Switching control circuit and power supply circuit

Patent metadata

Field	Value
Publication number	US-2025293579-A1
Application number	US-202519041782-A
Country	US
Kind code	A1
Filing date	Jan 30, 2025
Priority date	Mar 12, 2024
Publication date	Sep 18, 2025
Grant date	—

Abstract

A switching control circuit for controlling a power supply circuit, including: a comparator circuit comparing each of a first voltage and a second voltage with a feedback voltage corresponding to an output voltage; a first adjustment circuit adjusting the first voltage; and a drive signal output circuit outputting a drive signal to operate the power supply circuit in a normal mode and in a burst mode, respectively in response to a state of the load entering a light-load state and a light-load state. The drive signal output circuit outputs the drive signal to gradually increase an ON period of each of the first transistor and the second transistor, in response to the feedback voltage exceeding the first voltage, and to gradually reduce the ON period of each of the first transistor and the second transistor, in response to the feedback voltage dropping below the second voltage.

First claim

What is claimed is:

1 . A switching control circuit for controlling a power supply circuit that generates an output voltage at a target level on a secondary side 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 that are 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 comparator circuit configured to compare each of a first voltage and a second voltage lower than the first voltage, with a feedback voltage corresponding to the output voltage;
a first adjustment circuit configured to adjust a level of the first voltage; and
a drive signal output circuit configured to
output a drive signal to operate the power supply circuit in a normal mode, in response to a state of a load of the power supply circuit entering a heavy-load state, and
output the drive signal to operate the power supply circuit in a burst mode, in response to the state of the load entering a light-load state, wherein
the drive signal output circuit
enters a first state of outputting the drive signal to gradually increase an ON period of each of the first transistor and the second transistor, in response to the feedback voltage exceeding the first voltage, and
enters a second state of outputting the drive signal to gradually reduce the ON period of each of the first transistor and the second transistor, in response to the feedback voltage dropping below the second voltage.

2 . The switching control circuit according to claim 1 , wherein
the drive signal output circuit is further configured to
output the drive signal to operate the power supply circuit in the normal mode, in response to the feedback voltage reaching a third voltage, and
output the drive signal to operate the power supply circuit in the burst mode, in response to the feedback voltage reaching a fourth voltage lower than the third voltage; and
the first voltage is lower than the fourth voltage.

3 . The switching control circuit according to claim 2 , further comprising:
a resonant current amount detection circuit configured to detect a magnitude of a resonant current flowing through the resonant circuit, wherein in response to the resonant current amount detection circuit detecting that the magnitude of the resonant current is equal to a first predetermined amount, the drive signal output circuit outputs the drive signal to cause the power supply circuit to operate in the normal mode, and in response to the resonant current amount detection circuit detecting that the magnitude of the resonant current is equal to a second predetermined amount, and the feedback voltage reaching the fourth voltage, the drive signal output circuit outputs the drive signal to cause the power supply circuit to operate in the burst mode.

4 . The switching control circuit according to claim 1 , wherein the drive signal output circuit enters the first state and the second state when the power supply circuit operates in the burst mode.

5 . The switching control circuit according to claim 1 , wherein
the drive signal output circuit is further configured to operate in a third state between the first state and the second state, the third state being a state of outputting the drive signal to set the ON period of each of the first transistor and the second transistor according to a voltage of the auxiliary coil, and the drive signal output circuit transitions from the first state to the third state, in response to the ON period of each of the first transistor and the second transistor determined according to the voltage of the auxiliary coil becoming shorter than the ON period of each of the first transistor and the second transistor in the first state.

6 . The switching control circuit according to claim 5 , wherein the drive signal output circuit controls switching of the first transistor and the second transistor so as to have
a switching operation period of transitioning from the first state to the second state through the third state, and a stop operation period of stopping the switching the first transistor and the second transistor,
when the power supply circuit operates in the burst mode.

7 . The switching control circuit according to claim 6 , wherein the stop operation period is included in a time period from completion of the second state to start of the first state.

8 . The switching control circuit according to claim 5 , wherein the drive signal output circuit transitions from the third state to the second state, in response to the ON period of each of the first transistor and the second transistor in the second state becoming shorter than the ON period of each of the first transistor and the second transistor determined according to a voltage of the auxiliary coil.

9 . The switching control circuit according to claim 1 , further comprising:
a setting circuit configured to receive first data indicating the level of the first voltage, wherein the first adjustment circuit adjusts the level of the first voltage, based on the first data.

10 . The switching control circuit according to claim 9 , further comprising:
a second adjustment circuit configured to adjust a level of the second voltage.

11 . The switching control circuit according to claim 10 , wherein
the setting circuit receives second data indicating the level of the second voltage, and the second adjustment circuit adjusts the level of the second voltage, based on the second data.

12 . The switching control circuit according to claim 1 , wherein
the switching control circuit is an integrated circuit including
a first terminal to which a resistor is connected, and
a constant current circuit configured to supply a predetermined current to the resistor, and
the first adjustment circuit adjusts the level of the first voltage, based on a voltage of the resistor.

13 . The switching control circuit according to claim 12 , further comprising a second adjustment circuit configured to adjust a level of the second voltage.

14 . The switching control circuit according to claim 13 , wherein the second adjustment circuit adjusts the level of the second voltage, based on a voltage of the resistor.

15 . The switching control circuit according to claim 1 , further comprising
a detection circuit configured to detect a resonant current flowing through the resonant circuit, wherein the drive signal output circuit outputs the drive signal, based on a result of detection of the detection circuit and the feedback voltage, when the power supply circuit is operating in the normal mode.

16 . A power supply circuit configured to generate an output voltage at a target level on a secondary side 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 that are configured to control a current of the primary coil; a first capacitor forming a resonant circuit with the primary coil; and a switching control circuit configured to control switching of the first transistor and the second transistor, wherein the switching control circuit includes
a comparator circuit configured to compare each of a first voltage and a second voltage lower than the first voltag

Assignees

• Fuji Electric Co Ltd

Inventors

• Kobayashi Yoshinori

Classifications

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title

• H02M1/0035 Primary

  using burst mode control · CPC title

• H02M1/38

  Means for preventing simultaneous conduction of switches · CPC title

• H02M3/33523

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H02M3/33571

  Half-bridge at primary side of an isolation transformer · CPC title