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Thanks for the information. So based on your description does the following
attachment look correct? I modified one of your diagrams off your site.

Does it matter what freq. I use for the PWM?

I am looking at having a total of 4 channels. Should I just replicate the
circuit 4 times or is there other possibilities.

In addition, each channel will have its own + 8v supply input. I could use
the first channel to drive all of the outputs and power the PIC. I could
also use channel 1 to power the PIC and its output and the rest of the
channels power just their outputs. Which do you think would be better? Would
it be to hard to "tune" each of the channels from separate power sources
versus just using one power source?


thanks again,
Frank

----- Original Message -----
From: "Roman Black" <fastvid@EZY.NET.AU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, February 02, 2003 6:52 AM
Subject: Re: [PIC] PWM signal to 4v min - 7.5v max output


> See my 2-transistor Black regulator here;
> http://www.romanblack.com/smps.htm
> (especially see smps_cir.gif)
>
> This 2 transistor setup can be modified to work
> your circuit with PWM;
> * remove zener, RZ, C1 and C2
> * connect emitter of Q2 to gnd, NOT the output
> * use a 3k3 resistor between PIC pin and Q2 base
>
> Obviously the PIC swithes the thing on/off for the
> right PWM times to adjust the output voltage.
>
> You can use anyhting from about 220uH to 2200uH for
> the inductor, as long as it takes your max current
> without getting too hot.
>
> All other parts values are ideal and cheap and should
> work well with your 8v 0.5A supply. The BC327 has a
> nice low Vce on voltage and you will only lose about
> 0.2v from C-E when on, meaning you can get up to
> 7.8v out from your 8v supply.
> -Roman
>
>
> Frank J. Soria wrote:
> >
> > Anyone?
> >
> > Frank
> > ----- Original Message -----
>
> > I am sure this is very very simple circuit. I need to convert a PWM
signal
> > from a PIC to create a +4v to +7.5V DC control voltage. I am limited to
a 8v
> > 0.5a max power supply. I have been reading that i need a low pass filter
and
> > an op amp. But I really need specific parts and a circuit digram. And
basic
> > description on how it all works would help greatly.
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics
>

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+8v---------------------*--------,
                        |        |  Q1
               470 ohm  R1       |  PNP
                        |        E  BC327
                        *------B
                        |        C
                        |        |          (measured:)
                   2k7  R2       |   2.2mH  (1960uH, 2.4 dc ohms)
                        |        |
             NPN BC337  |        *----L1----*--- ~ 0 to +7.8v out
                        C  Q2    |          |
PIC PIN-----R3--------B          |          |
           3K3          E        |          |
                        |        |          |
                        |        |          |
                        |        |          |
                        |        |          | 47uF
                        |        |          C 16v
                        |        ^ D1  1A   |
                        |        | schottky |
                        |        | 1N5819   |
                        |        |          |
Gnd --------------------*--------*----------*------ Gnd

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