The current is limited to about 5 milliamps ... For proper operation, the input must be a square wave with 50 percent duty cycle. A pulse with something other than a 50 percent duty cycle can be used ...

increasing Q2’s collector current and C2 ramp rate, thereby making the timeout shorter. If it’s >50%, A2 will ramp down, decreasing IcQ2 and lengthing the timeout. Net result: after a few seconds, ...