Claims
- 1. A discharge lamp ballast circuit having a DC/DC converter circuit that has a switching device for switching a primary current on a fly-back transformer, comprising:
a snubber circuit for the switching device; a capacitor connected in parallel with the switching device or the fly-back transformer and is capable of generating a resonance with a leakage reactor of the fly-back transformer; and a control circuit which drives the switching device in a PFM manner, and is capable of performing a non-zero voltage switching or non-zero current switching during a lighting preparation period of the discharge lamp and performing a zero voltage switching or zero current switching after the lighting preparation period.
- 2. The discharge lamp ballast circuit according to claim 1, wherein the capacitor is connected in parallel with the switching device, and the control circuit is capable of performing the non-zero voltage switching and the zero voltage switching.
- 3. The discharge lamp ballast circuit according to claim 1, wherein the capacitor is connected in parallel with the primary coil of the fly-back transformer, and the control circuit is capable of performing the non-zero voltage switching and the zero voltage switching.
- 4. The discharge lamp ballast circuit according to claim 1, wherein the control circuit drives the switching device so that the switching device switches after the voltage on the primary coil reaches to a peak value for performing the non-zero voltage switching.
- 5. The discharge lamp ballast circuit according to claim 1, wherein an inductance of the leakage reactor of the fly-back transformer and a capacitance of the capacitor are set so that a condition for enabling the zero voltage switching and for setting the switching frequency in the PFM control into the predetermined value is satisfied, and so that the inductance of the leakage reactor is minimized under satisfying the condition.
- 6 The discharge lamp ballast circuit according to claim 1, wherein the control circuit drives the switching device by a switching frequency when performing the zero voltage switching, and drives the switching device by a higher switching frequency when performing the non-zero voltage switching in comparison with the switching frequency in the zero voltage switching, the higher switching frequency is obtained by shortening an off period of the switching device, and the off period is shortened by turning on the switching device after a voltage on the primary coil reaches to a peak value and before the voltage on the primary coil reaches to zero or below zero.
- 7. The discharge lamp ballast circuit according to claim 1, wherein the control circuit extends an off period of the switching device when an instantaneous lamp power drop is detected based on a signal corresponding to the lamp power to enable the zero voltage switching.
- 8. The discharge lamp ballast circuit according to claim 1, further comprising a rectifier diode connected to the secondary coil, wherein the capacitor is connected between a connection point between the secondary coil and the diode and a ground of the circuit, and the control circuit is capable of performing the non-zero current switching and the zero current switching.
- 9. The discharge lamp ballast circuit according to claim 8, wherein the control circuit drives the switching device so that the switching device switches after the current on the primary coil reaches to a peak value for performing the non-zero current switching.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2001-249343 |
Aug 2001 |
JP |
|
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on Japanese Patent Application No. 2001-249343 filed on Aug. 20, 2001 the contents of which are incorporated herein by reference.