>1.    Produce hardware PWM variable from 0 to 100% at at least 20 kHz.
>
>2.    Input to be an analog voltage SOMEWHERE in the 0 to 5 volt range. eg
>may be 0 - 3 or 2.3 - 4.2 or whatever. Circuit needs to be able to be
>
>3.    Linearity and accuracy not overly crucial but the better the better.
>eg 1% excellent, 5% OK, 10% is rather marginal .
>
>4.    PWM waveform shape is not crucial but the sharper the rise and fall
>edges the better.
>
>5    Sensitivity to component values included in 3.

>6.    Assessment of all up cost is informal. eg includes components, board
>area and assembly costs but no formula is proposed for these. Construction
>would probably be single sided with links as requisite. Machine assembly
>with manual backup as required. Assembled in PRC - labour is cheap!
>
>7.    Target volumes are low to moderate production - say 100s to 10,000
>range but one off amateur applications may benefit from this.
>
>8    Frequency of PWM is not too critical. eg 22 to 28 kHz would be OK for
a
>nominal 25 kHz design. .

Check out the Intersil HIP408x series. We used the HIP4080 in a space cooler
drive application at 75Khz (it was going to be higher, but suitable rad-hard
FETs were not available to us), but if you need to get down to 25kHz then
that should be do-able. See
http://www.intersil.com/product_tree/product_tree.asp?x=15 and expand out
the trees to find the devices. They are available in DIP and SM versions.




>Dedicated PWM ICs would be fine if the price was OK. An LM324 is VERY
cheap.

This may be where the HIP408x will fall down. IIRC Jinx looked at them a
while back, and moaned about the 1 off price through RS. However the app
notes will help you with some of the other points above.

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