PNP invert 555 output?

[justDIY]

I would like to invert the output of a 555, so that I can use two N-channel mosfets (Q1 and Q2) to switch my loads, opposed to one N and one P channel. I thought I could accomplish this using a PNP transistor (Q3) to feed one of the fets 12v, while the output of the 555 is low, but it doesn't seem to work this way.

I have the circuit built in the diagram, however, the base of my transistor is constantly at 12v, even when the output "Q" is low from the 555. Connecting the base resistor directly to ground switches the transistor (and connected mosfet) as expected.

From what I read in the datasheet, the LM555C (cmos version) can source and sink 200mA ... so I would have thought, when the 555 goes low, sinking current, it would also pull the base of the transistor low. Although not pictured in the diagram, the 555 is also powered by the same 12v rail as the transistors.

I have tried different resistors for the base, with no effect. Any ideas on what I've missed?

thanks!

 

[justDIY]

i removed R3 and all is now well

 

[audioguru]

Look at the Cmos LMC555's datasheet. Its output can sink to ground only 50mA and it can source high only 10mA. With these currents the output voltage is no where near ground or the positive supply.