Current-controlled DC-DC converter control circuit, current-controlled DC-DC converter, and method for controlling current-controlled DC-DC converter
The invention includes a flip-flop circuit that controls a main switching element of a DC-DC converter by switching and an oscillation circuit that is connected to a set terminal of the flip-flop circuit and outputs an oscillation signal that gradually increases and decreases in oscillation frequency in accordance with an increase and decrease in output voltage value of the DC-DC converter when the DC-DC converter is in a transition state between a stop state and a steady operation state. In a process that the output voltage gradually rises and gradually falls, the oscillation frequency of the oscillation signal gradually rises and gradually falls, a time interval at which the main switching element is set into a conductive state is extended. No excess electric power is supplied to the output voltage, and the output voltage can be made to have a smooth ramp waveform.
1. A current-controlled DC-DC converter control circuit comprising an oscillation circuit that instructs on timing of periodic switching control of a DC-DC converter, wherein
when the switching control is in a transition state between a stop state and a steady operation state, the oscillation circuit gradually increases oscillation frequency in a transition state where an output voltage value of the DC-DC converter rises with elapse of time and gradually decreases oscillation frequency in a transition state where an output voltage value of the DC-DC converter falls with elapse of time.
2. The current-controlled DC-DC converter control circuit according to claim 1 , comprising a flip-flop circuit that controls main switching element of the DC-DC converter by switching, wherein
an oscillation signal outputted from the oscillation circuit is inputted into a set terminal of the flip-flop circuit.
3. The current-controlled DC-DC converter control circuit according to claim 1 , comprising a control terminal into which a voltage signal by which terminal voltage gradually rises according to a start instruction and the terminal voltage gradually falls according to a stop instruction is inputted, and
a frequency setting section that sets an oscillation frequency of the oscillation circuit according to the terminal voltage of the control terminal.
4. The current-controlled DC-DC converter control circuit according to claim 3 , comprising:
a first current section that outputs electric current to the control terminal;
a first switching circuit that establishes a current path to the circuit terminal via the first current section according to the start instruction;
a second current section that draws electric current from the control terminal; and
a second switching circuit that establishes a current path to the circuit terminal via the second current section according to the stop instruction.
5. The current-controlled DC-DC converter control circuit according to claim 4 , wherein any one of the first current section and the second current section or both comprise any one of a constant current circuit and a resistance element or both.
6. The current-controlled DC-DC converter control circuit according to claim 3 , wherein the frequency setting section comprises a buffer section that outputs a voltage according to the terminal voltage of the control terminal, and
a current setting section that sets a bias current according to the output voltage of the buffer section.
7. The current-controlled DC-DC converter control circuit according to claim 6 , wherein the buffer section comprises a first noninverting input terminal into which the terminal voltage of the control terminal is inputted, and
a second noninverting input terminal into which a steady setting voltage to set an oscillation frequency in the steady operation state is inputted, and
the buffer section outputs a lower voltage value of the voltages inputted into the first and second noninverting input terminals.
8. The current-controlled DC-DC converter control circuit according to claim 1 , wherein the oscillation circuit comprises a first capacitance element in which terminal voltage gradually rises by being gradually charged according to a start instruction and the terminal voltage gradually falls by being gradually discharged according to a stop instruction, and
a frequency setting section that sets an oscillation frequency according to the terminal voltage of the first capacitance element.
9. The current-controlled DC-DC converter control circuit according to claim 8 , comprising:
a charging current section that charges the first capacitance element;
a first switching circuit that establishes a charging path to the first capacitance element via the charging current section according to the start instruction;
a discharging current section that discharges the first capacitance element; and
a second switching circuit that establishes a discharging path from the first capacitance circuit via the discharging current section according to the stop instruction.
10. The current-controlled DC-DC converter control circuit according to claim 9 , wherein any one of the charging current section and the discharging current section or both comprise any one of a constant current circuit and a resistance element or both.
11. The current-controlled DC-DC converter control circuit according to claim 8 , wherein the frequency setting section comprises a buffer section that outputs a voltage according to the terminal voltage of the first capacitance element, and
a current setting section that sets a bias current according to the output voltage of the buffer section.
12. The current-controlled DC-DC converter control circuit according to claim 11 , wherein the buffer section comprises a first noninverting input terminal into which the terminal voltage of the first capacitance element is inputted, and
a second noninverting input terminal into which a steady setting voltage to set an oscillation frequency in the steady operation state is inputted, and
the buffer section outputs a lower voltage value of the voltages inputted into the first and second noninverting input terminals.
13. A current-controlled DC-DC converter comprising an oscillation circuit that instructs on timing of periodic switching control, wherein
when the switching control is in a transition state between a stop state and a steady operation state, the oscillation circuit gradually increases oscillation frequency in a transition state where an output voltage value of the DC-DC converter rises with elapse of time and gradually decreases oscillation frequency in a transition state where an output voltage value of the DC-DC converter falls with elapse of time.
14. The current-controlled DC-DC converter according to claim 13 , comprising:
a main switching element; and
a flip-flop circuit that controls the main switching element of the DC-DC converter by switching, wherein
an oscillation signal outputted from the oscillation circuit is inputted into a set terminal of the flip-flop circuit.
15. The current-controlled DC-DC converter according to claim 13 , wherein the oscillation circuit comprises a first capacitance element in which terminal voltage gradually rises by being gradually charged according to a start instruction and the terminal voltage gradually falls by being gradually discharged according to a stop instruction, and
a frequency setting section that sets an oscillation frequency of the oscillation circuit according to the terminal voltage of the control terminal.
16. The current-controlled DC-DC converter according to claim 13 , comprising:
a charging current section that charges the first capacitance element;
a first switching circuit that establishes a charging path to the first capacitance element via the charging current section according to the start instruction;
a discharging current section that discharges the first capacitance element; and
a second switching circuit that establishes a discharging path from the first capacitance element via the discharging current section according to the stop instruction.
17. The current-controlled DC-DC converter according to claim 16 , wherein any one of the charging current section and the discharging current section or both comprise any one of a constant current circuit and a resistance element or both.
18. The current-controlled DC-DC converter according to claim 15 , wherein the frequency setting section comprises a buffer section that outputs a voltage according to the terminal voltage of the first capacitance element, and
a current setting section that sets a bias current according to the output voltage of the buffer section.
19. The current-controlled DC-DC converter according to claim 18 , wherein the buffer section comprises a first noninverting input terminal into which the terminal voltage of the first capacitance element is inputted, and
a second noninverting input terminal into which a steady setting voltage to set an oscillation frequency in the steady operation state is inputted, and
the buffer section outputs a lower voltage value of the voltages inputted into the first and second noninverting input terminals.
20. A method for controlling a current-controlled DC-DC converter by which periodic switching control is carried out, comprising the steps of:
carrying out switching control with a first period in a steady operating state, and
when the switching control is in a transition state between a stop state and a steady operation state, gradually increasing oscillation period, with the first period as a shortest period, in a transition state where an output voltage value of the DC-DC converter rises with elapse of time, and gradually decreasing oscillation period, with the first period as a shortest period, in a transition state where an output voltage value of the DC-DC converter falls with elapse of time.