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The following is a circuit I have tried simulating on multisim. The LED on the transmitter part does not light up. The current is 0 through that LED. Is it legitimate? enter image description here

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    \$\begingroup\$ What's the circuit supposed to do? \$\endgroup\$ – EM Fields Dec 1 '14 at 19:12
  • \$\begingroup\$ Which way round do you have D1, the LED? The symbol is just a dot, with no indication of polarity. \$\endgroup\$ – John Honniball Dec 1 '14 at 19:31
  • \$\begingroup\$ Can you give a link to the article on Electyronics Hub that discusses this circuit? \$\endgroup\$ – Peter Bennett Dec 1 '14 at 20:18
  • \$\begingroup\$ The second circuit is missing a connection from the D3/D4 junction to the "GND" pin of U1. \$\endgroup\$ – markrages Dec 1 '14 at 20:35
  • \$\begingroup\$ Also, note that there's a wire missing from the anodes of D3, D4 to the GND of U1, in the receiver circuit. Edit: Bah! Too late! \$\endgroup\$ – John Honniball Dec 1 '14 at 20:58
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The LED probably doesn't illuminate because there is virtually no voltage across it (both ends at about 30V) but that's not the main problem.

The transmitter schematic shows you are applying almost Vgs=30V to the gate of a FET with Vgs absolute maximum of +/- 20V.

You almost certainly need to replace the FETs, as well as rethink the gate drives to the circuit.

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R3 is 94 ohms, and in parallel with the LED and R1. You would get at best 0.3V across the diode and R1 combined. Combined with the 1kΩ of R1, and you're not going to really see any significant current.

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  • \$\begingroup\$ I make the voltage across R3 0.282 volts - far from enough to allow the LED to make any light. \$\endgroup\$ – Peter Bennett Dec 1 '14 at 19:50
  • \$\begingroup\$ @PeterBennett That's what I get for trying to look at it on my phone. It looked like 1kΩ, but now I can (barely) see that R2 is in fact 10kΩ. \$\endgroup\$ – W5VO Dec 2 '14 at 0:02
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A typical LED has a forward voltage drop of about 2V for normal operation, which leaves around 28V (30-2) on the R1,R2 resistors, which gives 28/(1K+10K) = 2.5mA current flow, which is not enough for typical LED for normal operation. Check your LED parameters, and match the resistors accordingly.

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    \$\begingroup\$ 2.5mA is plenty to make a LED light up, it just won't be at full intensity. \$\endgroup\$ – W5VO Dec 1 '14 at 18:53
  • \$\begingroup\$ @W5VO Basic LEDs are rated for around 20mA. 2.5mA is way lower than that. Once again, it should be checked with the part's model. \$\endgroup\$ – Eugene Sh. Dec 1 '14 at 18:58
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    \$\begingroup\$ @EugeneSh.: the typical 20 mA rating for common LEDs is normally the recommended maximum current. They will work fine at much lower currents. \$\endgroup\$ – Peter Bennett Dec 1 '14 at 20:16
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Your bridge rectifier is not wired correctly, D3 and D4 should not be in series, and there's no connection from your bridge rectifier to the rest of the circuit's ground.

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    \$\begingroup\$ There's no point worrying about the receiver circuit yet... \$\endgroup\$ – Brian Drummond Dec 1 '14 at 21:12

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