Switching control circuit and power supply circuit

Patent metadata

Field	Value
Publication number	US-2025202367-A1
Application number	US-202418932327-A
Country	US
Kind code	A1
Filing date	Oct 30, 2024
Priority date	Dec 13, 2023
Publication date	Jun 19, 2025
Grant date	—

Abstract

A switching control circuit for controlling switching of first and second transistors of a power supply circuit. The switching control circuit including: a load detection circuit detecting a state of a load; a drive signal output circuit outputting a drive signal that causes the power supply circuit to operate in a burst mode and a normal mode respectively when the load is light and heavy loads. The drive signal output circuit operates in a first state in which the drive signal is outputted based on a predetermined condition, a second state in which the drive signal is outputted to gradually reduce an ON period of the first and second transistors and a third state in which outputting of the drive signal is stopped, and enters the third state from the first state without going through the second state immediately after the power supply circuit starts operating in the burst mode.

First claim

What is claimed is:

1 . A switching control circuit for a power supply circuit that generates an output voltage of a target level from an input voltage thereof, the power supply circuit including
a transformer including a primary coil, a secondary coil, and an auxiliary coil, a first transistor and a second transistor configured to control a current of the primary coil, and a first capacitor that forms a resonant circuit with the primary coil,
the switching control circuit being configured to control switching of the first transistor and the second transistor, the switching control circuit comprising:
a load detection circuit configured to detect a state of a load of the power supply circuit, based on a resonant current flowing through the resonant circuit; and
a drive signal output circuit configured to output a drive signal, which
causes the power supply circuit to operate in a burst mode when the load is in a light-load state, and
causes the power supply circuit to operate in a normal mode when the load is in a heavy-load state, wherein

the drive signal output circuit is configured to operate in:
a first state, in which the drive signal is outputted based on a predetermined condition,
a second state, in which the drive signal is outputted to gradually reduce an ON period of the first transistor and the second transistor, and
a third state, in which an output of the drive signal is stopped; and

the drive signal output circuit is further configured to enter the third state from the first state without going through the second state, immediately after the power supply circuit starts operating in the burst mode.

2 . The switching control circuit according to claim 1 , wherein
the drive signal output circuit is further configured to operate in a fourth state, in which the drive signal is outputted to gradually increase the ON period of the first transistor and the second transistor, and the drive signal output circuit is further configured to repeat a sequence of operating in the third state, in the fourth state, in the first state, and in the second state, immediately after the power supply circuit starts operating in the burst mode.

3 . The switching control circuit according to claim 2 , further comprising:
a detection circuit configured to detect a polarity of the resonant current; and a comparator circuit configured to compare a magnitude between each of a plurality of threshold values determined based on the input voltage and a voltage corresponding to a voltage at the auxiliary coil, wherein the drive signal output circuit is further configured to
output the drive signal based on a result of detection of the detection circuit and a feedback voltage corresponding to the output voltage, when the power supply circuit is operating in the normal mode, and
output the drive signal based on the predetermined condition that is determined based on a result of comparison of the comparator circuit, when the power supply circuit is operating in the first state in the burst mode.

4 . The switching control circuit according to claim 3 , wherein the drive signal output circuit is further configured to, in the second state, reduce an amount of change in the ON period of the first transistor and the second transistor, in response to the input voltage rising.

5 . The switching control circuit according to claim 4 , wherein the drive signal output circuit is further configured to, in the fourth state, reduce an amount of change in the ON period of the first transistor and the second transistor, in response to the input voltage rising.

6 . A switching control circuit for a power supply circuit that generates an output voltage of a target level from an input voltage thereof, the power supply circuit including
a transformer including a primary coil, a secondary coil, and an auxiliary coil, a first transistor and a second transistor configured to control a current flowing through the primary coil, and a first capacitor that forms a resonant circuit with the primary coil,
the switching control circuit being configured to control switching of the first transistor and the second transistor, the switching control circuit comprising:
a load detection circuit configured to detect a state of a load of the power supply circuit, based on a resonant current flowing through the resonant circuit; and
a drive signal output circuit configured to output a drive signal, which
causes the power supply circuit to operate in a burst mode when the load is in a light-load state, and
causes the power supply circuit to operate in a normal mode when the load is in a heavy-load state, wherein

the drive signal output circuit is configured to operate in:
a first state, in which the drive signal is outputted based on a predetermined condition,
a second state, in which the drive signal is outputted to gradually reduce an ON period of the first transistor and the second transistor,
a third state, in which an output of the drive signal is stopped, and
a fourth state, in which the drive signal is outputted to gradually increase the ON period of the first transistor and the second transistor, and the drive signal output circuit is further configured to
repeat an operation of entering the first state, the second state, the third state, and the fourth state, and
reduce an amount of change in the ON period of the first transistor and the second transistor, in response to the input voltage rising, in each of the second state and the fourth state.

7 . A power supply circuit configured to generate an output voltage of a target level from an input voltage thereof, the power supply circuit comprising:
a transformer including a primary coil, a secondary coil, and an auxiliary coil; a first transistor and a second transistor configured to control a current flowing through the primary coil; a first capacitor that forms a resonant circuit with the primary coil; and a switching control circuit configured to control switching of the first transistor and the second transistor, the switching control circuit including:
a load detection circuit configured to detect a state of a load of the power supply circuit, based on a resonant current flowing through the resonant circuit; and
a drive signal output circuit configured to output a drive signal, which
causes the power supply circuit to operate in a burst mode when the load is in a light-load state, and
causes the power supply circuit to operate in a normal mode when the load is in a heavy-load state, wherein
the drive signal output circuit is configured to operate in:
a first state, in which the drive signal is outputted based on a predetermined condition,
a second state, in which the drive signal is outputted to gradually reduce an ON period of the first transistor and the second transistor, and
a third state, in which an output of the drive signal is stopped; and

the drive signal output circuit is further configured to enter the third state from the first state, without going through the second state, immediately after the power supply circuit starts operating in the burst mode.

8 . A switching control circuit for a power supply circuit that generates an output voltage of a target level from an input voltage thereof, the power supply circuit including
a transformer including a primary coil, a secondary coil, and an auxiliary coil, a first transistor and a second transistor configured to control a current flowing through the primary coil, and a first capacitor that forms a resonant circuit with the primary coil,
the switching control circuit being configured to control switching of the first transistor and the second transistor, the switching control circuit co

Assignees

• Fuji Electric Co Ltd

Inventors

• Kobayashi Yoshinori

Classifications

• H02M3/01

  Resonant DC/DC converters · CPC title

• H02M3/33569 Primary

  having several active switching elements (H02M3/3353 takes precedence) · CPC title

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• H02M1/0038

  Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control · CPC title

• H02M1/32 Primary

  Means for protecting converters other than automatic disconnection · CPC title