Abstract: A switching power supply includes a SiC MOSFET (a main switching device) that switches a main current flowing through a primary coil of a transformer ON and OFF as well as a Si MOSFET (a secondary switching device) that has a lower power capacity than the main switching device and is arranged in parallel therewith. A control circuit includes a driver circuit that respectively switches the main switching device and the secondary switching device ON and OFF on the basis of a control signal generated in accordance with an output voltage obtained from a secondary coil of the transformer. The control circuit further includes an enable control circuit that disables the ON/OFF switching of the main switching device when a voltage of an auxiliary voltage obtained from an auxiliary coil of the transformer is less than a prescribed threshold voltage.

Abstract: A switching power supply apparatus includes a switching circuit, a resonance circuit, a rectifying circuit, and a control circuit. The switching circuit includes switching elements connected in series between input terminals of a source. The resonance circuit includes an excitation inductor of a primary winding of a transformer, a resonance inductor connected in series with the excitation inductor, and a variable resonance capacitor which is connected in series with the excitation inductor and whose electrostatic capacity changes according to a control voltage. The control circuit generates, on the basis of a feedback voltage, switching signals in which frequency diffusion is given to a switching frequency and the control voltage and outputs the switching signals and the control voltage to simultaneously change the switching frequency and the electrostatic capacity of the variable resonance capacitor.

Abstract: A switching power supply includes a SiC MOSFET (a main switching device) that switches a main current flowing through a primary coil of a transformer ON and OFF as well as a Si MOSFET (a secondary switching device) that has a lower power capacity than the main switching device and is arranged in parallel therewith. A control circuit includes a driver circuit that respectively switches the main switching device and the secondary switching device ON and OFF on the basis of a control signal generated in accordance with an output voltage obtained from a secondary coil of the transformer. The control circuit further includes an enable control circuit that disables the ON/OFF switching of the main switching device when a voltage of an auxiliary voltage obtained from an auxiliary coil of the transformer is less than a prescribed threshold voltage.

Abstract: A multi-output power supply includes: a switching element that turns ON and OFF currents flowing through all primary coils of a plurality of transformers connected in parallel at a same time; a plurality of output circuits that rectify and smooth voltages induced in secondary coils of the plurality of transformers to produce a plurality of output voltages; a plurality of feedback voltage detection circuits that detect feedback voltages corresponding to the output voltages of the plurality of the output circuits; an averaging circuit that calculates an average feedback voltage from the feedback voltages detected by the feedback voltage detection circuits; and a control circuit that uses feedback control to turn the switching element ON and OFF according to the average feedback voltage calculated by the averaging circuit.

Abstract: A conducted EMI noise reduction effect close to that achieved by using an optimal modulating waveform as a modulating wave is achieved when employing a frequency spreading technique as a measure against noise when a conducted EMI standard is extended to a low-frequency range. A triangular wave/Hershey's Kiss approximation signal generating unit and a triangular wave generation control unit generate a fundamental triangular wave by a transistor charging a capacitor with a current and a transistor discharging the current from the capacitor. A slope switching signal generating unit generates signals expressing the start and end of a charge period and the start and end of a discharge period. An additional charge or additional discharge is carried out in response to the signals turning a transistor on, and the slope of the triangular wave temporarily increases in that period only.

Abstract: A switching power supply includes a switching element that turns ON and OFF a current flowing through a primary coil of a transformer to which a DC input voltage is applied, an output circuit that rectifies and smooths a voltage induced in a secondary coil of the transformer T to generate a prescribed output voltage, and a control circuit that uses feedback control to turn the switching element ON and OFF according to a feedback voltage obtained from the detected output voltage. The switching power supply also includes a supply voltage generation circuit that rectifies and smoothes a voltage induced in an auxiliary coil of the transformer to generate a plurality of supply voltages, an output voltage switching circuit that switches the output voltage according to a magnitude of a load to which the output voltage is supplied, and a supply voltage switching circuit that selects one of the supply voltages according to changes to the output voltage and supplies that supply voltage to the control circuit.

Abstract: A switching power supply device enables measures against noise even when the conducted EMI standard is expanded to a low frequency region. A jitter control circuit, configured so as to reduce generation of conducted EMI noise by giving jitter (frequency diffusion) to a switching frequency which drives a switching element, upon receiving a feedback voltage representing the condition of a load, expands the diffusion width of the switching frequency in stages in accordance with a shift from a fixed frequency region of a maximum oscillation frequency, through a frequency reduction region, to a fixed frequency region of a minimum oscillation frequency. By so doing, it is possible to obtain the effect of sufficient reduction of EMI noise even when an EMI noise measurement frequency range is expanded to a low frequency side.

