DC-DC converter and control circuit thereof
The present invention is intended to provide a DC-DC converter, in which the relationship between the duty ratio of a drive signal and the output DC voltage is nonlinear, being characterized in that the relationship between an error signal and the output DC voltage is linear, and that the design of stabilizing the feedback system is facilitated. The DC-DC converter comprises an error-amplifier circuit for generating the error signal that is obtained by amplifying the error between the output and a target value, an oscillating circuit for generating a triangular wave signal having an amplitude corresponding to the error signal, and a comparison circuit for comparing the triangular wave signal with a reference signal having a predetermined value and for generating the drive signal to turn ON/OFF a switching device.
1. A DC-DC converter having a switching device that is turned ON and OFF repeatedly, and an inductor that stores energy from the input during the ON period of said switching device and releases the energy to the output during the OFF period of said switching device, comprising:
an error-amplifier circuit for generating an error signal that is obtained by amplifying the error between the output and a target value,
an oscillating circuit for generating a triangular wave signal having an amplitude corresponding to said error signal, and
a comparison circuit for comparing said triangular wave signal with a reference signal having a predetermined value and for generating a drive signal to turn ON/OFF said switching device.
2. The DC-DC converter according to claim 1 , wherein said oscillating circuit generates a triangular wave signal having an amplitude being proportionate to the magnitude of said error signal.
3. The DC-DC converter according to claim 2 , wherein said oscillating circuit comprises:
a current source circuit for outputting a current being proportionate to the magnitude of said error signal,
a clock signal generator for generating a clock signal having a predetermined frequency,
a discharge switch that is turned ON and OFF according to said clock signal, and
a capacitor that is charged using said current source circuit and discharged using said discharge switch; and
said triangular wave signal has the waveform of the charging/discharging voltage of said capacitor.
4. The DC-DC converter according to claim 1 , wherein said comparison circuit compares said triangular wave signal with a reference signal having a magnitude corresponding to the input voltage.
5. The DC-DC converter according to claim 1 , wherein said comparison circuit compares said triangular wave signal with a reference signal having a magnitude that decreases from a level higher than said predetermined value at the time of startup to said predetermined value with the passage of time.
6. The control circuit of a DC-DC converter, having a switching device that is turned ON and OFF repeatedly, and an inductor that stores energy from the input during the ON period of said switching device and releases the energy to the output during the OFF period of said switching device, comprising:
an error-amplifier circuit for generating an error signal that is obtained by amplifying the error between the output and a target value,
an oscillating circuit for generating a triangular wave signal having an amplitude corresponding to said error signal, and
a comparison circuit for comparing said triangular wave signal with a reference signal having a predetermined value and for generating a drive signal to turn ON/OFF said switching device.
7. The control circuit of the DC-DC converter according to claim 6 , wherein said oscillating circuit generates a triangular wave signal having an amplitude being proportionate to the magnitude of said error signal.
8. The control circuit of the DC-DC converter according to claim 7 , wherein
said oscillating circuit comprises:
a current source circuit for outputting a current being proportionate to the magnitude of said error signal,
a clock signal generator for generating a clock signal having a predetermined frequency,
a discharge switch that is turned ON and OFF according to said clock signal, and
a capacitor that is charged using said current source circuit and discharged using said discharge switch; and
said triangular wave signal has the waveform of the charging/discharging voltage of said capacitor.
9. The control circuit of the DC-DC converter according to claim 6 , wherein said comparison circuit compares said triangular wave signal with a reference signal having a magnitude corresponding to the input voltage.
10. The control circuit of the DC-DC converter according to claim 6 , wherein said comparison circuit compares said triangular wave signal with a reference signal having a magnitude that decreases from a level higher than said predetermined value at the time of startup to said predetermined value with the passage of time.