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masterx81
Joined: 05 Apr 2002
Posts: 26
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 24 Jul 2004 9:08 Duty cycle to voltage... |
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Hi to all...
I'm a beginner and I need a simple circuit that convert a signal of 150hz with variable duty cycle (from 0 to 100%) to a constant voltage proportional to the duty cycle...
I have tryed to find in internet, and I think that I need a lc filter (i am not sure...) , but I not say how calculate the values of the components...
Thanks to all!!!
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hill
Joined: 17 Jun 2004
Posts: 285
Helped: 9
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| 24 Jul 2004 9:12 Duty cycle to voltage... |
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| Use a R and C combination. R in serial, C in parallel with your load. I think this is the simplest form.
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masterx81
Joined: 05 Apr 2002
Posts: 26
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| 24 Jul 2004 9:18 Re: Duty cycle to voltage... |
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| hill wrote: |
| Use a R and C combination. R in serial, C in parallel with your load. I think this is the simplest form. |
ok...
mmm... How i can calculate the exact value of the resistor and capacitor?
After the rc I think that i need also a transistor (because the load do not discharge the capacitor before the time), right?
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batdin
Joined: 03 Jun 2004
Posts: 181
Helped: 3
Location: Bulgaria
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| 24 Jul 2004 16:12 Re: Duty cycle to voltage... |
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It depends on your load resistance.
Depends also on the output ripple than can be tolerated.
What is the signal source?Can it supply enough current to the load or should it be amplified beforehand?
Give some details.
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Einstein
Joined: 19 Dec 2003
Posts: 1
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| 24 Jul 2004 17:09 Re: Duty cycle to voltage... |
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| This sounds like a what is used in a chopper. Can you be more specific about the input waveform? If you look on the net for "chopper circuit" you'll find some stuff!
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masterx81
Joined: 05 Apr 2002
Posts: 26
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| 24 Jul 2004 17:22 Re: Duty cycle to voltage... |
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the input signal is an inverted square wave (normal +12) with a variable duty cycle. The output need to be a variable voltage (form 0 to +5, 0 when the input is @ +12 -0% duty-) depending on the input duty...
I'm considering to use an operational amplifier...
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dumbfrog
Joined: 17 Jul 2004
Posts: 191
Helped: 4
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| 24 Jul 2004 19:33 Re: Duty cycle to voltage... |
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| yes, use an opamp integrator
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masterx81
Joined: 05 Apr 2002
Posts: 26
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| 24 Jul 2004 20:02 Re: Duty cycle to voltage... |
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Another little qustion...
Sorry for the banality of the domand but...
The opamp insert a little tension to the output(ca 2.5v), how i can remove it???
I'm using a tl074cn (quad opamp) with single supply (+12)
Thanks for the help!!!
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eternal_nan
Joined: 10 Mar 2003
Posts: 158
Helped: 15
Location: eternity
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| 24 Jul 2004 20:51 Duty cycle to voltage... |
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| Assuming you already have a DC voltage available to power your circuit, what you are looking for is called a DC-DC converter, they come in several varieties: buck, boost, buck-boost, flyback and other topologies that are mainly derived out of the above 4. There is lots of info about these circuits on the web, search in google.
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mazelk
Joined: 23 Apr 2004
Posts: 107
Helped: 2
Location: COLOMBIA
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| 25 Jul 2004 7:09 Re: Duty cycle to voltage... |
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Hi...
Assuming that the amplitude of input square signal is 12 V, you may get first an inversor. If the output sholud be 0 when input signal is 12 V, 0% duty, this may significates that in this moment, input signal is 12 VDC. This improve allows output DC signal increases when pulse width increases.
After this, you can converts the input-inverted-square signal, in a triangle signal, applying, for example, a Miller integrator. Based in triangle amplitude (that is proportional to pulse width), you may get the DC signal with, for example, simple diode-RC schematic; keeping low output ripple.
Typically, this solution should be non-linear.
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masterx81
Joined: 05 Apr 2002
Posts: 26
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| 26 Jul 2004 8:04 Re: Duty cycle to voltage... |
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Ok, I have find all the information but...
The opamp that I have, also in configuration voltage follower, when are at state low, they are @ ca 2,5volt (not 0...).
I'm using it with +Vcc->12v and -Vcc->Ground...
Whot I am doing wrong???
I need opamps designed for single power supply?
Thanks!
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