Pic12f683, Trisio, High Z, A2d

[keithdoxey]

Does the PIC have a common ground with the circuit you show in your diagram ?

[Acetronics2]

A good question would be How much are Va and Vb ...

probably more than the VDD supply of the pic ...


gave you some idea for debugging your Pic batt charger ???

Alain

[jmbanales21485]

well, i guess i missed that little detail in the schematic. I used the voltage from Vb to power the PIC (VDD) and also used the same common ground for Vss. I'm making a battery charger and basically i want to take the voltage measurement at Vb while there is no current going into the battery from the outside voltage source Va (i want to do this because the voltage of the battery increases while the current is going into the battery, however when the current is removed i can measure the voltage of the battery and it will be closer to the open voltage.)

I hope this makes a little more sense.

[jmbanales21485]

Vb = 4v
Va = 9v
Ic = 280 mA (while in LOW state)
Ic = 0.05 mA (while in High Z state)

if this helps at all

[keithdoxey]

You need to use an NPN transistor to drive R3 not the PIC.

Because the PIC is powered from 4V the voltage on its pins cannot exceed 4.6v due to internal protection diodes. This means that even when in its hi-z state current will still be flowing via R3 which would explain why you stil have current flowing even when it is supposed to be off.

[T.Jackson]

Keith is 100% correct. The base of Q2 would need to be at the same level as Va in order for it to switch off. 0.6v or more below Va would mean that it's biased on.
You will find that in its current form Q2 is actually always on.

Trent Jackson

[jmbanales21485]

I'll try that solution as soon as i can and get back to you to see if it worked out. but everything seems logical thanks.
jose

[jmbanales21485]

The NPN Transistor driving R3 works fine. thank you all for your help it is greatly appreciated!

jose