PIC supply using a DC-DC converter

[CafeLogic]

you are correct it should be an NPN.

It does seem to control speed however quite well, but i will change it to an NPN non-the-less.

Thanks again...

I hope it is not my power supply, but that would be an easy answer and easy fix.

Well, then that right there is the answer to your mystery. If the circuit was correctly wired, the CCP1 PWM line would do absolutely nothing. For the PNP to "turn on" a current must flow from the emitter, which you have grounded, to the base, which is connected to your micro. That should never happen because whether at 0 or 5v the potential of the pwm should always be higher than the emitter. You need to figure out why ground before the DC-DC is at a different potential than ground after. Looking at the datasheet, I see the converter is isolated. If you didnt wire the before and after grounds together that would explain it, hence the solution is just to take a big wire and attach it to the output ground and the other side to the input ground.

As for why it works with the pickit I have no idea. If I were to take a random guess, I would say the ground of the 48V supply is attached to yoru computer ground for some reason, and plugging in the pickit connects the grounds.

 

[Pommie]

Have you gotten this PIC to work off "normal" 5v? To pursue a difficult diagnosis with the SMPS without knowing it's the SMPS is an inefficient way to go about troubleshooting.

From post 5,

when i power it with the pickit 2 there are no issues.

Mike.

 

[deperkin]

I did get the issue with the resetting solved...

It ended up being the 20 ohm resistor for 'brightness'.
I will change all that to an NPN later... for now i removed the PWM wire.

I did add 1k ohm resistors for pulldown... on the buttons... you think these are too small?

Also, i changed the PNP (tip42a) to an NPN (tip41a) and i get the pic to startup with no resets now, but it locks at the first screen. (odd)...

so before i changed anything else i switched it back to a PNP and it works fine again.
This seems odd to me, since it should have been an NPN to start with.

Thanks again. It is now powering very well.

I will post all updates with final pictures and some code after i get this project up and running.

 

[deperkin]

Tachometer

I have been trying to get the tachometer working correctly on this project as well.

An update on the schematic: **broken link removed**

I am using a TIP41A NPN for the speed.

I am checking the voltages with both an oscilloscope and a multimeter.
I am pulling the tach up to 5V.

I get the proper signal from the motor, but am only measuring an average voltage on my interrupt pin of 3.5 V.

on my interrupt routing I am only running a counter. (i.e. ticks++)

I check every second how many ticks I get. It seems to be only showing about 10 ticks per second... I should be getting about 140 per second on this motor.

Can anyone see anything wrong with using the TIP41a in this way ?


thanks as always.