e105d41b_Circuit_Based_on_the_555_Timer__PURPOSE
[PIN] 3 [DESCRIPTION] Output [PURPOSE] 
The output pin is used to drive external circuitry. It has a "totem pole" configuration, which means that it can source or sink current. The HIGH output is usually about 1.7 volts lower than +V when sourcing current. The output pin can sink up to 200mA of current. The output pin is driven HIGH when the trigger pin is taken LOW. The output pin is driven LOW when the threshold pin is taken HIGH, or the reset pin is taken LOW.
DPRG: A Simple PWM Circuit Based on the 555 Timer
PURPOSE