LED indicator on AC

[Watth]

I have been experimenting with the LED circuit.
This solution is for the primary (230V AC)

https://www.falstad.com/s.php?s=DpX00P

I get about 5 mA on the LED, and a little less than 500 mW ont he resistor.

Does it make sense?
I will adjust the values for the secondary side.

[Gyro]

I'm puzzled by the responses here about using a neon bulb.
A neon light is quite a bit dimmer than just about any LED, so it should be perfect for your purpose.
All you need is a current-limiting resistor. Put it on the 230-volt side.

Yes, you are confused.

It is incorrect to say that Neons are dimmer than LEDs. You can't adjust the brightness of a Neon, up or down, without either shortening its life or turning into a distracting flickering mess. An LED's brightness can bee adjusted anywhere from its  maximum specified brightness right down to zero.

[Gyro]

I have been experimenting with the LED circuit.
This solution is for the primary (230V AC)
(Attachment Link)
https://www.falstad.com/s.php?s=DpX00P

I get about 5 mA on the LED, and a little less than 500 mW ont he resistor.

Does it make sense?
I will adjust the values for the secondary side.

You should be able to get sufficient brightness at 1mA with a modern LED, especially if you want it dim. I would put the resistor on the AC side of the bridge, this will minimise the required PIV of the diodes, allowing you to use small 1N4148s. Personally I would lose the 10uF capacitor - the resulting 100Hz flicker will be imperceptible compared to the half wave rectified version.


P.S. I would adjust the 100nF capacitor value downwards for reducing the LED brightness rather than having such a high value (and resulting heat dissipation) resistor.

[Watth]

So here is the new circuit:
230V

https://www.falstad.com/s.php?s=rZBDlJ
R dissipates 170 mW

55V

https://www.falstad.com/s.php?s=Etipqr
R dissipates 84 mW

In both cases, current in LED is about 1.7mA

Now I am looking at diodes, and I am considering bridge rectifier to simplify connections and layout, as it will for now be assembled as a dead bug circuit.
For example: Bridge rectifier: single-phase; 800V; If: 0.5A; Ifsm: 35A https://www.tme.eu/Document/8fc49bd76b76ff3a03de43cc393d0385/MB2M-MB10M.pdf

[Gyro]

That looks more like it, dissipation wise.

Now I am looking at diodes, and I am considering bridge rectifier to simplify connections and layout, as it will for now be assembled as a dead bug circuit.
For example: Bridge rectifier: single-phase; 800V; If: 0.5A; Ifsm: 35A https://www.tme.eu/Document/8fc49bd76b76ff3a03de43cc393d0385/MB2M-MB10M.pdf

Yikes! You don't need anything like that. The output voltage, and therefore the input voltage, of the bridge is clamped by the forward voltage of the LED, so it won't see any high voltages. That's why moving the resistor to the AC side of the bridge was a good idea.

If you really don't want to put 4 x 1n4148s on a piece of stripboard (together with the cap and resistor in the 55V case - you want to be a bit more careful with the mains version), then you can get little bridge rectifiers in 4 pin DIP packages*.


Edit: 1 just  did a double take. A resistive drop of 55V (ignoring the drop of the bridge and LED) at 2mA is only 110mW. The cap is doing nothing for you. Just use a resistor. I wouldn't use the mains version, I don't think you're ready for that, safe construction wise (using dead bug for it).

* Sorry, the 800V and I_FSM threw me, I didn't realize you link was for a 4 pin DIP.

[OldBeginner]

A voltage doubler can be used to power the neon bulb in the secondary circuit.
What is the voltage drop across the emergency resistor? Could it be used to power an LED?

[Watth]

That looks more like it, dissipation wise.

Now I am looking at diodes, and I am considering bridge rectifier to simplify connections and layout, as it will for now be assembled as a dead bug circuit.
For example: Bridge rectifier: single-phase; 800V; If: 0.5A; Ifsm: 35A https://www.tme.eu/Document/8fc49bd76b76ff3a03de43cc393d0385/MB2M-MB10M.pdf

Yikes! You don't need anything like that. The output voltage, and therefore the input voltage, of the bridge is clamped by the forward voltage of the LED, so it won't see any high voltages. That's why moving the resistor to the AC side of the bridge was a good idea.

If you really don't want to put 4 x 1n4148s on a piece of stripboard (together with the cap and resistor in the 55V case - you want to be a bit more careful with the mains version), then you can get little bridge rectifiers in 4 pin DIP packages*.


Edit: 1 just  did a double take. A resistive drop of 55V (ignoring the drop of the bridge and LED) at 2mA is only 110mW. The cap is doing nothing for you. Just use a resistor. I wouldn't use the mains version, I don't think you're ready for that, safe construction wise (using dead bug for it).

* Sorry, the 800V and I_FSM threw me, I didn't realize you link was for a 4 pin DIP.

Again, thanks for the feedback.

As for the deadbug thing, the project will be enclosed, every wire will be in heatshring sleeves, components will be fixed in the enclosure so that they don't create unwanted connection, every thing goes through a fuse. As it is a one shot project, I am not inclined to order PCBs. If I need to do more of these, I think I'll use proper PCBs.

BUT! I might reconsider the 230V side.
As the LEDs are here to show if fuse (primary side) or thermistor (secondary) are busted/triggered, I might put both on the secondary side (If I really needed indicator on the 230V side, I think I'd use a neon lamp to keep things simple and safe).
As for the bridge rectifier, I now consider replacing it by a single diode: most of the time the LEDs will be hidden, therefor flickering is not an issue.
Summary: Both LEDs on the secondary, single diode, flickering not an issue.

[Zero999]

How about using a bipolar LED, which consists of two LEDs connected back-to-back?
https://www.tme.eu/Document/386b8c4a49556bd24d89add1cb5b58cf/OSWW428131A.pdf

[Seekonk]

This thread sounds like a punch line for.... How many people does it take to light a bulb?

That compels me to add one more solution.   55V AC not enough for a neon! Put an inductor and capacitor in series.  Tune to near resonance.  Put neon across inductor with limiting resistor.

I have some beautiful quiet German muffin fans that are 240V.  I just put a capacitor in series with them and they run fine at 120V, creating 200V at the fan.