PWM signal for switch is generated by comparing sawtooth waveform generated by NE555 with error amplifier signal. Duty cycle is reduced to keep inductor current at maximum level set by current sense resistor. If current comparator detects peak current it turns off transistor switch. This is done by logic shown on schematic. Transistor is enabled again in next clock cycle because CS comparator latch is reset by low signal on PWM generator output. This circuit is also short circuit resistant.
