A flyback power converter circuit includes: a transformer; a primary side switch, for controlling a primary winding to convert an input voltage to an output voltage and an internal voltage; a primary side control circuit, which is powered by the internal voltage; the primary side control circuit generates a switching signal according to a feedback signal, to operate the primary side switch; a secondary side control circuit, which generates the feedback signal according the output voltage; and a dummy load circuit, which is coupled to the output voltage, wherein when the output voltage drops to or is lower than a predetermined threshold, the dummy load circuit generates a dummy load current, to determine the feedback signal, so that the internal voltage is not undesirably low. When the output voltage exceeds the predetermined threshold, the dummy load circuit adjusts the dummy load current to zero current.

A flyback power converter circuit includes: a transformer; a primary side switch, for controlling a primary winding to convert an input voltage to an output voltage and an internal voltage; a primary side control circuit, which is powered by the internal voltage; the primary side control circuit generates a switching signal according to a feedback signal, to operate the primary side switch; a secondary side control circuit, which generates the feedback signal according the output voltage; and a dummy load circuit, which is coupled to the output voltage, wherein when the output voltage drops to or is lower than a predetermined threshold, the dummy load circuit generates a dummy load current, to determine the feedback signal, so that the internal voltage is not undesirably low. When the output voltage exceeds the predetermined threshold, the dummy load circuit adjusts the dummy load current to zero current.

A control circuit includes: a transistor controller that controls a voltage at a gate terminal of a field effect transistor in accordance with a difference in voltage between a source terminal and a drain terminal of the field effect transistor connected so that a body diode is in a forward direction; and a current controller that reduces an operating current for operating the transistor controller when a load connected via the source terminal of the field effect transistor is light, and increases the operating current when the load is heavy.

A control circuit includes: a transistor controller that controls a voltage at a gate terminal of a field effect transistor in accordance with a difference in voltage between a source terminal and a drain terminal of the field effect transistor connected so that a body diode is in a forward direction; and a current controller that reduces an operating current for operating the transistor controller when a load connected via the source terminal of the field effect transistor is light, and increases the operating current when the load is heavy.

A power conversion device capable of suppressing current backflow while also improving current responsiveness and power conversion efficiency is achieved. A snubber capacitor capable of absorbing switching surge is connected to a low-voltage side switching circuit that includes switching elements. Until a predetermined time elapses from when a request to start switching is received, a controller determines that the snubber capacitor has not reached full charge or near-full charge, and asynchronously controls the low-voltage side switching circuit and a high-voltage side switching circuit that includes switching elements. After the predetermined time elapses, the controller synchronously controls the low-voltage side switching circuit and the high-voltage side switching circuit, and also controls a duty ratio of the low-voltage side switching circuit and the high-voltage side switching circuit such that current does not flow back from the low-voltage side switching circuit to the high-voltage side switching circuit.

An AC/DC converter is operative to receive, via AC input terminals, an AC input signal and to transform the AC input signal into a DC output signal. The AC/DC converter comprises a first DC discharge circuit coupled to AC input terminals. The controller comprises a second DC discharge circuit having a controllable switching element for switching the second DC discharge circuit on and off. The second DC discharge circuit is operative to receive a DC discharge current from the first DC discharge circuit; logic associated with the AC/DC converter repeatedly: receives a DC sense signal from the second DC discharge circuit and determines, based on the value of the DC sense signal within a predetermined measurement time period, loss of the AC input signal. In response to determining loss of the AC input signal, the logic controls activation of the second DC discharge circuit depending on the DC sense signal.

An AC/DC converter is operative to receive, via AC input terminals, an AC input signal and to transform the AC input signal into a DC output signal. The AC/DC converter comprises a first DC discharge circuit coupled to AC input terminals. The controller comprises a second DC discharge circuit having a controllable switching element for switching the second DC discharge circuit on and off. The second DC discharge circuit is operative to receive a DC discharge current from the first DC discharge circuit; logic associated with the AC/DC converter repeatedly: receives a DC sense signal from the second DC discharge circuit and determines, based on the value of the DC sense signal within a predetermined measurement time period, loss of the AC input signal. In response to determining loss of the AC input signal, the logic controls activation of the second DC discharge circuit depending on the DC sense signal.

A plurality of gate drive circuits each drive a gate of a corresponding one of a plurality of switching elements included in a converter and an inverter. Each gate drive circuit includes a gate driver and a power source circuit. The gate driver drives the gate potential of the switching element to a potential corresponding to H or L level, in accordance with the gate signal input from a controller to the gate electrode of the switching element. The power source circuit supplies power to the gate driver. When a first switch is ON and a second switch is OFF, the controller, upon detection of an abnormality of the power source circuit of the gate drive circuit, turns on the second switch and turns off the first switch. The gate drive circuit maintains the gate potential of the switching element during the period from when the abnormality of the power source circuit is detected to when the second switch is turned on.

A plurality of gate drive circuits each drive a gate of a corresponding one of a plurality of switching elements included in a converter and an inverter. Each gate drive circuit includes a gate driver and a power source circuit. The gate driver drives the gate potential of the switching element to a potential corresponding to H or L level, in accordance with the gate signal input from a controller to the gate electrode of the switching element. The power source circuit supplies power to the gate driver. When a first switch is ON and a second switch is OFF, the controller, upon detection of an abnormality of the power source circuit of the gate drive circuit, turns on the second switch and turns off the first switch. The gate drive circuit maintains the gate potential of the switching element during the period from when the abnormality of the power source circuit is detected to when the second switch is turned on.

A control circuit includes: a transistor controller that controls a voltage at a gate terminal of a field effect transistor in accordance with a difference in voltage between a source terminal and a drain terminal of the field effect transistor connected so that a body diode is in a forward direction; and a current controller that reduces an operating current for operating the transistor controller when a load connected via the source terminal of the field effect transistor is light, and increases the operating current when the load is heavy.