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LT1715 Rail-to-Rail 1MHz Pulse Width Modulator

Rail-to-Rail 1MHz Pulse Width Modulator

In applications where a high frequency variable PWM generator is needed, the LT1715 provides a small and simple solution, as shown in the circuit of Figure 10. The top comparator, U1A, acts as a ramp generator. Biasing resistors R1 and R2 and a 7:1 positive feedback ratio through R3 set the positive input to approximately 2.5V±250mV. The inverting RC feedback creates a relaxation oscillator by tripping the comparator into the opposing output state each time it passes through the ±250mV positive input voltage. The 880kHz triangle wave created on C1 is then passed to the inverting input of the second comparator, U1B. The input signal to be modulated, referenced from 0V to 5V,is first divided to match the 2.5V ±250mV ramp input, and then the duty cycle is set with the second comparator acting as a threshold detector.




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