Switching control circuit and power supply circuit
A switching control circuit including: a command value output circuit that respectively outputs a command value indicating a first time period, and command values indicating second and third time periods, in first and second load states; a first driver circuit that, in the first load state, turns on a first transistor after a first inductor current reaches a first value, and subsequently turns off the first transistor when the first time period has elapsed; and a second driver circuit that, in the second load state, turns on a second transistor when a second inductor current reaches a second value, and subsequently turns off the second transistor when the third time period has elapsed. The first driver circuit, in the second load state, turns on the first transistor when the first inductor current reaches the first value, and subsequently turns off the first transistor when the second time period has elapsed.
1 . A switching control circuit for a power supply circuit that generates an output voltage at a target level from an alternating current (AC) voltage inputted thereto, the power supply circuit including
a first inductor and a second inductor, the first and second inductors being configured to receive a voltage corresponding to the AC voltage,
a first transistor configured to control a first inductor current flowing through the first inductor, and
a second transistor configured to control a second inductor current flowing through the second inductor,
the switching control circuit being configured to control switching of the first transistor and the second transistor, the switching control circuit comprising:
a command value output circuit configured to,
when a current value of a load current flowing through a load of the power supply circuit is smaller than a first predetermined value and the load is in a first state, output a first command value indicating a first time period corresponding to the output voltage, and
when the current value of the load current is larger than a second predetermined value and the load is in a second state, output
a second command value indicating a second time period corresponding to the output voltage, and
a third command value indicating a third time period;
a first driver circuit configured to, when the load is in the first state,
receive the first command value,
turn on the first transistor, after the first inductor current reaches a first value, and
turn off the first transistor, in response to the first time period based on the first command value having elapsed since the first transistor is turned on; and
a second driver circuit configured to, when the load is in the second state,
receive the third command value,
turn on the second transistor, in response to the second inductor current reaching a second value, and
turn off the second transistor, in response to the third time period based on the third command value having elapsed since the second transistor is turned on, wherein
the first driver circuit is further configured to, when the load is in the second state,
receive the second command value,
turn on the first transistor, in response to the first inductor current reaching the first value, and
turn off the first transistor, in response to the second time period based on the second command value having elapsed since the first transistor is turned on.
2 . The switching control circuit according to claim 1 , wherein each of the second time period and the third time period is shorter than the first time period at a time before a state of the load changes to the second state.
3 . The switching control circuit according to claim 2 , further comprising
a timer circuit configured to measure a switching period of the first transistor, wherein
the second driver circuit is further configured to turn on the second transistor, in response to
the state of the load changing to the second state,
a time period corresponding to a quarter of the switching period of the first transistor having elapsed, and
a first condition that the second inductor current reaches the second value being satisfied.
4 . The switching control circuit according to claim 3 , wherein the second driver circuit is further configured to turn on the second transistor, in response to
a time period corresponding to a half of the switching period of the first transistor having elapsed after the first condition is satisfied, and
a second condition that the second inductor current reaches the second value being satisfied.
5 . The switching control circuit according to claim 1 , wherein each of the second time period and the third time period is equal to a half of the first time period at a time before a state of the load changes to the second state.
6 . The switching control circuit according to claim 1 , further comprising
an error output circuit configured to output an error between a predetermined ratio and a ratio between a switching period of the first transistor and a time difference between a first timing at which the first inductor current reaches the first value and a second timing at which the second inductor current reaches the second value, wherein
the second driver circuit is further configured to, when the load is in the second state,
turn on the second transistor, after the second inductor current reaches the second value, and
turn off the second transistor, in response to a fourth time period according to the error and the third command value having elapsed.
7 . The switching control circuit according to claim 1 , wherein
the power supply circuit further includes a first load detection circuit configured to detect a state of the load, and
the command value output circuit outputs the first command value or the second and third command values, based on a result of detection of the first load detection circuit and the first command value indicating the first time period.
8 . The switching control circuit according to claim 1 , further comprising
a second load detection circuit configured to detect a state of the load, based on the first command value indicating the first time period, wherein
the command value output circuit outputs the first command value or the second and third command values, based on a result of detection of the second load detection circuit and the first command value indicating the first time period.
9 . A power supply circuit configured to generate an output voltage at a target level from an alternating current (AC) voltage inputted thereto, the power supply circuit comprising:
a first inductor and a second conductor, the first and second inductors being configured to receive a voltage corresponding to the AC voltage;
a first transistor configured to control a first inductor current flowing through the first inductor;
a second transistor configured to control a second inductor current flowing through the second inductor;
a switching control circuit configured to control switching of the first transistor and the second transistor, the switching control circuit including
a command value output circuit configured to,
when a current value of a load current flowing through a load of the power supply circuit is smaller than a first predetermined value and the load is in a first state, output a first command value indicating a first time period corresponding to the output voltage, and
when the current value of the load current is larger than a second predetermined value and the load is in a second state, output
a second command value indicating a second time period corresponding to the output voltage, and
a third command value indicating a third time period;
a first driver circuit configured to, when the load is in the first state,
receive the first command value,
turn on the first transistor, in response to the first inductor current reaching a first value, and
turn off the first transistor, in response to the first time period based on the first command value having elapse since the first transistor is turned on; and
a second driver circuit configured to, when the load is in the second state,
receive the third command value,
turn on the second transistor, after the second inductor current reaches a second value, and
turn off the second transistor, in response to the third time period based on the third command value having elapsed since the second transistor is turned on, wherein
the first driver circuit is further configured to, when the load is in the second state,
receive the second command value,
turn on the first transistor, in response to the first inductor current reaching the first value, and
turn off the first transistor, in response to the second time period based on the second command value having elapsed since the first transistor is turned on.