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Design for voltage measurement

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Gomez

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site:www.edaboard.com ac voltage measurement

I need a design for voltage measurement.

- primary side
- 170V - 260V
- U -> PWM (optocoupler)
- no transformer
- simple design
- accuracy 5%

Best Regards

Gomez
 

TomAss

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ac voltage measurement without transformer

Hi,
look at this application note by National Semiconductors

www.nsc.com

It decribes an ultra-high isolation amplifier powered by
an ultrasound transducer (!).
The input side voltage is converted to frequency then
opto coupled to a frequency to voltage converter.
Instead of using such a transformer for input side power supply,
you can get it directly from the input AC line with a trasformerless
power supply built with a capacitor, a resistor and a zener diode.
Remeber that in this way you have the maximum circuit simplicity, but
the input side will be exposed to every transient on the AC line, so
you should use all precautions (dischargers & co) to prevent circuit
damages due to spikes and transients.
Remeber also that the input side will be at dangerous potential, so
the opto coupler and the PCB should met your safety standards according
isolation.

i think that with some simple modifications this circuit
will be right for you.

Bye
 

flatulent

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One scheme

One way to power the primary side without transformers is to use a resistive voltage divider on the power line side to get a low AC voltage that you rectify and filter to power your circuit. Arrange the divider so that your circuit is on the end of the divider that is at ground or neutral voltage.

As stated above, safety is a real issue. Your circuit should be in an insulated box and only the wires from the optoisolator output side should come out to the outside, low voltage world.
 

tjalps

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Check this! It's wery good!

hxxp://www.analog.com/Analog_Root/productPage/productHome/0%2C2121%2CAD215%2C00.html
 

Gomez

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Re: One scheme

flatulent said:
One way to power the primary side without transformers is to use a resistive voltage divider on the power line side to get a low AC voltage that you rectify and filter to power your circuit. Arrange the divider so that your circuit is on the end of the divider that is at ground or neutral voltage.

As stated above, safety is a real issue. Your circuit should be in an insulated box and only the wires from the optoisolator output side should come out to the outside, low voltage world.
My circuit is only a small part. The optoisolator is UL listed. I need a simple circuit with standard elements (V/f-converter), no special ICs. Is for production. The problem is the transients and spikes and precision. UL will test the device.

Gomez
 

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