Transformerless / transformer Power Supply Design?

I am solving how to power the electronics that must GND at the potential of L network. I need 25mA +3,3V and GND on L1. Device is powered permanently 7/24.

The first option is Transformerless Power Supply with C.
The second option is small trasnsformer
The third option is DC/DC converter from low side. There is a problem, the secondary side does not necessarily need to work 7/24

Because GND must be on L1 potencial I thing can only be used this type of transformerless PS

because half wave is always destroyed on Zener will be effective indicatively 20-25%.
My question.
Is there any way to increase efficiency for transformerless PC where is GND on L1?

Transformer design,use any asi BV2010123
What is the real effectiveness of these small transformers?

By "must GND at the potential of L network" do you mean your load ground side (but not Earth) must be connected to one of the AC lines directly?
What do you mean by "L1"?

Brian.

Is there any way to increase efficiency for transformerless

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This 'power supply' topology should be considered only as a secondary option due to the obvious reason of being unsafe from the point of view of the handling, but a very relevant aspect is its intrinsic inefficiency, manifested in the form of (much) dissipated heat, the lower the load being consumed, the greater the heating; ie if the powered system is in an idle state, the series resistor on this 'power supply' will have its highest dissipation.

What frequency and voltage is your AC source?

I'm sorry this information fell out of my text.
My app is something like power meter o power network analyzer. Power is 230V 50Hz

>Why must GND at the potential of L network
because first ADC measure current on 500uOhm - 1mOhm shunt resistor and one of the end of the resistor must be on the ground potential of the ADC.
Second ADC measure voltage between L a N and use resistor divider 1M/1k on Neutral line.

please show L network and shunt resistor with the power converter
it is much easier to help when everything is known

230V @50 Hz to 3.3V @ 25 mA

i think you're much better off with a transformer from the website you included in the first post
rectify the secondary, put capacitor on it and then regulate however you like
give yourself 2 V overhead - that is, the output of the transformer secondary should be >= 2V above your desired regulated voltage at low input line voltage

That is a question, maybe yes may be not.
The key question is the efficiency of a small transformer 0,35 or 0,5VA .
My guess is, it will be one big tragedy, but I am wrong, there is some real measurement of the efficiency of transformers under 1VA?

I think the solution depends on how the power monitor reports what it measures. Small transformers are not particularly inefficient and they do offer the advantage of isolation. If you are making any electrical connection outside of the circuit, other than by a wireless method, you must have isolation to prevent unwanted current paths and their inherent dangers. If circuit is entirely self contained and insulated from contact, you can use the capacitive dropper method but add a resistor across the capacitor to discharge it if the power is removed. Keep the series resistor fairly small (use a safety rated type) and keep the capacitor value as small as possible while allowing enough current flow to the load. In other words, maximize the drop in the capacitor where dissipation is lowest.

Consider that you can still measure current and voltage on the 'live' side of a circuit while running on the isolated side if you use differential methods and high enough series resistances that the leakage current is at safe levels.

Brian.

because half wave is always destroyed on Zener will be effective indicatively 20-25%.

Click to expand...

No. As long the output voltage isn't exceeding the zener voltage, there's no power burnt in the zener diode (except for rectifier voltage drop). Thus the efficiency can be considerably higher than 25%. Design for wider input voltage range and output current margin can however involve low efficiency.

As for the miniature transformers, there's a "no load power loss" specification with each transformer type which is obviously dominating losses. For lowest losses, you'll go for the new Erp series.

For example 0,35VA HAHN page 22 noload power loss type 1,2W for 0,5VA noload power loss type 1,5W , if we neet 6V 20mA 0,125W => big tragedy :-D

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Another power supply option, using a non-isolated converter for example **broken link removed** , but effecincy is about 40%