# Calculating output voltage

#### Weras Asdsdw

Joined Feb 14, 2016
7
Can someone tell me what is output voltage for this scheme?

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#### dl324

Joined Mar 30, 2015
11,317
Welcome to AAC!

Is this homework? Is the voltage AC?

#### Weras Asdsdw

Joined Feb 14, 2016
7
Yeah the voltage is AC

#### dl324

Joined Mar 30, 2015
11,317
Is this homework?

#### Weras Asdsdw

Joined Feb 14, 2016
7
Kind of...

#### dl324

Joined Mar 30, 2015
11,317
What do you think the output will be?

Are you actually building this circuit?

#### AnalogKid

Joined Aug 1, 2013
8,542
The output is a half-wave rectified sinewave. Beyond that, your question needs a lot more work.

If you are asking what the output voltage will be if measured with a digital voltmeter, it depends entirely on the load. It has a peak value, an average value, an RMS value, and an incorrect DC value on a meter - and all four of these are different numbers. If the load is a resistor, then the 1 M resistor in your drawing is one part of a voltage divider. If the load is a capacitor, then the size determines what will appear on a meter.

ak

#### Weras Asdsdw

Joined Feb 14, 2016
7
No this is part of bigger scheme, I think it should be around 5V

#### dl324

Joined Mar 30, 2015
11,317
No this is part of bigger scheme, I think it should be around 5V
What is the voltage drop of a diode? What will it do on the negative half cycle of the input?

#### Weras Asdsdw

Joined Feb 14, 2016
7
The output voltage should activate the optocoupler
The measured voltage output was 0.5V but the optocoupler didn't activate, so I think it should be around 5V for it to work

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#### dl324

Joined Mar 30, 2015
11,317
The output voltage should activate the optocoupler
How are you coming up with 5V for the output?

You said this was "sort of" homework. Is it or isn't it?

#### Weras Asdsdw

Joined Feb 14, 2016
7
Its not homework

#### dl324

Joined Mar 30, 2015
11,317
Its not homework
Then as AK said, the output will be a half wave rectified sinewave and the voltage won't be 5V (DC or AC). You need to add reverse polarity protection for the opto LED.

#### Weras Asdsdw

Joined Feb 14, 2016
7

#### dl324

Joined Mar 30, 2015
11,317
You're welcome.

To protect the opto LED, you can install the existing discrete diode anti-parallel to the LED.

#### roger finder

Joined Nov 3, 2015
5
half wave rectifier voltage - diode drop voltage

#### hp1729

Joined Nov 23, 2015
2,304
The output voltage should activate the optocoupler
The measured voltage output was 0.5V but the optocoupler didn't activate, so I think it should be around 5V for it to work
Not enough current to turn on the optocoupler?
Self-assigned homework? If it is assigned homework you will get guidance, not answers.

#### hp1729

Joined Nov 23, 2015
2,304
Can someone tell me what is output voltage for this scheme?
To get the 20 mA or so the optocoupler needs you need about 11,000 ohms, but that would mean you have to be a 10 Watt resistor. The voltage across the LED sets itself. (Maybe 1.2 V?) And yes, use a protection diode.