When the signal VAMP falls below a given level (preselected by the reference voltage signal PWM V REF), the output of comparator 709 shown in FIG. 7 toggles HIGH. This output value is latched by flip-flop 710 (part number 74HC74 available from Texas Instruments and other vendors) which is being clocked at a very high speed (approximately 150-250 kHz from the astable multivibrator, not shown).