Processor`s PWM output controls LCD/LED driver

Posted on Apr 19, 2012

The circuit comprises simply the PWM source, capacitor C, and resistors RD and RW. For CMOS circuits, you calculate the open-circuit output voltage as VCONT=D½§VDD, where VCONT is the control circuit`s output voltage, D is the PWM duty cycle, and VDD is the logic-supply voltage. The control circuit`s output impedance is the sum of the resistor values RD and RW: RCONT=RD+RW. For the circuit of Figure 1, the output voltage, VOUT, is a function of the PWM average voltage, The PWM (pulse-width-modulation) output available from many microprocessors is based on an internal 8- or 16-bit counter and features a programmable duty cycle. It is suitable for adjusting the output of an LCD driver (Figure 1), a negative-voltage LCD driver (Figure 2), or a current-controlled LED driver (Figure 3).

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