LED power supply device

Abstract

An LED power supply device disclosed in the present specification includes a DC dimmer circuit that performs dimming control of an LED such that the higher a reference voltage variably controlled according to a dimmer signal is, the smaller a current flowing in the LED is. This configuration makes it possible to achieve fine dimming control.

What is claimed is: 
     
       1. An LED power supply device comprising a DC dimmer circuit that performs dimming control of an LED such that the higher a reference voltage variably controlled according to a dimming signal is, the smaller an output current flowing in the LED is,
 wherein the DC dimmer circuit controls the output current such that a detection voltage having a voltage value that becomes higher according as the output current is smaller is equal to the reference voltage, 
 wherein the DC dimmer circuit includes:
 a current monitor that monitors the output current to generate a feedback signal; 
 a driver that performs constant current control of the output current according to the feedback signal; and 
 a microcomputer that generates the dimming signal, and 
 
 wherein the current monitor includes:
 a current DAC that converts the dimming signal which is PWM-driven into a dimming current having an analog value; 
 a detection voltage generation portion that generates the detection voltage according to the output current; 
 a reference voltage generation portion that generates the reference voltage according to the dimming current; and 
 an operational amplifier that generates the feedback signal in response to input of the detection voltage and the reference voltage thereto. 
 
 
     
     
       2. The LED power supply device of  claim 1 , wherein
 the detection voltage generation portion includes:
 a sense resistor provided on a path through which the output current flows; and 
 first and second resistors connected in series between an internal power supply terminal and a low-potential terminal of the sense resistor; and 
 
 the detection voltage is output from a connection node between the first and second resistors. 
 
     
     
       3. The LED power supply device of  claim 2 , wherein
 the reference voltage generation portion includes third and fourth resistors connected in series between the internal power supply terminal and a high-potential terminal of the sense resistor; and 
 a connection node between the third and fourth resistors is connected to an output terminal of the current DAC such that the reference voltage is output from the connection node. 
 
     
     
       4. An LED lighting apparatus, comprising:
 the LED power supply device of  claim 1 ; and 
 an LED that is driven by receiving power supply from the LED power supply device. 
 
     
     
       5. An LED power supply device comprising a DC dimmer circuit that performs dimming control of an LED such that the higher a reference voltage variably controlled according to a dimming signal is, the smaller an output current flowing in the LED is,
 wherein the DC dimmer circuit controls the output current such that a detection voltage having a voltage value that becomes higher according as the output current is smaller is equal to the reference voltage, 
 wherein the DC dimmer circuit includes:
 a current monitor that monitors the output current to generate a feedback signal; 
 a driver that performs constant current control of the output current according to the feedback signal; and 
 a microcomputer that generates the dimming signal, and 
 
 wherein the microcomputer generates the dimming signal by using a dimming table which defines correlation between dimming signal ratio and output current ratio. 
 
     
     
       6. The LED power supply device of  claim 5 , wherein
 the microcomputer detects, by using an initial version of the dimming table, a value of dimming signal ratio when output current ratio is zero, and corrects the dimming table such that the detected value of dimming signal ratio is equal to a target value. 
 
     
     
       7. An LED power supply device comprising a DC dimmer circuit that performs dimming control of an LED such that the higher a reference voltage variably controlled according to a dimming signal is, the smaller an output current flowing in the LED is,
 wherein the DC dimmer circuit controls the output current such that a detection voltage having a voltage value that becomes higher according as the output current is smaller is equal to the reference voltage, 
 wherein the DC dimmer circuit includes:
 a current monitor that monitors the output current to generate a feedback signal; 
 a driver that performs constant current control of the output current according to the feedback signal; and 
 a microcomputer that generates the dimming signal, and 
 
 wherein the LED power supply device is a fly-back power supply device that generates an output voltage from an input voltage, insulating a primary circuit system and a secondary circuit system from each other; and 
 the driver and the microcomputer are provided in the primary circuit system, and the current monitor is provided in the secondary circuit system. 
 
     
     
       8. The LED power supply device of  claim 7 , wherein the current monitor includes:
 a current DAC that converts the dimming signal which is PWM-driven into a dimming current having an analog value; 
 a detection voltage generation portion that generates the detection voltage according to the output current; 
 a reference voltage generation portion that generates the reference voltage according to the dimming current; and 
 an operational amplifier that generates the feedback signal in response to input of the detection voltage and the reference voltage thereto, and 
 wherein the current DAC includes: 
 a photo coupler that receives input of the dimming signal from the microcomputer; and 
 a capacitor that smooths output from the photo coupler to generate the dimming current.