Author Topic: PIC 12F683 low PWM output voltage  (Read 3257 times)

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Offline lkTopic starter

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PIC 12F683 low PWM output voltage
« on: May 14, 2012, 08:45:40 am »
Greetings,

i have noticed something odd with the output voltage on my PIC 12F683, the CCP1 module outputs around a signal that is around 0.9 Vpp, and this strikes me as odd, i have a scope on it, the duty cycle changes as i would expect. Maybe I'm naive, but i would have expected a 5Vpp signal coming from the 12f683. 

The only thing i can think of that is that it has something to do with this maybe

110x = PWM mode active-high
111x = PWM mode active-low

But I'm not clear on what this mean, but i suspect that it has something to do with the duty cycle is counted on high or low, but I'm not sure.

So if anyone could enlighten me it would be great, I'm sure its something simple :)
 

Offline lkTopic starter

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Re: PIC 12F683 low PWM output voltage
« Reply #1 on: May 14, 2012, 02:51:11 pm »
Opps, looks like the pic is indeed putting out 5volts, there was a problem in my circuitry :)

Looks like i get a voltage drop of around 4 when i connect to a base/gate for a transistor. "floating" i have 5 volts on the pin, and the pwm signal looks perfect.


-lk
« Last Edit: May 14, 2012, 03:12:39 pm by lk »
 

Offline metalphreak

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Re: PIC 12F683 low PWM output voltage
« Reply #2 on: May 14, 2012, 05:26:09 pm »
You should be using a current limiting resistor between the PIC output pin and the transistor base. From what I remember you can only source about 20mA max from each micro pin.


There should be ~0.7v drop across the transistor base-emitter juntion. If the emitter is connected to ground with the load on the high side, then the rest of the voltage will be dropped across the base resistor. If your measuring point was on the base pin, you'll only have been measuring that base-emitter voltage, not the output from the PIC :)
« Last Edit: May 14, 2012, 05:28:19 pm by metalphreak »
 

Offline lkTopic starter

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Re: PIC 12F683 low PWM output voltage
« Reply #3 on: May 14, 2012, 05:48:55 pm »
Thanks,

i have it solved, turned out to be a faulty fan, combined with my inability to read the display on my psu :)

-lasse
 


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