DC-DC converter, power supply system, and power supply method
According to an embodiment, a DC-DC converter comprises: an error amplifier that receives a soft start signal and amplifies a difference between an output voltage signal and a reference voltage signal; a PWM control circuit that controls ON and OFF states of a first switching transistor and a second switching transistor based on the output of the error amplifier; a frequency divider that divides a frequency signal and outputting a divided frequency signal; an accumulator that performs an adding operation based on the divided frequency signal and a control signal; and a DA converter that generates the soft start signal based on an output of the accumulator.
1. A DC-DC converter comprising:
an error amplifier that receives a soft start signal and amplifies a difference between an output voltage signal and a reference voltage signal;
a PWM control circuit that controls ON and OFF states of a first switching transistor and a second switching transistor based on the output of the error amplifier;
a frequency divider that divides a frequency signal and outputs a divided frequency signal;
an accumulator that performs an adding operation based on the divided frequency signal and a control signal; and
a DA converter that generates the soft start signal based on an output of the accumulator.
2. The DC-DC converter according to claim 1 , wherein the accumulator controls a soft start time based on the control signal as an accumulated value.
3. The DC-DC converter according to claim 2 , wherein the accumulator shortens the soft start time when a value of the control signal increases.
4. The DC-DC converter according to claim 1 , wherein a soft start time is set with (Vref/(AN*Vdac))×N÷fosc, and wherein Vref is a reference voltage, AN is a control signal, Vdac is a DA converter resolution, N is a frequency division ratio, and fosc is a frequency signal.
5. The DC-DC converter according to claim 1 , wherein the accumulator resets a soft start time based on a reset signal.
6. The DC-DC converter according to claim 1 , wherein the accumulator sets a signal outputted to the DA converter to a constant value when the soft start signal becomes a predetermined value.
7. The DC-DC converter according to claim 1 , wherein the error amplifier amplifies a difference between the output voltage signal and one of a group consisting of a signal at a low potential side of the soft signal and a reference voltage signal.
8. A power source supply system comprising:
a CPU; and
a DC-DC converter that includes an error amplifier that receives a soft start signal for soft start process and amplifies and outputs a difference between an output voltage signal and a reference voltage signal, and a PWM control circuit that controls ON and OFF states of a first switching transistor and a second switching transistor based on the output of the error amplifier,
wherein the DC-DC converter includes:
a frequency divider that divides a frequency signal and outputting a divided frequency signal,
an accumulator that performs an adding operation based on the divided frequency signal and a control signal, and
a DA converter that generates the soft start signal based on an output of the accumulator.
9. The power source supply system according to claim 8 , wherein the CPU supplies a reset signal, and the DC-DC converter resets the soft start process according to the reset signal.
10. The power source supply system according to claim 8 , wherein the CPU supplies a frequency division ratio signal, and the frequency divider divides the frequency signal according to the frequency division ratio signal.
11. A power source supply method comprising:
amplifying a difference between a reference voltage signal and an output voltage signal or a difference between the reference voltage signal and a signal at a low potential side of a soft start signal;
performing PWM control for ON and OFF states of a first switching transistor and a second switching transistor based on an output of the error amplifier;
outputting the output voltage signal;
dividing a frequency signal to output a divided frequency signal;
accumulating a set signal according to the divided frequency signal; and
generating the soft start signal according to result of the accumulation.
12. The power source supply method according to claim 11 , wherein a soft start time is shortened when a value of the set signal increases.
13. The power source supply method according to claim 11 , wherein soft start time is set with (Vref/(AN*Vdac))×N÷fosc, and wherein Vref is a reference voltage, AN is a control signal, Vdac is a DA converter resolution, N is a frequency division ratio, and fosc is a frequency signal.
14. A DC-DC converter comprising:
a first error amplifier that receives a signal for a first soft start and amplifies a difference between a first output voltage signal and a first reference voltage signal;
a second error amplifier that receives a signal for a second soft start and amplifies a difference between a second output voltage signal and a second reference voltage signal;
a first PWM control circuit that controls ON and OFF states of a first switching transistor and a second switching transistor based on an output of the first error amplifier;
a second PWM control circuit that controls ON and OFF states of a third switching transistor and a fourth switching transistor based on an output of the second error amplifier;
a frequency divider that divides a frequency signal and outputting a divided frequency signal;
a first accumulator that performs an adding operation based on the first divided frequency signal and a first control signal;
a second accumulator that performs an adding operation based on the second divided frequency signal and a second control signal;
a first DA converter that performs the first soft start signal based on an output of the first accumulator; and
a second DA converter that generates the second soft start signal based on an output of the second accumulator.
15. The DC-DC converter according to claim 14 , wherein the first accumulator controls a first soft start time based on the first control signal as an accumulated value, and the second accumulator controls a second soft start time based on the second control signal as an accumulated value.
16. The DC-DC converter according to claim 14 , wherein the first accumulator and the second accumulator shorten either the first soft start time or the second start time when a value of the first control signal or the second control signal increases.
17. The DC-DC converter according to claim 14 , wherein a soft start time is set with (Vref/(AN*Vdac))×N÷fosc, and wherein Vref is a reference voltage, AN is a control signal, Vdac is a DA converter resolution, N is a frequency division ratio, and fosc is a frequency signal.
18. The DC-DC converter according to claim 14 , wherein the first accumulator resets a first soft start according to a first reset signal, and the second accumulator resets a second soft start according to a second reset signal.
19. A power source supply system comprising:
a CPU;
a first error amplifier receives a signal for a first soft start and amplifiers a difference between a first output voltage signal and a second reference voltage signal;
a second error amplifier that includes receives a signal for a second soft start and amplifiers a difference between a second output voltage signal and a second reference voltage signal;
a first PWM control circuit that controls ON and OFF states of a first switching transistor and a second switching transistor based on an output of the first error amplifier;
a second PWM control circuit that controls ON and OFF states of a third switching transistor and a fourth switching transistor based on an output of the second error amplifier;
a frequency divider that divides a frequency signal and outputs a divided frequency signal;
a first accumulator that performs an adding operation based on the first divided frequency signal and a first control signal supplied from the CPU;
a second accumulator that performs an adding operation based on the second divided frequency signal and a second control signal supplied from the CPU;
a first DA converter that generates the first soft start signal based on an output of the first accumulator; and
a second DA converter that generates the second soft start signal based on an output of the second accumulator.
20. The power source supply system according to claim 19 , wherein the CPU supplies a frequency division ratio signal, and the frequency divider divides the frequency signal according to the frequency division ratio signal.