Low-voltage power supply circuit for illumination, illumination device, and low-voltage power supply output method for illumination
In a low-voltage power supply circuit for illumination that rectifies an ac power supply by means of a rectifier circuit, that controls this rectified output by means of a power-factor control circuit, and that supplies a low-voltage power supply for illumination, the power-factor control circuit is composed of a step-down circuit and is further provided with a current-limiting capability.
1. A low-voltage power supply circuit for supplying a low-voltage power supply for illumination, comprising:
a rectifier circuit for rectifying an ac power supply;
a power-factor control circuit for controlling rectified output from said rectifier circuit, said power-factor control circuit being composed of a step-down circuit, and moreover, being provided with a current-limiting capability,
a switch element that is both driven by the output of said rectifier circuit and the detected output of a power supply current and switched by the control output from said power-factor control circuit;
a step-down transformer that is controlled by the output of said switch element;
a output circuit for both rectifying the output of said transformer and filtering the high-frequency component by means of a passive element; and
a current detection circuit for obtaining the detected output of said power supply current from the output current of said simplified output circuit.
2. A low-voltage power supply circuit for illumination according to claim 1 , wherein:
one of the input terminals of said transformer is connected to the output of said switch element, and the other input terminal is connected to the output of said rectifier circuit.
3. A low-voltage power supply circuit for illumination according to claim 1 , wherein said power-factor control circuit:
compares the detected output of a load current with a prescribed reference value and amplifies the error;
multiplies this amplified output with the output of said rectifier circuit;
compares this multiplied output with a prescribed high-frequency signal; and
drives a switch element by means of this comparison output.
4. A low-voltage power supply circuit for illumination according to claim 2 , wherein said power-factor control circuit:
compares the detected output of a load current with a prescribed reference value and amplifies the error;
multiplies this amplified output with the output of said rectifier circuit;
compares this multiplied output with a prescribed high-frequency signal; and
drives a switch element by means of this comparison output.
5. A low-voltage power supply circuit for illumination according to claim 3 , wherein said prescribed high-frequency signal is composed of a sawtooth-wave signal of 20-200 kHz.
6. A low-voltage power supply circuit for illumination according to claim 4 , wherein said prescribed high-frequency signal is composed of a sawtooth-wave signal of 20-200 kHz.
7. An illumination device that uses the low-voltage power supply circuit for illumination according to claim 1 that is connected to a light source for illumination.
8. An illumination device according to claim 7 , wherein said light source for illumination is a dc-lighted light source such as an organic EL or an LED.