Electric lamp and discharge devices: systems – Surge generator or inductance in the supply circuit
Reexamination Certificate
1999-10-12
2001-02-13
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Surge generator or inductance in the supply circuit
C315S2090SC, C315S2090CD, C315S082000, C315SDIG005
Reexamination Certificate
active
06188180
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrical circuits for starting and restarting high intensity discharge (HID) lamps and, more particularly, to a novel circuit for producing high ignition voltage for starting an HID lamp.
2. Related Art
It is well known in the art that HID lamps commonly operate in a starting mode, an operating or steady state mode, and a restrike mode. During the starting mode, a relatively high value of starting voltage (i.e., ignition voltage) of about 25 KV is applied across electrodes of a lamp to first place the gases of the lamp into a suitable ionized condition for striking or initiating a glow breakdown state.
Automotive HID ballasts typically consist of a DC to DC converter, an H-bridge and an ignitor circuit, for example, see U.S. Pat. No. 4,904,907 to Allison.
Prior art ignitor circuits generally consist of a pulse transformer capable of producing a high voltage pulse and a drive circuit consisting of a capacitor, a spark gap and an resistor. For example, U.S. Pat. No. 5,036,256 to Garrison discloses an arc discharge ballast suitable for automotive applications consisting of a DC to DC converter, step-up transformer, rectifier and voltage doubler, energy storage circuit, and ignition transformer. In the Garrison circuit, a capacitor, resistor and spark gap form a relaxation oscillator capable of periodically pulsing the ignition transformer. The maximum charge voltage on the capacitor is limited to the supply voltage applied to the input of the relaxation oscillator.
In general, higher charge voltages are desirable since the energy stored in the capacitor is ½ CV
2
. Indeed, higher charge voltages permit a reduction in the capacitor size while maintaining a constant amount of stored energy. One method of increasing the charge voltage above a supply voltage is to use a voltage doubler operated from an H-bridge as described in U.S. Pat. No. 5,534,753 to Blom. In this way, charge voltages of up to twice the supply voltage may be obtained. In a voltage doubler, the effective capacitance is halved since there are two energy storage capacitors in series.
Unfortunately, the prior art arc discharge ballast circuits are disadvantageous for a number of reasons which include a limitation in the reduction of the energy storage capacitor, excessive voltage pulsing of the ignition transformer and asynchronous operation of the ignition pulse circuit with respect to the H-bridge circuit.
Accordingly, there is a need in the art for an improved ignition circuit for automotive HID lamps which permits doubling the pulse voltage, reducing the size of the energy storage capacitors by more than one half, synchronization of the ignition voltage pulse with the H-bridge circuit, and limiting the number of ignition pulses per half cycle of the H-bridge.
SUMMARY OF THE INVENTION
In order to overcome the deficiencies of the prior art, the ignition circuit for an HID lamp in accordance with the invention includes first and second series coupled switching transistors connected across upper and lower voltage buses to which a source of DC voltage is connectable, the first switching transistor being connected from the second switching transistor at a common node to the upper voltage bus and the second switching transistor being connected from the common node to the lower voltage bus; a first capacitor connected, at one end, to the common node of the series coupled pair of switching transistors; a first diode having an anode connected to an opposite end of the first capacitor, and a cathode; a second capacitor coupled from the cathode of the first diode to the lower voltage bus; a second diode having an anode coupled to the upper voltage bus, and a cathode connected to the cathode of the first capacitor and the anode of the first diode; a spark gap having opposing ends and being coupled, at one end, to the cathode of the first diode; a pulse transformer having a primary winding coupled from the opposite end of the spark gap to the lower voltage bus and a secondary winding for connecting across the HID lamp; and a control circuit operable to alternatively turn on and off the first and second switching transistors, such that the spark gap is operable to deliver the pulse of current to the primary winding of the pulse transformer in synchronism with the turn on of the first switching transistor.
REFERENCES:
patent: 4904907 (1990-02-01), Allison et al.
patent: 5036256 (1991-07-01), Garrison et al.
patent: 5051665 (1991-09-01), Garrison et al.
patent: 5391966 (1995-02-01), Garrison
patent: 5534753 (1996-07-01), Blom et al.
International Rectifier Corp.
Ostrolenk Faber Gerb & Soffen, LLP
Philogene Haissa
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