Discharge lamp ballast circuit having snubber circuit

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 one of the switching device and the fly-back transformer for generating a resonance with a leakage reactor of the fly-back transformer;
• and
• a control circuit for driving the switching device in a PFM manner, for performing one of a non-zero voltage switching and a non-zero current switching during a lighting preparation period of the discharge lamp, and for performing one of a zero voltage switching and a zero current switching after the lighting preparation period,
• 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 upon the condition being satisfied.

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 one of the switching device and the fly-back transformer for generating a resonance with a leakage reactor of the fly-back transformer;
• and
• a control circuit for driving the switching device in a PFM manner, for performing one of a non-zero voltage switching and a non-zero current switching during a lighting preparation period of the discharge lamp, and for performing one of a zero voltage switching and a zero current switching after the lighting preparation period,
• 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 a primary coil of the fly-back transformer reaches to a peak value and before the voltage on the primary coil reaches to zero or below zero.

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 one of the switching device and the fly-back transformer for generating a resonance with a leakage reactor of the fly-back transformer;
• and
• a control circuit for driving the switching device in a PFM manner, for performing one of a non-zero voltage switching and anon-zero current switching during a lighting preparation period of the discharge lamp, and for performing one of a zero voltage switching and a zero current switching after the lighting preparation period,
• 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.

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 one of the switching device and the fly-back transformer for generating a resonance with a leakage reactor of the fly-back transformer;
• and
• a control circuit for driving the switching device in a PFM manner, for performing one of a non-zero voltage switching and a non-zero current switching during a lighting preparation period of the discharge lamp, and for performing one of a zero voltage switching and a zero current switching after the lighting preparation period,
• a rectifier diode connected to the a secondary coil of the fly-back transformer, 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 performs the non-zero current switching and the zero current switching.

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 between a terminal of the switching device and a terminal of the fly-back transformer for generating a resonance with a leakage reactor of the fly-back transformer;
• and
• a control circuit for driving the switching device in a PFM manner, performing one of a non-zero voltage switching and a non-zero current switching during a lighting preparation period of the discharge lamp, and for performing one of a zero voltage switching and a zero current switching after the lighting preparation period,
• wherein the control circuit drives the switching device so that the switching device switches after the voltage on the primary coil reaches a peak value for performing the non-zero voltage switching.