# Amplify a sine wave 40-400Hz - 0,6Vpp

Discussion in 'The Projects Forum' started by bading, Dec 29, 2012.

Jan 18, 2012
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I'm designing a sinusoidal generator with voltage and variable frequency (40-400Hz).
I used a AD9833 connected to a PIC18 microcontroller.
The software is ok.
The output of the AD9833 is 0.6 Vpp that I must amplify for 230Vrms.
The generator must have a power of 25VA.
I suggested an amplifier circuit elevator?
Thank's

2. ### Papabravo Expert

Feb 24, 2006
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1,850
What is the purpose of this amplification to 230 VRMS and what power source will you use to achieve this conversion. Have you considered that the output power of any device will ALWAYS be less than the input power? Sometimes it will be a great deal less -- have you considered that?

Jan 18, 2012
10
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The purpose of this generator is to test the electronic protection relays (ANSI81 under e over frequancy) with impedance from 1 to 2 MOhm and consumption from 0.5 to 4VA​​.
I have available a dual DC voltage (±18Vdc).
To increase the output voltage i think of a transformer with 24Vac primary and 230 Vac secondary.
Thank's

4. ### Papabravo Expert

Feb 24, 2006
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1,850
OK so the plan is to generate a signal of 230 VAC from a transformer with 24 VAC on the primary. This source of 230 VAC will be applied to the relay contacts at what current? Answer 0.5 to 4 VA or 2-17 mA

Whatever current that is on the secondary you will need at least 10 times that current on the primary. Let us say the contact specification is 4VA or ≈ 20 mA continuous. You will need at least 24 VAC at 200 mAmps continuous on the primary.

So now you have to get from 0.6 VPP or 0.212 VAC to 24VAC @ 200 mAmps from your dual 18 VDC supply which will be tough. It would be easier with a supply that was plus or minus 28 to 36 Volts. Plus minus 18 would require a boost converter in there somewhere. This is a voltage gain of 41 dB which I would attempt to do in two or three stages. I'm not sure how much current your original source is but probably a couple of mA at most.

Last edited: Dec 29, 2012

Jan 18, 2012
10
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Yes, the source must be connected to the input of 230Vac electronic relay.
The calculations are correct!

6. ### tubeguy Well-Known Member

Nov 3, 2012
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197
With +/- 18vdc I think you could develop 12 VAC RMS so what about a 12VAC:230vac transformer ?

Jan 18, 2012
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Yes, if necessary I could also use a transformer 12Vac/230Vac.
Thank's

8. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Then he will need twice the current on the primary side to get the requisite current out the secondary side.