glow dimly when on.

\$\endgroup\$
  • \$\begingroup\$ I have constructed this circuit before with real components and it was working, now I am at home and wanted to try it on a simulation but didn't work now, so wondered if I am doing something different than it should be. \$\endgroup\$ – muyustan Oct 17 at 18:32
  • \$\begingroup\$ 7mA is more than enough to light a modern indicator LED, in my experience. It'll be dimmer than at full operating current but bright enough to see without having to shade it with your hand or anything. \$\endgroup\$ – Hearth Oct 17 at 18:32
  • \$\begingroup\$ @Hearth , Yes, a few mA should do for a modern indicator LED, but we have no idea what the OP is using. \$\endgroup\$ – Scott Seidman Oct 17 at 18:36
  • 1
    \$\begingroup\$ The Proteus simulator may be looking for a certain current before lighting the LED. Try reducing R2. \$\endgroup\$ – rdtsc Oct 17 at 19:37
0
\$\begingroup\$

The circuit should work, so the possibilities are

1) a bad component (FET, LED),

2) a wiring mistake, or

3) a wrong value resistor (1M instead of 1k for R2 for example.)

A small LED should show some emission with 5-10mA, but maybe your LED needs more current to glow brightly.

\$\endgroup\$
  • \$\begingroup\$ I have constructed this circuit before with real components and it was working, now I am at home and wanted to try it on a simulation but didn't work now, so wondered if I am doing something different than it should be. \$\endgroup\$ – muyustan Oct 17 at 18:32
  • \$\begingroup\$ OK, since you didn't specify this answer assumed a real circuit. Now that we know it's a simulation you should check the LED model to see how much current it needs to light. Remove the LED and see if the FET switches normally and if the current through R2 is what you expect. If so, it's the LED model. \$\endgroup\$ – John D Oct 17 at 19:58
  • \$\begingroup\$ thanks, I will try and let you know \$\endgroup\$ – muyustan Oct 17 at 20:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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