Switching power source
View Patent ↗An error voltage Verr, as amplified by an amplifier, and an input voltage Vin, are multiplied together by a multiplier to generate a first threshold value signal Vth 1 , which is in phase with and similar in waveform to the input voltage Vin, and proportional in amplitude to the error voltage Verr. A second threshold value signal Vth 2 is generated from the first threshold value signal Vth 1 by a series circuit of a diode and a resistor. The power factor is increased by on/off-control of a switching element via a drive circuit, so that a current detection signal Vi, which is detected by a resistor and corresponds to an input current, falls between the two threshold value signals Vth 1 and Vth 2 . Since the off time is not fixed, the noise spectrum is spread and increase of the switching frequency is suppressed. Noise reduction thus can be attained.
1. A switching power source comprising:
a rectification circuit configured to produce a pulsating output by full-wave-rectifying an AC power source voltage;
a chopper circuit, including an inductor connected to the rectification circuit, a switching element that shunts when switched on, a current flowing through the inductor, and a capacitor configured to produce a DC output by smoothing a current supplied from the inductor;
a first signal generator configured to generate a first threshold value signal that is in phase with, and similar in waveform to, an input voltage of the chopper circuit, and is proportional in amplitude to an error of an output voltage of the chopper circuit;
a second signal generator configured to generate a second threshold value signal approximately proportional in amplitude to the first threshold value signal;
a current detector configured to detect the current flowing through the inductor; and
a switching control configured to turn off the switching element when a current detection value of the current detector reaches a level of the first threshold value signal, and to turn on the switching element when the current detection value becomes lower than a level of the second threshold value signal.
2. The switching power source according to claim 1 , wherein the second signal generator is a series circuit of a diode and a first resistor to which the first threshold value signal and a reference potential are applied respectively, or a series circuit of a first resistor and a parallel circuit of a diode and another resistor, the first threshold value signal and the reference potential being applied to the first resistor and the parallel circuit, respectively, and an output at a connecting point of the first resistor and the diode or the parallel circuit serves as the second threshold value signal.
3. The switching power source according to claim 1 , wherein the second signal generator is a series circuit of a resistor and a variable resistor to which the first threshold value signal and a reference potential are applied, respectively, and an output at a connecting point of the resistor and the variable resistor serves as the second threshold value signal.
4. The switching power source according to claim 3 , wherein the variable resistor comprises at least one series circuit of a resistor and a transistor, and the transistor is driven by at least one of the input voltage, the current flowing through the inductor, and the output voltage error.
5. The switching power source according to claim 3 , wherein the variable resistor comprises at least one series circuit of a resistor and a switch or a parallel circuit of plural series circuits of a resistor and a switch, and the switch is turned on and off by at least one of the input voltage, the current flowing through the inductor, and the output voltage error.
6. A switching power source comprising:
a rectification circuit configured to produce a pulsating output by full-wave-rectifying an AC power source voltage;
a chopper circuit including an inductor connected to the rectification circuit, a switching element that shunts, when switched on, a current flowing through the inductor, and a capacitor configured to produce a DC output by smoothing a current supplied from the inductor;
a first signal generator configured to generate a first threshold value signal which is in phase with, and similar in waveform to, an input voltage of the chopper circuit and is proportional in amplitude to an error of an output voltage of the chopper circuit;
a second signal generator configured to generate a second threshold value signal that is proportional to the first threshold value signal;
a modulator configured to modulate the second threshold value signal;
a current detector configured to detect the current flowing through the inductor; and
a switching control configured to turn off the switching element when a current detection value of the current detector reaches a level of the first threshold value signal, and to turn on the switching element when the current detection value becomes lower than a level of the second threshold voltage signal.
7. The switching power source according to claim 6 , wherein the second signal generator is a series circuit of a first resistor and a second resistor to which the first threshold value signal and a reference potential are applied respectively, and an output at a connecting point of the first resistor and the second resistor serves as the second threshold value signal.
8. The switching power source according to claim 6 , wherein the modulator comprises a transistor, to which the second threshold value signal and a reference potential are applied, and a drive circuit configured to drive the transistor on the basis of the first threshold value signal.
9. The switching power source according to claim 6 , wherein the modulator comprises a transistor, to which the second threshold value signal and a reference potential are applied, and a drive circuit configured to drive the transistor on the basis of a difference between the first threshold value signal and the second threshold value signal.
10. The switching power source according to claim 6 , wherein the modulator comprises a transistor, to which the second threshold value signal and a reference potential are applied, and a drive circuit configured to drive the transistor on the basis of a difference between the first threshold value signal and a control signal.