NTE1753

NTE1753 Integrated Circuit Pulse Width Modulator (PWM) Control Circuit Description: The NTE1753 is a fixed–frequency pulse width modulation control circuit in a 14–Lead DIP type package incorporating the primary building blocks required for the control of a switching power supply. An internal–linear sawtooth oscillator frequency is determined by: 1.1 fOSC ^ RT D CT Output pulse width modulation is accomplished by comparison of the positive sawtooth waveform across capacitor CT to either of two control signals. The output is enabled only during that portion of time when the sawtooth voltage is greater than the control signals. Therefore, an increase in control–signal amplitude causes a corresponding linear decrease of output pulse width. The control signals are external inputs that can be fed into the dead–time control, the error amplifier inputs, or the feed–back input. The dead–time control comparator has an effective 120mV input offset which limits the minimum output dead time to approximately the first 4% of the sawtooth–cycle time. This would result in a maximum duty cycle of 96%. Additional dead time may be imposed on the output by setting the dead time–control input to a fixed voltage, ranging between 0 to 3.3V. The pulse width modulator comparator provides a means for the error amplifiers to adjust the output pulse width from the maximum percent on–time, established by the dead time control input, down to zero, as the voltage at the feedback pin varies from 0.5 to 3.5V...