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I have a small DC current requirement of less than 30mA @ 24V DC from 230V AC main source. Instead of using an expensive transformer based power supply I am trying to implement a low cost voltage dropping capacitor based power supply.

I understand how fatal it can be due to non-isolation so the enclosure will be completely sealed so the end user cannot touch any part unless he breaks enclosure start poking around it.

As a first step I am trying to simulate a 5V output as suggested in this link. I tried something similar in Proteus but my simulation is giving a different result:

  1. No current is flowing through the LED when the switch is in the ON postion
  2. Voltage is not going back to zero (0) when the switch is in the OFF position.

enter image description here

Can someone please let me know where am I wrong in the simulation?

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    \$\begingroup\$ Why do you think its wrong? Maybe add a reference ground node to the anode of D2. \$\endgroup\$
    – Andy aka
    Dec 1, 2021 at 14:33
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    \$\begingroup\$ It turn out to be the issue with LED model selected as digital (default in proteus 8). Once LED selected as Analog it is working as expected. \$\endgroup\$
    – Gailu
    Dec 4, 2021 at 7:10
  • \$\begingroup\$ How can the simulation work when the input vSINE has no voltage and no frequency?? \$\endgroup\$
    – Audioguru
    Mar 9, 2023 at 0:15

1 Answer 1

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First thing is the ammeter. As can be seen, it measures in Amps. If the current is less than 5mA it'll show zero. Because, for example, rounding 0.004 up will give 0.00. But rounding 0.005 will give 0.01.

Another thing is the LED. Its nominal current, specifically. If the LED's nominal current is set to 10mA (it is by default), it'll not illuminate if the current flowing through it is less than this.

Judging from the values seen on the simulation, the voltage level is normal but the current is quite low.

So,

  • Change the ammeter range to milliamps. Double click on it, a properties window will appear. The rest is simple and obvious.
  • Decrease the LED's nominal current. Double click on it, a properties window will appear. The rest is simple and obvious.

Also check the components' values/properties and the interconnections.

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