Abstract: A switching power supply apparatus includes a switching circuit, a resonance circuit, a rectifying circuit, and a control circuit. The switching circuit includes switching elements connected in series between input terminals of a source. The resonance circuit includes an excitation inductor of a primary winding of a transformer, a resonance inductor connected in series with the excitation inductor, and a variable resonance capacitor which is connected in series with the excitation inductor and whose electrostatic capacity changes according to a control voltage. The control circuit generates, on the basis of a feedback voltage, switching signals in which frequency diffusion is given to a switching frequency and the control voltage and outputs the switching signals and the control voltage to simultaneously change the switching frequency and the electrostatic capacity of the variable resonance capacitor.

Abstract: A switching power supply includes a main switching element that is connected to a primary coil of a transformer and switches a main current ON/OFF, and a secondary switching element connected in parallel to the main switching element and that has a lower power capacity than the main switching element. The switching power supply also includes a control circuit that controls these switching elements. The control circuit includes: a main driver circuit that generates, in accordance with a control signal generated according to an output voltage from a secondary coil of the transformer, a main drive signal for switching the main switching element ON/OFF; a secondary driver circuit that generates a secondary drive signal for switching the secondary switching element ON/OFF according to the control signal; and an enable control circuit that deactivates the main driver circuit when a power consumption of a load is less than a threshold value.

Abstract: A jitter control circuit, which reduces conducted EMI noise by giving jitter (frequency diffusion) to the operating frequency for driving a switching element, determines an operating frequency fc (e.g., 40 kHz) at which reduction effects change from a feedback voltage that represents magnitude of a load. The jitter control circuit causes a, for example, 8-bit counter that generates a modulation frequency to operate with, for example, 8 bits when 40 kHz?fc and 7 bits when fc<40 kHz. In this way, even when the range of the EMI noise measurement frequency is extended to the lower frequency side, for example, to 25 kHz, the maximum reduction effect is maintained in the entire frequency range. Thus, the maximum EMI noise reduction effect is obtained.

Abstract: A conducted EMI noise reduction effect close to that achieved by using an optimal modulating waveform as a modulating wave is achieved when employing a frequency spreading technique as a measure against noise when a conducted EMI standard is extended to a low-frequency range. A triangular wave/Hershey's Kiss approximation signal generating unit and a triangular wave generation control unit generate a fundamental triangular wave by a transistor charging a capacitor with a current and a transistor discharging the current from the capacitor. A slope switching signal generating unit generates signals expressing the start and end of a charge period and the start and end of a discharge period. An additional charge or additional discharge is carried out in response to the signals turning a transistor on, and the slope of the triangular wave temporarily increases in that period only.

Abstract: A jitter control circuit, which reduces conducted EMI noise by giving jitter (frequency diffusion) to the operating frequency for driving a switching element, determines an operating frequency fc (e.g., 40 kHz) at which reduction effects change from a feedback voltage that represents magnitude of a load. The jitter control circuit causes a, for example, 8-bit counter that generates a modulation frequency to operate with, for example, 8 bits when 40 kHz?fc and 7 bits when fc<40 kHz. In this way, even when the range of the EMI noise measurement frequency is extended to the lower frequency side, for example, to 25 kHz, the maximum reduction effect is maintained in the entire frequency range. Thus, the maximum EMI noise reduction effect is obtained.

Abstract: A switching power supply includes a main switching element that is connected to a primary coil of a transformer and switches a main current ON/OFF, and a secondary switching element connected in parallel to the main switching element and that has a lower power capacity than the main switching element. The switching power supply also includes a control circuit that controls these switching elements. The control circuit includes: a main driver circuit that generates, in accordance with a control signal generated according to an output voltage from a secondary coil of the transformer, a main drive signal for switching the main switching element ON/OFF; a secondary driver circuit that generates a secondary drive signal for switching the secondary switching element ON/OFF according to the control signal; and an enable control circuit that deactivates the main driver circuit when a power consumption of a load is less than a threshold value.

