Lighting power supply device

Abstract

A lighting power supply device includes a control circuit controlling a transistor that controls a drive current flown through a lamp, receiving a pulsating flow converted from an alternating current by a rectifying circuit rectifying the alternating current subjected to phase control by a phase-controlled dimmer, and generating/outputting direct current voltage/current supplied to the lamp. The control circuit includes a time-voltage conversion circuit converting a time decided according to a phase of a voltage corresponding to the pulsating flow into a voltage; and a terminal to which a capacitor with an arbitrary capacitance value is connectable. The time-voltage conversion circuit allows the capacitor to generate a charging voltage corresponding to the phase of the pulsating flow. A sample-and-hold circuit takes in the charging voltage of the capacitor at predetermined timing corresponding to a change of an output of a voltage comparison circuit, and holds/outputs the taken-in voltage until next timing.

What is claimed is: 
     
       1. A lighting power supply device that receives a pulsating flow converted from an alternating current by a rectifying circuit that rectifies the alternating current subjected to phase control by a phase-controlled dimmer, and generates and outputs direct current voltage/current to be supplied to a lamp, the lighting power supply device comprising:
 a transistor that flows the current for turning on the lamp; and 
 a control circuit that receives a voltage corresponding to the current for the lamp as an input and controls the transistor, 
 wherein the control circuit includes:
 a time-voltage conversion circuit that converts a time decided by a phase of the pulsating flow into a voltage, and 
 a terminal to which a capacitor having an arbitrary capacitance value is connectable; 
 
 wherein the time-voltage conversion circuit includes:
 a current source capable of charging or discharging the capacitor with a predetermined current; 
 a switching unit capable of switching the charging and the discharging of the capacitor; 
 a sample-and-hold circuit capable of taking in and holding a charging voltage of the capacitor; 
 a voltage comparison circuit that compares an input voltage corresponding to the pulsating flow and a predetermined reference voltage with each other; and 
 a timing generation circuit to generate, based on an output of the voltage comparison circuit, a first timing signal which rises to a high level only for a time corresponding to an effective period of the input voltage, a second timing signal which is a one-shot pulse synchronized with a fall of the first timing signal, and a third timing signal which rises at a timing of a fall of the second timing signal and falls at a timing of a rise of the first timing signal, 
 
 wherein the time-voltage conversion circuit is configured to make the capacitor generate a charging voltage corresponding to the phase of the pulsating flow, and 
 wherein the sample-and-hold circuit is configured to take in the charging voltage at a predetermined timing corresponding to a change of an output of the voltage comparison circuit, and to hold and output the taken-in voltage until a next timing. 
 
     
     
       2. The lighting power supply device according to  claim 1 , wherein the control circuit is configured as a semiconductor integrated circuit, the terminal is provided as an external terminal of the semiconductor integrated circuit, and the capacitor is configured as an external element to be connected to the external terminal. 
     
     
       3. The lighting power supply device according to  claim 1 , wherein the time-voltage conversion circuit further comprises, between the external terminal and the sample-and-hold circuit, a voltage buffer that performs impedance conversion for the charging voltage of the capacitor and transmits the charging voltage to the sample-and-hold circuit. 
     
     
       4. The lighting power supply device according to  claim 1 , wherein:
 the current source is turned on according to the fist timing signal to make the capacitor charge with the predetermined current; 
 the sample-and-hold circuit takes in a charging voltage of the capacitor according to the second timing signal, and holds the taken-in voltage until a next timing to output the voltage; and 
 the switching unit is turned on according to the third timing signal to make the capacitor discharge.