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Transformerless power supplies circuit, cheatsheet and questions

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not1xor1:

--- Quote from: waste on February 06, 2019, 06:39:07 pm ---
--- Quote from: not1xor1 on February 06, 2019, 01:19:48 pm ---The datasheet specifies the maximum working voltage.
With higher voltage there is loss of insulation so you risk to burn all your leds.
Probably that is affected by environmental conditions (temperature/pressure/humidity) too.


--- End quote ---

So using a 1/2watt or a 1watt resistor makes sense as it can take more abuse from higher voltages, the issue can be with the 1/4 1MΩ resistor that discharges the capacitor. Did I get it correctly?

--- End quote ---

that was just an example...
other manufacturers may produce resistors able to withstand higher or lower voltages
anyway in most cases a 1W resistor might work

mariush:
As long as we're at the subject of non-isolated power supplies it's worth mentioning that there are also linear regulators that can work with up to 440v input voltage.

For example LR8K4 can output up to 20mA, provided you don't exceed the power dissipation: https://uk.farnell.com/microchip/lr8k4-g/linear-volt-reg-0-02a-440v-to/dp/2448524

So for example, let's say for a micro that uses only 1-2mA, you could simply have a diode for half wave rectification and let's say a 1uF capacitor, or the minimum to keep the input voltage above around 17v (the regulator needs 12v above output voltage for regulation)

mikeselectricstuff:

--- Quote from: mariush on February 07, 2019, 11:43:23 am ---As long as we're at the subject of non-isolated power supplies it's worth mentioning that there are also linear regulators that can work with up to 440v input voltage.

For example LR8K4 can output up to 20mA, provided you don't exceed the power dissipation: https://uk.farnell.com/microchip/lr8k4-g/linear-volt-reg-0-02a-440v-to/dp/2448524

So for example, let's say for a micro that uses only 1-2mA, you could simply have a diode for half wave rectification and let's say a 1uF capacitor, or the minimum to keep the input voltage above around 17v (the regulator needs 12v above output voltage for regulation)

--- End quote ---
Not sure I can see much benefit of a HV regulator over a simple zener.

Gyro:

--- Quote from: Benta on February 06, 2019, 03:00:34 pm ---"Can you elaborate in what way the wirewound is more robust? It attenuates the surge better for the rest of the elements, or it just more robust for itself."

They are much more robust when it comes to surge overloads.
Think about it: if the circuit is switched on at max. AC voltage (~320 V), we're talking about almost 1 A in 330 ohms, as all caps are discharged.
This works out as a peak power surge (very short, admittedly) of ~300 W. A wirewound will withstand this, a film resistor will not in the long run.
If the resistor is 680 ohms, we're still talking ~150 W.

--- End quote ---

I would go the other way and use an appropriately rated fusible resistor. This sort of circuit tends to be difficult to fuse due to the low current - you don't want a very hot resistor for any significant time. Decent commercial circuits use flameproof fusible resistors to prevent the fire risk.

waste:

--- Quote from: StillTrying on February 06, 2019, 07:22:37 pm ---I doubt applying some 320V square waves is a very accurate way to simulate a bouncing or arcing switch, but I've simulated it that way anyway, :) using the values as in the 1st post.
Green and Grey is with the 33u smoothing cap disconnected, Purple and Yellow is with it connected.
At least in this simulation a way to protect the LEDs from switch-on current spikes Yellow, is to double the 33u value to 68u Blue. YMMV.

--- End quote ---

thanks for the graphs, so bigger capacitors with higher voltage rating are actually quite helpful. I'm actually building a small isolation transformer using 2 transformers back2back so I can test the circuit live and measure the transient volts (not the amperage though my clamp meter doesn't have a max function).

how did you simulate the spikes? Do I get it correctly that square wave is kind of a worse scenario than sine wave? (Ive read that somewhere about generators)



--- Quote from: not1xor1 on February 07, 2019, 06:39:37 am ---So using a 1/2watt or a 1watt resistor makes sense as it can take more abuse from higher voltages, the issue can be with the 1/4 1MΩ resistor that discharges the capacitor. Did I get it correctly?

--- End quote ---

that was just an example...
other manufacturers may produce resistors able to withstand higher or lower voltages
anyway in most cases a 1W resistor might work
[/quote]

The same goes for higher rated resistors :)



--- Quote from: mariush on February 07, 2019, 11:43:23 am ---As long as we're at the subject of non-isolated power supplies it's worth mentioning that there are also linear regulators that can work with up to 440v input voltage.
For example LR8K4 can output up to 20mA, provided you don't exceed the power dissipation: https://uk.farnell.com/microchip/lr8k4-g/linear-volt-reg-0-02a-440v-to/dp/2448524
So for example, let's say for a micro that uses only 1-2mA, you could simply have a diode for half wave rectification and let's say a 1uF capacitor, or the minimum to keep the input voltage above around 17v (the regulator needs 12v above output voltage for regulation)

--- End quote ---
That would be nice for voltage regulated applications (like the micro). Capacitive droppers are current regulated, which is exactly why I find them so sexy for the LEDs.



--- Quote from: mikeselectricstuff on February 07, 2019, 12:08:53 pm ---Not sure I can see much benefit of a HV regulator over a simple zener.

--- End quote ---

Given the fact that LEDs are quite constrained in the Voltage category a zener would have to be very close to their top rating (for the 6 LEDs  example around 19-20Volts), to actually protect them from the surges. Am I interpreting you correctly?



--- Quote from: Gyro on February 07, 2019, 12:32:56 pm ---I would go the other way and use an appropriately rated fusible resistor. This sort of circuit tends to be difficult to fuse due to the low current - you don't want a very hot resistor for any significant time. Decent commercial circuits use flameproof fusible resistors to prevent the fire risk.

--- End quote ---

The flameproofness of my design is in the enclosure. No air and concrete all around the circuit :)
My main concern wasn't the resistor, but also the X2 capacitor which can fail open or closed if I am not mistaken.
using higher rated resistors will make them also run cooler, isn't that true? I usually go for at least double the rating, so instead of 1/4 on the R1 I use 1watt resistors


again thanks for all the input

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