Abstract: An output voltage detection portion detects the change of a DC output voltage on a primary side of a transformer. A control circuit outputs a gate signal of a frequency corresponding to the detected change to stabilize the DC output voltage. A load transient detection portion includes capacitors and a capacitor and/or a resistor. The load transient detection portion detects the decrease of the DC output voltage caused by a load transient. Thus, when the control circuit is performing switching control in a long cycle under a light load, the load transient detection portion can detect a timing of the load transient without waiting until the next cycle switching so that the control circuit can vary the frequency of the gate signal to a frequency corresponding to a heavy load. Accordingly, it is possible to suppress the decrease of the DC output voltage at the time of the load transient.

Abstract: A bypass switch is connected in parallel to an inductor of a power supply circuit for a control circuit connected to an auxiliary coil, and an output voltage detection circuit connected to the auxiliary coil detects a load state of the secondary side of a transformer. In a control circuit, an error amplifier and a capacitor generate a voltage (an error signal) corresponding to the load state from the difference between a voltage sampled from a signal detected by the output voltage detection circuit by a sample and hold circuit and a reference voltage. A comparator switches the switch OFF when the load is heavy and switches the switch ON when the load is light. This makes it possible to ignore the effect of the inductor when the load is light, and therefore only the heavy load state needs to be considered to keep the output voltage of the secondary side adjusted appropriately.

Abstract: A bypass switch is connected in parallel to an inductor of a power supply circuit for a control circuit connected to an auxiliary coil, and an output voltage detection circuit connected to the auxiliary coil detects a load state of the secondary side of a transformer. In a control circuit, an error amplifier and a capacitor generate a voltage (an error signal) corresponding to the load state from the difference between a voltage sampled from a signal detected by the output voltage detection circuit by a sample and hold circuit and a reference voltage. A comparator switches the switch OFF when the load is heavy and switches the switch ON when the load is light. This makes it possible to ignore the effect of the inductor when the load is light, and therefore only the heavy load state needs to be considered to keep the output voltage of the secondary side adjusted appropriately.

Abstract: A switching power supply device enables measures against noise even when the conducted EMI standard is expanded to a low frequency region. A jitter control circuit, configured so as to reduce generation of conducted EMI noise by giving jitter (frequency diffusion) to a switching frequency which drives a switching element, upon receiving a feedback voltage representing the condition of a load, expands the diffusion width of the switching frequency in stages in accordance with a shift from a fixed frequency region of a maximum oscillation frequency, through a frequency reduction region, to a fixed frequency region of a minimum oscillation frequency. By so doing, it is possible to obtain the effect of sufficient reduction of EMI noise even when an EMI noise measurement frequency range is expanded to a low frequency side.

Abstract: A switching power supply includes a switching element that turns ON and OFF a current flowing through a primary coil of a transformer to which a DC input voltage is applied, an output circuit that rectifies and smooths a voltage induced in a secondary coil of the transformer T to generate a prescribed output voltage, and a control circuit that uses feedback control to turn the switching element ON and OFF according to a feedback voltage obtained from the detected output voltage. The switching power supply also includes a supply voltage generation circuit that rectifies and smoothes a voltage induced in an auxiliary coil of the transformer to generate a plurality of supply voltages, an output voltage switching circuit that switches the output voltage according to a magnitude of a load to which the output voltage is supplied, and a supply voltage switching circuit that selects one of the supply voltages according to changes to the output voltage and supplies that supply voltage to the control circuit.

Abstract: A multi-output power supply includes: a switching element that turns ON and OFF currents flowing through all primary coils of a plurality of transformers connected in parallel at a same time; a plurality of output circuits that rectify and smooth voltages induced in secondary coils of the plurality of transformers to produce a plurality of output voltages; a plurality of feedback voltage detection circuits that detect feedback voltages corresponding to the output voltages of the plurality of the output circuits; an averaging circuit that calculates an average feedback voltage from the feedback voltages detected by the feedback voltage detection circuits; and a control circuit that uses feedback control to turn the switching element ON and OFF according to the average feedback voltage calculated by the averaging circuit.

Abstract: An isolated switching power supply can include a switching element connected to an input power supply, a control circuit that ON/OFF-drives the switching element and generates an AC power in a secondary winding and in an auxiliary winding of the isolation transformer, an output circuit that rectifies the AC power generated in the on a secondary winding of the isolation transformer and outputs the rectified power, an internal power supply circuit that generates a driving power supply voltage for the control circuit from the AC power generated in the auxiliary winding, an output voltage detecting circuit that feeds back an output monitoring voltage obtained from the driving power supply voltage to the control circuit to control the ON/OFF driving of the switching element by the control circuit and an output voltage controller that changes a level of the output monitoring voltage obtained from the driving power supply voltage.