Integrated circuits and power supply circuits

Abstract

To provide an integrated circuit that controls a transistor of a power source circuit suitably in accordance with the state of a load.SOLUTION: An integrated circuit includes: a first comparison circuit that compares a first voltage according to the voltage on a high potential side of a transistor and a second voltage; an oscillation circuit that outputs an oscillation signal; and a switching control circuit that controls switching. The switching control circuit includes: an on-signal output circuit that receives input of the oscillation signal in a discontinuous mode in which the current of a secondary coil of a transformer is zero when the transistor is off, and outputs an on-signal to turn on the transistor after a first number of times that the first voltage becomes the second voltage reaches a reference number of times; an off-signal output circuit that outputs an off-signal to turn off the transistor on the basis of the current flowing in the transistor; a first holding circuit that holds the reference number of times; and an adjustment circuit that increases the reference number of times when a load current flowing in the load decreases, and decreases the reference number of times when the load current increases.SELECTED DRAWING: Figure 2

Claims

1. An integrated circuit for driving the transistor of a power supply circuit that includes a transformer with a primary coil, a secondary coil and an auxiliary coil, and a transistor that controls the current flowing through the primary coil, and generates an output voltage of a predetermined level for a load from an input voltage, A first comparison circuit compares a first voltage corresponding to the voltage on the high-potential side of the transistor with a second voltage. An oscillator circuit that outputs an oscillation signal, A switching control circuit for controlling the switching of the transistor, Equipped with, The aforementioned switching control circuit is When the transistor is off, the current in the secondary coil is zero, which is a discontinuous mode. An on-signal output circuit outputs an on-signal to turn on the transistor after the oscillation signal is input and the first number of times the first voltage becomes the second voltage has reached a reference number of times. An off-signal output circuit that outputs an off-signal to turn off the transistor based on the current flowing through the transistor, A first holding circuit that holds the aforementioned reference number of times, An adjustment circuit that increases the reference number of cycles under the first condition when the load current flowing through the load decreases, and decreases the reference number of cycles under the second condition, which is more stringent than the first condition, when the load current increases. An integrated circuit that includes [this component].

2. The integrated circuit according to claim 1, A counter that counts the first number of times based on the comparison result of the first comparison circuit, A second holding circuit that holds the first count when the oscillation signal is input as the second count, Equipped with, The first condition is that the first number of times is greater than the reference number of times. The second condition is that the state in which the second count is smaller than the reference count continues for a predetermined number of times. Integrated circuit.

3. The integrated circuit according to claim 2, The aforementioned ON signal output circuit is A mode determination circuit that determines whether the current in the secondary coil is not zero when the transistor is off, or whether it is in a continuous mode or a discontinuous mode. Includes, The adjustment circuit described above is A second comparison circuit compares the first number of times with the reference number of times. Includes, The aforementioned ON signal output circuit is In the discontinuous mode, the ON signal is output based on the oscillation signal and the comparison result of the second comparison circuit. An integrated circuit that includes [this component].

4. The integrated circuit according to claim 3, The adjustment circuit described above is A third comparison circuit compares the second number of times with the reference number of times, An update circuit updates the reference number based on the comparison result of the second comparison circuit and the comparison result of the third comparison circuit, An integrated circuit that includes [this component].

5. The integrated circuit according to claim 4, When the discontinuous mode is in operation, the ON signal output circuit outputs the ON signal based on the oscillation signal, the comparison result of the second comparison circuit, and the comparison result of the third comparison circuit. Integrated circuit.

6. An integrated circuit according to any one of claims 1 to 5, The aforementioned oscillator circuit is If the ON signal is input within a period corresponding to the frequency of the oscillation signal after the oscillation signal is output, the oscillation signal is output at the time when the ON signal has been input and the period has elapsed. Integrated circuit.

7. An integrated circuit according to any one of claims 1 to 5, The aforementioned oscillator circuit is A first timing circuit that starts timing based on the oscillation signal or the ON signal, When the first timing circuit has timed a period corresponding to the frequency of the oscillation signal, an oscillation signal output circuit outputs the oscillation signal, An integrated circuit that includes [this component].

8. An integrated circuit according to any one of claims 1 to 7, The aforementioned ON signal output circuit is After the first voltage becomes the second voltage and a first period has elapsed, the system includes a first timer that outputs the ON signal, Integrated circuit.

9. An integrated circuit according to any one of claims 1 to 8, The aforementioned ON signal output circuit is A measurement circuit for measuring the period during which the first voltage becomes the second voltage, After the first voltage becomes the second voltage, and after a second period corresponding to the measured period has elapsed, a second timer outputs the ON signal. An integrated circuit that includes [this component].

10. A power supply circuit that generates an output voltage of a predetermined level for a load from an input voltage, A transformer including a primary coil, a secondary coil and an auxiliary coil, and a transistor that controls the current flowing through the primary coil, An integrated circuit that drives the aforementioned transistor, Equipped with, The aforementioned integrated circuit is A first comparison circuit compares a first voltage corresponding to the voltage on the high-potential side of the transistor with a second voltage. An oscillator circuit that outputs an oscillation signal, A switching control circuit for controlling the switching of the transistor, Equipped with, The aforementioned switching control circuit is When the transistor is off, the current in the secondary coil is zero, which is a discontinuous mode. An on-signal output circuit outputs an on-signal to turn on the transistor after the oscillation signal is input and the first number of times the first voltage becomes the second voltage has reached a reference number of times. An off-signal output circuit that outputs an off-signal to turn off the transistor based on the current flowing through the transistor, A first holding circuit that holds the aforementioned reference number of times, An adjustment circuit that increases the reference number of cycles under the first condition when the load current flowing through the load decreases, and decreases the reference number of cycles under the second condition, which is more stringent than the first condition, when the load current increases. A power supply circuit including this.

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