Overview: PJ494 Switchmode Pulse Width Modulation Control Circuit he PJ494 incorporates on a single monolithic chip all the functions required in the construction of a pulsewidth-modulation control circuit. Designed primarily for power supply control, these devices offer the systems engineer the flexibility to tailor the power supply control circuitry to his application. The PJ494 contains an error amplifier, an on-chip adjustable oscillator, a deed-time control parator, pulse-steering control flip-flop, a 5-volt, 5% precision regulator, and outputcontrol circuits. The error amplifier exhibits a mon-mode voltage from –0.3 volts to Vcc –2 volts. The dead-time control parator has a fixed offset that provides T approximately 5% dead time when externally altered. The onchip oscillatory be bypassed by terminating RT (pin 6) to the reference output and providing a sawtooth input to CT (PIN 5), or it may be used to drive the mon circuits in synchronous multiple-rail power supplies. The unmited output transistor provide either mon-emitter or emitterfollower output capability. Each device provides for push-pull or single-ended output operation, which may be selected through the output-control function. The architecture of these devices prohibits the possibility of either output being pulsed twice during push-pull operation.
