if the diode 20 is placed in parallel with the resistor 18 as illustrated in fig2 the time constant for charging the capacitor 14 becomes r 18 c 14 enabling duty cycles of less than 50 to be implemented therefore by choosing the proper external component values the timer 12 can be forced to oscillate at many different frequencies and duty cycles referring once again to fig1 and 2 pulse position modulation operation of the timer 12 can be illustrated since node va is accessible via a control voltage pin 5 of the timer 12 the voltage at va though normally 2 3 vcc can be varied up or down by applying an external signal to the control voltage pin 5 raising the voltage at va requires that the capacitor 14 charge for a longer period of time before the comparator 56 will change states since it will now have to charge to a higher voltage however if an external signal is applied to pin 5 that lowers the voltage at va the capacitor 14 will not have to charge as long before the comparator 56 will change states as a result of applying a fluctuating signal at va the capacitor 14 charge time will also vary due to the varying charge times of capacitor 14 the output pulse at pin 3 of the timer 12 will vary.