POWER CONVERTER SOFT START CIRCUIT

摘要

PWM control circuits and soft start circuitry thereof are presented in which a source follower circuit provides an input to a pulse generator error amplifier during startup according to a lower one of an internal soft start circuit ramp signal and a voltage across and externally connected capacitor, with a current source connected to the source follower to limit the charging current supplied to the externally connected capacitor.

主权项

1. A control circuit for providing pulse width modulation (PWM) control of a DC-DC converter, the control circuit comprising:
a pulse generation circuit, comprising:
an error amplifier including a first error amplifier input receiving a soft start input signal, a second error amplifier input receiving a reference voltage signal, a third error amplifier input receiving a feedback signal representing an output condition of the DC-DC converter, and an output providing an error amplifier output signal representing a difference between the feedback signal and a lower one of the soft start signal and the reference voltage signal, anda comparator circuit comprising a first input receiving the error amplifier output signal, a second input receiving a periodic ramp signal, and an output providing a pulse width modulated output signal according to the error amplifier output signal and the periodic ramp signal; an internal soft start circuit, comprising:
a capacitor amplifier circuit including a first capacitor with a first terminal connected to a first current source and a second terminal connected to a first current mirror circuit to provide a rising voltage at the first terminal of the first capacitor during startup of the control circuit,an output circuit providing a rising internal soft start circuit output signal to the first error amplifier input based at least partially on a voltage across the first capacitor during startup of the control circuit; and an external soft start terminal connected directly to the first error amplifier input to allow connection of an external capacitor between the first error amplifier input and a circuit ground to at least partially control a rise time of a voltage at the first error amplifier input during startup of the control circuit.