PWM variable frequency to Analog Voltage

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ValGurdis

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Hi.
I need to convert a PWM signal with variable frequency and 50% duty cycle, to Analog Voltage. How can I do it? Are there any ICs for this?
Thanks
 

Solution
Are you asking for a frequency to voltage converter or a PWM to voltage converter?
PWM implies the pulse width can vary so perhaps what you are referring to is a square wave.
Techniques for F to V and PWM to V conversion are quite different.

Brian.
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Are you asking for a frequency to voltage converter or a PWM to voltage converter?
PWM implies the pulse width can vary so perhaps what you are referring to is a square wave.
Techniques for F to V and PWM to V conversion are quite different.

Brian.
 

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Solution
Hi Brian,

thanks for response.
You are right, it is a square wave.
Basically I have a fan to control that has a tacho output which is a square wave and the frequency of it is proportional to the speed of the fan.
I need to read this output as an analog voltage as all I have available for this is an analog input on my controller.
The frequency of the tacho signal goes up to 700 or 800Hz.

thanks
 

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Besides using a dedicated f/V converter IC, you can use a monoflop or an equivalent circuit that generates a pulse of constant width for a tacho pulse and filter the pulses to a DC voltage.
 

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You can also do this with an asymmetrical RC filter, if you differentiate the square wave first,

i.e. put it thru a series RC ( or just C ) with an R to gnd, this gives a spike for every edge, then:

through a fast signal diode and an R to charge up a cap, C2, and a larger R across the cap, C2 to more slowly discharge C2, you can then post filter this with a smaller RC filter if you wish - not always necessary,

as the freq goes up the impulses per second to the filter go up giving a higher ave o/p voltage.
 

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Hi,

thanks to all for your answers.
I think f to V IC will be the solution.
As I have two fans to control, are there any dual channels f/V IC?
Any particular suggestions?
 

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Hi,

You may do an internet search, or do a search at electronics distributors (this is what I'd do).

Depending on how you want to measure and process the information ... maybe you may use a single f/V converter with a MUX at the input.

Klaus
 

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