PURPOSE: To ensure the independent setting for the ON- and OFF-time by using the diode to the capacitor charging circuit with a simple constitution of two transistors and thus securing a perfect isolation between the charge current and the discharge current.

CONSTITUTION: With application of DC power source 1, transistors Q1 and Q2 are turned off, and capacitor 3 is charged through resistances R1 and R2 plus diode 2. When the terminal voltage of capactitor 3 reaches the reference voltage, Q2 is turned on quickly with charging of capacitor 3 stopped. The output is at H when both Q1 and Q2 are off, and turns to L with Q2 turned on. When the terminal voltage of capacitor 3 becomes less than the 2nd reference voltage, Q1 and Q2 are turned off again with the output turned to H.