PulseWidthModulation(PWM)LEDDimmerCircuit.pdfVIP

Pulse Width Modulation (PWM) LED Dimmer Circuit Using a 555 Timer Chip Goals of Experiment ? Demonstrate the operation of a simple PWM circuit that can be used to adjust the intensity of a green LED by varying the value of one resistor. ? Demonstrate how a square wave generator can be built using an operational amplifier. ? Demonstrate how a summing amplifier can be used to add a dc offset to a time-varying signal. ? Describe how to test complex circuits. Pulse Width Modulation An energy efficient technique that is used widely in industrial and consumer electronics to vary the power dissipated by a load. – Electric motors – Electric stove elements – Light dimmers PWM Circuit with 555 Timer How a 555 Timer Works ? Astable Multivibrator Mode /480_555.htm /480_555.htm Voltage Comparator ? Op Amp circuit without a feedback component. –Output voltage changes to force the negative input voltage to equal the positive input voltage. ? Maximum value of the output voltage, V , is V+ if the o negative input voltage, v , is less than the positive input 1 voltage, v . 2 ? Minimum value of the output voltage, V , is V- if the o negative input voltage, v , is greater than the positive 1 input voltage, v . 2 /480_555.htm Transistor ? As you will learn in ECE 2204, a transistor can be designed to act like a switch. –When a positive voltage is applied to the base of the transistor (B), the transistor acts like there is a very small resistor is bet