A self-excitation push-pull type converter with a transformer having a closed magnetic core or iron core, which formed of a main part (52) and a local part (53). The local part reaches magnetic saturation earlier than the main part under the same increasing magnetic field excitation. When the self-excitation push-pull type converter is in a light load state, the efficiency is significantly improved, and further improved in a rated load state. As the number of turns of the coil on the magnetic saturation transformer is reduced, the working frequency of the converter increases while still keeping the loss low. The probability of generating a current peak at the moments of switching on or off is reduced, thereby further improving the efficiency and reducing output ripples.

A switching power supply apparatus includes a PFM control circuit that outputs a clock signal Set such that a switching frequency of a switching element varies in accordance with a load state. The clock signal Set determines a turn-on timing of the switching element. A reference value of a current flowing through the switching element determines a turn-off timing of the switching element. A modulation signal is applied to the turn-off timing of the switching element to modulate one of a peak value of a drain current flowing through the switching element and an on-time of the switching element. Input control is performed separately on the clock signal Set and the modulation signal. Accordingly, even when the clock signal Set and the modulation signal contribute to each other to offset each other, modulation effects are not cancelled.

A circuit (100) for protecting a Switching Power Converter (SPC) when a short-circuit load condition occurs. The SPC has an output current sensor utilizing at least one current transformer that has a primary winding connected in series with a rectifier and has a magnetic core that should avoid saturation. A pulse-width modulator includes a skip controller providing a series of control pulses to at least one switch. A control pulse is skipped when an abnormally low load resistance causes an input current ramp signal to exceed an input current setpoint signal proximate a start time of a next control pulse of the series and the output current is greater than a predetermined threshold. Operation of the SPC is stopped if more than a predetermined number of consecutive switching cycles are skipped to prevent operation of the SPC while the core of an output current transformer is saturated.

A switching power supply apparatus includes a PFM control circuit that outputs a clock signal Set such that a switching frequency of a switching element varies in accordance with a load state. The clock signal Set determines a turn-on timing of the switching element. A reference value of a current flowing through the switching element determines a turn-off timing of the switching element. A modulation signal is applied to the turn-off timing of the switching element to modulate one of a peak value of a drain current flowing through the switching element and an on-time of the switching element. Input control is performed separately on the clock signal Set and the modulation signal. Accordingly, even when the clock signal Set and the modulation signal contribute to each other to offset each other, modulation effects are not cancelled.

A converter includes a DC input; a transformer including first and second primary windings, first and second secondary windings, and first and second feedback windings; a first field-effect transistor; a second field-effect transistor; and a drive circuit connected to the first and second field-effect transistors. The drive circuit includes a bias circuit that applies a bias voltage to gates of the first and second field-effect transistors via the first and second feedback windings during start-up of the converter, wherein the bias voltage is reduced to zero or substantially zero after start-up of the converter; and a reset circuit that resets the bias circuit when the converter is turned off. The converter is a self-oscillating push-pull DC-DC converter.

A switching power supply apparatus includes a PFM control circuit that outputs a clock signal Set such that a switching frequency of a switching element varies in accordance with a load state. The clock signal Set determines a turn-on timing of the switching element. A reference value of a current flowing through the switching element determines a turn-off timing of the switching element. A modulation signal is applied to the turn-off timing of the switching element to modulate one of a peak value of a drain current flowing through the switching element and an on-time of the switching element. Input control is performed separately on the clock signal Set and the modulation signal. Accordingly, even when the clock signal Set and the modulation signal contribute to each other to offset each other, modulation effects are not cancelled.

A self-excited push-pull converter, where between the bases of the push-pull converter's transistors (TR1, TR2) and the effective power suppler there is provided a constant current source (II), which provides a constant current to the bases of the transistors. With the working voltage increases, the circuit enters into an operating mode not based on the core-saturation working mode, because the transistors' base current is limited by the constant current source and consequently the transistors' collector current cannot increase.

A switching power supply apparatus includes a PFM control circuit that outputs a clock signal Set such that a switching frequency of a switching element varies in accordance with a load state. The clock signal Set determines a turn-on timing of the switching element. A reference value of a current flowing through the switching element determines a turn-off timing of the switching element. A modulation signal is applied to the turn-off timing of the switching element to modulate one of a peak value of a drain current flowing through the switching element and an on-time of the switching element. Input control is performed separately on the clock signal Set and the modulation signal. Accordingly, even when the clock signal Set and the modulation signal contribute to each other to offset each other, modulation effects are not cancelled.

A power converter includes an inductor configured to be coupled with a direct current voltage source. The power converter includes a first switching device coupled with the inductor and a second switching device coupled with the inductor. The first switching device and the second switching device are arranged in parallel. The first switching device and the second switching device have a similar drain resistance.