Invert a 555 Astable Output Signal

Posted on Feb 4, 2014

A variable frequency, variably duty cycle 555 configuration in astable mode. I`m using a set of pots to get a wide range of control. It works beautifully. The output is great, but I have a problem. I am driving a couple mosfets directly from the output. But I want to have a third mosfet that turns on and off opposite to the timing of the first two. So if I`m running 25% duty cycle, the first two are ON for 25%

Invert a 555 Astable Output Signal
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of the cycle while the third one is OFF during that portion and then reverse this for the OFF period of the cycle. I`ve seen some diagrams that talk about using one extra mosfet or one extra transistor along with a resistor to invert a signal, but they don`t create hard/fast rise and fall times. The resistor causes slow rise times. I want a nearly perfect inversion of the square signal. Right at the moment that the first two mosfets flip off, the third mosfet needs to flip full on. It`s critical that I get this to be as accurate as is feasible without getting into overly complex circuitry. Anything more than two or three 555s and/or two or three extra transistors (possibly needed to invert the signal) is more than I`m bargaining for. I`m not posting this as an answer yet, because I`m waiting to hear a response from the other answerer. But apaprently you can run a 555 as a 200mA signal inverter. This is really simple for a person who already has 555s on hand, and the best part is that the 200mA current is WAY higher than a typical logic unit inverter (often topping out at least than 10 or 20mA). Here`s a page with a circuit at the bottom explaining Inverter mode:

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