Technician Handbook ! 673 Electronic & Computer Controlled Systems Duty Cycle When voltage alternates repeatedly between a high and a low value, the ratio of time the voltage is high compared to the time it is low can be used to control components. The ratio is called the duty cycle . An example is in controlling the brightness of the dashboard illumination. Older vehicles used a variable resistor to increase or decrease voltage to the lamp to make it brighter or dimmer. In electronic circuits, a modulator can turn a circuit on and off hundreds of times per second.
If the amount of time the circuit is ON equals the amount of time the circuit is OFF, the lamp is receiving 50% of the power it would receive if the circuit were just left ON. When the ON time equals 50% of the complete cycle, it is referred to as a 50% duty cycle. Similarly, when the ON time equals 75% of the complete cycle, it’s a 75% duty cycle. 28 Technical Training