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walters
Joined: 05 Jun 2005
Posts: 496
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 12 May 2008 5:19 Square waveform needs duty cycle adjustsment |
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My function generator Square waveform output does not have a duty cycle adjustsment parameter
What kind of circuit/network can i hook up to it so i can adjust the 50% squarewaveform to any duty cycle % percentage from 0% to 99%??
What circuit can do this please?
My Triangle output does NOT have a "Symmetery" parameter how can i hook up a Function generator output triangle waveform and what circuit/network will adjust the positive and negative symmetery?
My Function generator does NOT have DC offset adjustsment parameter , What can i hook up to it so it can have a DC offset adjustsable?
I was thinking i can hook up a 9 volt battery with a 1Meg pot to variable the DC 9 volts from zero 0volts to 9 volts and put that on the function generator RED probe
Would this create a DC offset network for the function generator?
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kiprono
Joined: 18 Nov 2005
Posts: 244
Helped: 15
Location: Nairobi
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| 14 May 2008 20:09 Re: Square waveform needs duty cycle adjustsment |
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| Use this PWM IC: SG3525A. It is low cost and meets your requirements.
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VVV
Joined: 26 Nov 2004
Posts: 1403
Helped: 256
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| 15 May 2008 18:37 Re: Square waveform needs duty cycle adjustsment |
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If your function generator does not have these features, then there is little you can do externally. Basicaly, the symmetry/ duty-cycle are both adjusted the same way: by distorting the triangle output, which is later used to create the swuare wave and sinewave. So the adjustment should be there.
If it isn't, then you cannot add it.
For square wave you can add exteranlly a one-shot and adjust its duration. That way you get variable duty-cycle. But the duty-cycle will change with changing frequency.
For DC offset, you can use an external opamp summing amplifier and feed to it both the waveform from the generator and an additonal adjustable DC voltage, which will control the offset. The solution you mentioned will not work because the generator has a low output impedance, which will basically short to ground the DC voltage you are attempting to add.
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Miguel Gaspar
Joined: 06 Mar 2006
Posts: 386
Helped: 36
Location: Culiacán, Sinaloa, Mexico
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| 15 May 2008 20:00 Square waveform needs duty cycle adjustsment |
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You can use the XR2207, you can find the datasheet in:
www.exar.com
it is an excelent chip, but the maximum frequency is 1MHz
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v_c
Joined: 11 Oct 2005
Posts: 465
Helped: 84
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| 15 May 2008 21:17 Re: Square waveform needs duty cycle adjustsment |
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If your function generator can produce a sawtooth or a triangle wave, then you can use this with a comparator to produce the duty cycle that you want. You basically have to feed the triangle or sawtooth to one of the comparator inputs and feed the other comparator input with a dc voltage that varies from the sawtooth or triangle maximum to minimum. As you vary the dc voltage from max to min your duty cycle at the output of the comparator will vary from 0 to 100%.
Best regards,
v_c
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walters
Joined: 05 Jun 2005
Posts: 496
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| 16 May 2008 6:55 Re: Square waveform needs duty cycle adjustsment |
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For DC offset, you can use an external opamp summing amplifier and feed to it both the waveform from the generator and an additonal adjustable DC voltage, which will control the offset. The solution you mentioned will not work because the generator has a low output impedance, which will basically short to ground the DC voltage you are attempting to add.
1.) So how can i do it then? how can i add DC offset to my function generators output?
If your function generator can produce a sawtooth or a triangle wave, then you can use this with a comparator to produce the duty cycle that you want. You basically have to feed the triangle or sawtooth to one of the comparator inputs and feed the other comparator input with a dc voltage that varies from the sawtooth or triangle maximum to minimum. As you vary the dc voltage from max to min your duty cycle at the output of the comparator will vary from 0 to 100%.
Since the input is Triangle would it be called Symmetery? not duty cycle?
Whats the difference between Symmetery VS duty cycle?
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