Integrated circuit and power supply circuit
An integrated circuit for a power supply circuit that includes a transformer, a transistor and a capacitor. The power supply circuit generates an output voltage from an AC voltage. The integrated circuit drives the transistor, and includes: a terminal connected to the capacitor and receiving a power supply voltage; a mode detection circuit detecting whether an operation mode of the power supply circuit is a first mode or a second mode; a discharge circuit discharging the capacitor and lowering the power supply voltage to a first level, when the operation mode is the first mode; and a drive signal output circuit outputting, to the transistor, a drive signal that is at a level of the power supply voltage, and at a predetermined level lower than the level of the power supply voltage, when the operation mode is detected to be the first mode and the second mode, respectively.
1 . An integrated circuit for a power supply circuit that includes a transformer including a primary coil, a secondary coil, and an auxiliary coil, a transistor configured to control a current flowing through the primary coil, and a first capacitor configured to receive a power supply voltage corresponding to a coil voltage at the auxiliary coil, the power supply circuit being configured to operate in an operation mode to generate an output voltage from an alternating current (AC) voltage, the operation mode being either a first mode, in which the generated output voltage is at a first target level, or a second mode, in which the generated output voltage is at a second target level higher than the first target level, the integrated circuit being configured to drive the transistor, the integrated circuit comprising: a first terminal connected to the first capacitor, the first terminal being configured to receive the power supply voltage corresponding to the coil voltage at the auxiliary coil; a mode detection circuit configured to detect whether the operation mode of the power supply circuit is the first mode or the second mode; a discharge circuit configured to discharge the first capacitor and lower a level of the power supply voltage to a first level, when it is detected that the operation mode is the first mode; and a drive signal output circuit configured to output a drive signal to the transistor, the drive signal being at a level of the power supply voltage, when the operation mode is detected to be the first mode, and at a predetermined level lower than the level of the power supply voltage, when the operation mode is detected to be the second mode.
2 . The integrated circuit according to claim 1 , wherein the drive signal output circuit includes
a driver circuit configured to output the drive signal, based on the power supply voltage, and
a limiter circuit configured to limit a level of the drive signal to the predetermined level, when the operation mode is detected to be the second mode.
3 . The integrated circuit according to claim 2 , further comprising:
a timer configured to measure a predetermined time period, when the operation mode is detected to be the first mode, wherein
the limiter circuit limits the level of the drive signal to the predetermined level, until the predetermined time period has elapsed since the operation mode is detected to be the first mode.
4 . The integrated circuit according to claim 2 , further comprising:
a second detection circuit configured to detect whether the level of the power supply voltage has dropped to the first level, wherein
the limiter circuit limits the level of the drive signal to the predetermined level, until the level of the power supply voltage drops to the first level after the operating mode is detected to be the first mode.
5 . The integrated circuit according to claim 1 , further comprising:
a determination circuit configured to determine whether the level of the power supply voltage has dropped below a second level lower than the first level, wherein
the drive signal output circuit stops operating, in response to the power supply voltage dropping below the second level.
6 . The integrated circuit according to claim 5 , wherein the drive signal output circuit outputs the drive signal to the transistor such that the level of the power supply voltage exceeds the second level.
7 . The integrated circuit according to claim 5 , further comprising:
a second terminal configured to receive a voltage corresponding to the AC voltage;
a first detection circuit configured to detect whether the level of the power supply voltage is below a third level higher than the second level; and
a charging circuit configured to charge the first capacitor, based on the voltage received at the second terminal, so as to, in response to the power supply voltage becoming below the third level, increase the level of the power supply voltage to exceed the third level.
8 . The integrated circuit according to claim 1 , wherein
the power supply circuit further includes a second capacitor, and
the integrated circuit further includes a third terminal to which the second capacitor is connected, and
the third terminal is configured to
receive a voltage corresponding to a current flowing through the transistor, when the transistor is on, and
receive a voltage corresponding to the coil voltage, when the transistor is off, wherein
the mode detection circuit detects whether the operation mode of the power supply circuit is the first mode or the second mode, based on the voltage received at the third terminal when the transistor is off.
9 . The integrated circuit according to claim 1 , wherein
the power supply circuit further includes a third capacitor, and
the integrated circuit further includes a fourth terminal to which the third capacitor is connected, the fourth terminal being configured to receive a voltage corresponding to the coil voltage, wherein
the mode detection circuit detects whether the operation mode of the power supply circuit is the first mode or the second mode, based on the voltage received at the fourth terminal.
10 . A power supply circuit configured to operate in an operation mode to generate an output voltage from an alternating current (AC) voltage, the operation mode being either a first mode, in which the generated output voltage is at a first target level, or a second mode, in which the generated output voltage is at a second target level higher than the first target level, the power supply circuit comprising: a transformer including a primary coil, a secondary coil, and an auxiliary coil; a transistor configured to control a current flowing through the primary coil; a first capacitor configured to receive a power supply voltage corresponding to a coil voltage at the auxiliary coil; and an integrated circuit configured to drive the transistor, the integrated circuit including a first terminal connected to the first capacitor, the first terminal being configured to receive the power supply voltage corresponding to the coil voltage at the auxiliary coil, a mode detection circuit configured to detect whether the operation mode of the power supply circuit is the first mode or the second mode, a discharge circuit configured to discharge the first capacitor and lower a level of the power supply voltage to a first level, upon detecting that the operation mode is the first mode, and a drive signal output circuit configured to output a drive signal to the transistor, the drive signal being at the level of the power supply voltage, when the operation mode is detected to be the first mode, and at a predetermined level lower than the level of the power supply voltage, when the operation mode is detected to be the second mode.