Switching control circuit and power supply circuit

Abstract

To provide a switching control circuit that can properly drive transistors. [Solution] The switching control circuit includes an inductor to which a rectified voltage corresponding to an AC voltage is applied, and a transistor that controls the inductor current flowing through the inductor, and further includes a detection circuit that detects whether the inductor current has reached a predetermined value, a timing circuit that measures the period after the inductor current has reached the predetermined value, and a drive circuit that turns on the transistor when the number of times the inductor current has reached the predetermined value reaches a predetermined number of times, and turns off the transistor when an on period corresponding to the output voltage has elapsed, wherein the drive circuit turns on the transistor when the period is a first predetermined period when the effective value of the AC voltage is at a first level, and turns on the transistor when the period is a second predetermined period shorter than the first predetermined period when the effective value of the AC voltage is at a second level higher than the first level.

Claims

1. A switching control circuit for a power supply circuit that generates an output voltage from the AC voltage, comprising an inductor to which a rectified voltage corresponding to an AC voltage is applied, and a transistor that controls the inductor current flowing through the inductor, wherein the switching control circuit controls the switching of the transistor, A detection circuit for detecting whether the inductor current has reached a predetermined value, A timing circuit that measures the period after the inductor current reaches the predetermined value, A drive circuit that turns on the transistor when the number of times the inductor current reaches the predetermined value reaches a predetermined number of times, and turns off the transistor when an on period corresponding to the output voltage has elapsed, Equipped with, The aforementioned drive circuit is When the effective value of the AC voltage is at a first level, the transistor is turned on when the period becomes a first predetermined period. When the effective value of the AC voltage is at a second level higher than the first level, the transistor is turned on when the period becomes a second predetermined period shorter than the first predetermined period. Switching control circuit.

2. A switching control circuit according to claim 1, Each of the first and second predetermined periods is the period from when the transistor is turned off until the voltage between the first and second electrodes of the transistor reaches its lowest point. Switching control circuit.

3. A switching control circuit according to claim 1 or claim 2, A calculation circuit that calculates the AC voltage based on the ON period and OFF period of the transistor. Equipped with, The aforementioned drive circuit is Based on the calculation results of the calculation circuit, an output circuit outputs a first predetermined period when the effective value of the AC voltage is at the first level, and outputs a second predetermined period when the effective value of the AC voltage is at the second level. An on / off circuit that turns on the transistor when the aforementioned period is the period during which output is produced from the output circuit, and turns off the transistor when the on period has elapsed, A switching control circuit equipped with the following features.

4. A switching control circuit for a power supply circuit that generates an output voltage from the AC voltage, comprising an inductor to which a rectified voltage corresponding to an AC voltage is applied, and a transistor that controls the inductor current flowing through the inductor, wherein the switching control circuit controls the switching of the transistor, A detection circuit for detecting whether the inductor current has reached a predetermined value, A timing circuit that measures the period after the inductor current reaches the predetermined value, A drive circuit that turns on the transistor when the number of times the inductor current reaches the predetermined value reaches a predetermined number of times, or when the predetermined period has elapsed, and turns off the transistor when the on period corresponding to the output voltage has elapsed. Equipped with, The aforementioned drive circuit is When the aforementioned period reaches the predetermined period, the transistor is turned on at the timing when the voltage between the first and second electrodes of the transistor reaches its lowest point. Switching control circuit.

5. A power supply circuit that generates an output voltage from an AC voltage, An inductor to which a rectified voltage corresponding to an AC voltage is applied, A transistor that controls the inductor current flowing through the aforementioned inductor, A switching control circuit for controlling the switching of the transistor, Equipped with, The aforementioned switching control circuit is A detection circuit for detecting whether the inductor current has reached a predetermined value, A timing circuit that measures the period after the inductor current reaches the predetermined value, A drive circuit that turns on the transistor when the number of times the inductor current reaches the predetermined value reaches a predetermined number of times, and turns off the transistor when an on period corresponding to the output voltage has elapsed, Includes, The aforementioned drive circuit is When the effective value of the AC voltage is at a first level, the transistor is turned on when the period becomes a first predetermined period. When the effective value of the AC voltage is at a second level higher than the first level, the transistor is turned on when the period becomes a second predetermined period shorter than the first predetermined period. power circuit.

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