i have a PIC which i want to use in a car to run 2 relays. the relays are 24v, but switch at about 10v, and the pic switches the relays with 2 2n2222 transistors. the transistors are connected to the pins of the pic with 1kohm resistors. the pic will also run one LED.

i want to use a zener diode to get 5v to the PIC, i have made a simple regulator with a diode and a 220ohm resistor, and connected the 5v from the zener to one of the transistors (to simulate the pic pin) and it doesn't seem to have enough current to switch the transistor.

 

beware that the relays may not be reliable used in this way.
a three termial regulator is so cheap why not use it?
But the zener regulator should work if done correctly.
I have not looked up the 2n2222 but it seems off hand that it
should work ( adding a bit of voltage drop which may explain why the relay does not work ).

 

kay well i got it to work, seems that if you leave out a ground connection the relays won't switch hehehe. i had a regulator on there (1.5A) but it was big and i ran out of space on my veroboard (bad planning). maybe i will go for a smaller one though.

it seems each transistor draws about 8 ma when on, and worst case senario will have 3 relays on + PIC + LED. the 1/2w resistor already gets warm if i push the input voltage up to around 15v and have 1 relay on ;-(

 

i had a regulator on there (1.5A) but it was big and i ran out of space on my veroboard (bad planning). maybe i will go for a smaller one though.

A TO-92 78L05 is good for 100mA and is similar to the size of a 2N2222.

 

7805 voltage regulator. use that.

sites/fasttimesatnau/?&nats=MTAyODo0Ojk

 

yip i guess regulator will work way better than zener diode. thanks ;-)