An AC power source apparatus to be used in an AC corona generator necessary for a de-electrification/separation process, which is one of electrographic image forming processes, or in a case where a low frequency AC power source is required, has a construction such that a high-frequency pulse, whose time ratio is modulated trapezoidally with time, is applied to switching elements connected in inverse-series across a primary winding of a transformer, an inductance element having a regenerative diode and a reset winding is inserted between an intermediate tap of the primary winding of the transformer and a DC power supply input terminal, and an LC filter is formed by stray capacitance of a secondary winding of the transformer, whereby a desired output waveform can be produced with a simple circuit construction.
A method for powering up an integrated circuit and circuit for implementing the method. A first charging current is used to slowly charge a capacitor used in the integrated circuit upon connecting the power. A power-up signal is provided to initialize digital circuitry until the first charging current raises the voltage of the capacitor above a threshold value. Once a capacitor is charged to another predetermined threshold, a second charging current is activated. The two charging currents are thereafter used as the total charging current on the capacitor. If the capacitor is grounded, the initial power-up scheme is re-initiated.
Universal switched power converter having a transformer that comprises a first winding (11-3) divided into two parts and having an intermediate tap (11-3-1), and a second winding (11-9) connected in cascade with rectifier means (12) and filter means (13), so that a first current flows through the part of said first winding (11-3) comprised between the end of the primary winding (11-3) connected to a first input terminal (11-1) and the intermediate tap (11-3-1) and through a second switching element (11-6) connected to the intermediate tap (11-3-1) and to a second input terminal (11-2), when the input voltage applied across the input terminals (11-1, 11-2) is close to a first predetermined voltage value and the second switching element (11-6) is in a conducting state.
Improved controller circuitry for a switching power supply is disclosed. The switching power supply is of the type having a transformer having primary and secondary windings for generating an output voltage at the secondary winding, a power switch for driving the primary winding, and controller circuitry for activating the power switch. The improved controller circuitry includes an oscillator and frequency shift means. The oscillator generates PWM pulses having a predetermined frequency for use in activating the power switch. The frequency shift means gradually shifts the frequency of the PWM pulses at a shift rate in response to the output voltage decreasing to below a threshold level. In another embodiment, a controller for use in a switching power supply includes an oscillator for generating PWM pulses having a predetermined frequency which determine the switching condition of the supply. Frequency shift means is used gradually shifting the frequency of the PWM pulses at a shift rate in response to an output voltage of the switching power supply decreasing to below a threshold level, and programming means is used for programming the shift rate and the threshold level.
