Discharge Lamp Lighting Circuit

• US 20080018263A1
• Filed: 07/19/2007
• Published: 01/24/2008
• Est. Priority Date: 07/20/2006
• Status: Active Grant

• Current Assignee: Koito Manufacturing Company Limited
• Original Assignee: Koito Manufacturing Company Limited
• Inventors: Ichikawa, Tomoyuki, Ohta, Shinji
• Granted Patent: US 7,557,513 B2
• Time in Patent Office: Days
• US Class Current: 315/274
• CPC Class Codes: H05B 41/288 with semiconductor devices and specially adapted for lamps without preheating electrodes, e.g. for high-intensity discharge lamps, high-pressure mercury or sodium lamps or low-pressure sodium lamps H05B41/2806 takes precedence

Abstract

A lighting circuit includes a capacitor and inductor for a resonance, and a first output, a second output, a resistor and a monitor circuit. A DC-AC converting circuit generates an AC voltage from a DC voltage. The resistor has an end connected to the second output and the other end connected to an end of a secondary winding. A monitoring output is connected to the other end of the resistor, and is provided for providing a signal for monitoring a current flowing to a discharge lamp. The end of the resistor is connected to a grounding conductor GND. The monitor circuit receives a signal from the monitoring output. The monitor circuit generates a signal for monitoring a current IL flowing to the discharge lamp.

Claims

1. A lighting circuit for turning on a discharge lamp, comprising:

a DC-AC converting circuit to convert an input DC voltage into an AC voltage in response to a control signal for controlling power to be applied to the discharge lamp;

a transformer including a primary winding and a secondary winding to receive the AC voltage from output of the DC-AC converting circuit;

a capacitor on the primary side of the transformer;

an inductor on the primary side of the transformer;

first and second outputs for supplying a power from the secondary winding to the discharge lamp;

a resistor having one end connected to the second output and grounded and the other end connected to one end of the secondary winding; and

a detecting circuit including a current monitor circuit for monitoring a current flowing to the discharge lamp by using a signal sent from the other end of the resistor,

wherein the capacitor, the inductor and the primary winding are connected in series.

2. The lighting circuit according to claim 1, wherein the secondary winding of the transformer has an intermediate tap,

the detecting circuit has a first generating circuit having an input connected to the other end of the resistor and a voltage monitor circuit,

the first generating circuit is operable to generate a first signal corresponding to an amplitude of the AC voltage at the input, and

the voltage monitor circuit includes:

a second generating circuit having an input connected to the intermediate tap and operable to generate a second signal corresponding to the amplitude of the AC voltage at the input; and

a first arithmetic circuit for calculating the first signal and the second signal to output a lamp voltage equivalent signal.

3. The lighting circuit according to claim 1, wherein the secondary winding of the transformer has an intermediate tap,

the detecting circuit has a first generating circuit having an input connected to the other end of the resistor and a voltage monitor circuit,

the first generating circuit is operable to generate a first signal corresponding to an amplitude of the AC voltage at the input, and

the voltage monitor circuit includes:

a third generating circuit having a first input connected to the other end of the resistor and a second input connected to the intermediate tap of the secondary winding, and operable to generate a third signal corresponding to a difference between AC signals sent from the first and second inputs; and

a second arithmetic circuit for calculating the first signal and the third signal to output a lamp voltage equivalent signal.

4. The lighting circuit according to claim 1, wherein the secondary side of the transformer has an additional winding,

the detecting circuit includes a first generating circuit having an input connected to the other end of the resistor and a voltage monitor circuit,

the first generating circuit generates a first signal corresponding to an amplitude of the AC voltage at the input, and

the voltage monitor circuit includes:

a fourth generating circuit having an input connected to the additional winding and operable to generate a fourth signal depending on an amplitude of an AC voltage corresponding to a potential difference between both ends of the additional winding; and

a third arithmetic circuit for calculating the first signal and the fourth signal to output a lamp voltage equivalent signal.

5. The lighting circuit according to claim 2, wherein the first generating circuit includes a holding circuit to hold and output a signal corresponding to an amplitude of a signal sent from the input of the first generating circuit.

6. The lighting circuit according to claim 3, wherein the first generating circuit includes a holding circuit to hold and output a signal corresponding to an amplitude of a signal sent from the input of the first generating circuit.

7. The lighting circuit according to claim 4, wherein the first generating circuit includes a holding circuit to hold and output a signal corresponding to an amplitude of a signal sent from the input of the first generating circuit.