Solid state chopper ballast for gaseous discharge lamps

• US 3,890,537 A
• Filed: 01/02/1974
• Issued: 06/17/1975
• Est. Priority Date: 01/02/1974
• Status: Expired due to Term

• Current Assignee: John N. Park, Robert L. Steigerwald, Steven C. Peak
• Original Assignee: John N. Park, Robert L. Steigerwald, Steven C. Peak
• Inventors: Peak, Steven C., Park, John N., Steigerwald, Robert L.
• Primary Examiner(s): Demeo, Palmer C.
• Assistant Examiner(s): LaRoche, E. R.
• Application Number:
  US05/430,088
• Time in Patent Office: 531 Days
• Field of Search: 315/2R,207,208,224,287,283,307,DIG.5,DIG.7,29R
• US Class Current: 315/208
• CPC Class Codes: H02M 1/4208 Arrangements for improving power factor of AC input
• CPC Class Codes: H05B 41/28 using static converters
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

A single phase, high frequency, transistor or gate turnoff thyristor chopper ballast circuit especially suited for mercury vapor lamps preferably operates on a unfiltered full wave rectified line voltage and electronically shapes the lamp current and therefore the line current to obtain a high power factor. The ballast circuit is lightweight with low volume due to elimination of large low frequency energy storage, filtering, and transformer components. The forced, high frequency ripple lamp current waveshape, achieved by comparison of the sensed current with an appropriate reference signal, provides for good regulation, an initially high starting current to eliminate glow-to-arc mode, automatic sweeping of the chopping frequency to avoid acoustic resonance effects, and a minimum current in the valley regions of the supply voltage for improved reignition characteristics.

Claims

1. A solid state ballast circuit for gaseous discharge lamps comprising a solid state chopper circuit for energization by low frequency alternating-current line voltage anD line current and including high frequency filter means for supplying sinusoidal power voltage between a pair of supply terminals and controlled switching means and coasting device means effectively coupled to said supply terminals and coasting inductor means to be conductive alternately to supply lamp current through said coasting inductor means to a gaseous discharge lamp, current sensor means coupled to sense the instantaneous lamp current and produce a sensor signal indicative thereof, a control circuit comprising generating means for generating a reference signal with a preselected waveshape and magnitude to determine the power level and to effect shaping of said lamp current and therefore the line current to obtain a high power factor, comparing means for effectively comparing said sensor and reference signals and producing an output signal, and means actuated by said output signal for supplying turn-on and turnoff signals to operate said controlled switching means at a variable high frequency chopping rate and shape said lamp current as determined by said reference signal, said control circuit further comprising means for temporarily shaping and increasing the magnitude of said reference signal at start-up to obtain a high starting lamp current, and said control and chopper circuits further comprising means for supplying minimum lamp current for good reignition characteristics during the low voltage regions of said line voltage in each cycle when said comparing means is ineffective to shape the lamp current.

2. A solid state ballast according to claim 1 additionally including an adaptive control circuit connected with said generating means to further shape said reference signal according to a selected control.

3. A solid state ballast according to claim 1 wherein said generating means is comprised by a transformer energized by the low frequency line voltage for deriving a control voltage, and control function generator means for regulating and shaping said control voltage according to a predetermined control function to produce said reference signal, said control function generator means further including said means for temporarily shaping said reference signal at start-up to obtain a high starting lamp current.

4. A solid state ballast according to claim 3 wherein said comparing means includes a comparator with hysteresis, and said comparator has a series pass transistor regulator low voltage power supply energized by said transformer which supplies regulated clipped voltage to said comparator except during the low voltage regions of the line voltage.

5. A solid state ballast according to claim 1 wherein said generating means is comprised by means energized by the low frequency line voltage for deriving a control voltage in phase with the line voltage, and control function generator means for shaping said control voltage according to a predetermined control function to produce said reference signal, said control function generator means further including said means for temporarily shaping said reference signal at start-up to obtain the high starting lamp current.

6. A solid state ballast according to claim 5 wherein said means for temporarily shaping said reference signal at start-up is provided by a long time constant resistor-capacitor network for temporarily modifying operation of said control function generator means.

7. A solid state ballast according to claim 6 wherein said comparing means includes a comparator with hysteresis, and said comparator has low voltage power supply means energized by said means for deriving a control voltage which supplies regulated voltage to said comparator except during the low voltage regions of the line voltage.

8. A solid state ballast circuit for gaseous discharge lamps comprising a solid state chopper circuit for energization by low frequency alternating-current line voltage and line current and including full wave rectifying means and high frequenCy filter means for supplying rectified sinusoidal power voltage between a pair of unidirectional voltage supply terminals, and further including a power transistor and coasting diode connected in series between said supply terminals that conduct alternately and supply lamp current through a coasting inductor and gaseous discharge lamp that in turn are connected in series across said coasting diode, current sensor means coupled to sense the instantaneous lamp current and produce an instantaneous sensor signal indicative thereof, a control circuit comprising a transformer and a first bridge rectifier energized by the low frequency line voltage for generating full wave rectified sinusoidal control voltage, a control function generator circuit for shaping said control voltage and generating a symmetrically curved reference signal with a waveshape and magnitude selected to determine the power level and to effect shaping of the lamp current and therefore the line current to obtain a high power factor in excess of 90 percent, a comparator circuit with hysteresis for effectively comparing said sensor and reference signals and producing an output signal, a second bridge rectifier connected to said transformer for deriving full wave rectified sinusoidal base drive power supply voltage, a positive and negative base drive circuit connected to said second bridge rectifier for supplying alternate turn-on and turn-off signals to said power transistor with a base current proportional to collector current, and means for coupling said comparator output signal to energize said negative base drive circuit and de-energize said positive base drive circuit to thereby operate said power transistor at a variable high frequency chopping rate and effect shaping of the lamp current as determined by said reference signal waveshape, said control circuit further comprising means for temporarily shaping and increasing the magnitude of said reference signal at start-up to obtain a high starting lamp current, and said control and chopper circuits further comprising means for supplying minimum lamp current for good reignition characteristics during the valleys of the rectified sinusoidal power voltage when said comparator circuit is ineffective to shape the lamp current.

9. A solid state ballast according to claim 8 wherein said comparator circuit has a low voltage power supply circuit energized by said transformer that is operative to clip the full wave rectified control voltage at a selected low voltage level and supply power to said comparator circuit except during the valleys of the rectified sinusoidal power voltage.

10. A solid state ballast according to claim 8 wherein said chopper circuit has a pair of input terminals and said high frequency filter means includes a shunt capacitor and series inductor connected between said input terminals and full wave rectifying means, and a polycrystalline varistor connected between the input terminals of said full wave rectifying means, said transformer likewise having a primary winding connected between the input terminals of said full wave rectifying means, to thereby provide filtering and protection for both the control circuit and chopper circuit.

11. A solid state ballast according to claim 8 wherein said comparator circuit has at least one series pass transistor regulator low voltage power supply circuit energized by said transformer that is operative to clip the full wave rectified control voltage at a selected low voltage level and supply power to said comparator circuit except during the valleys of the rectified sinusoidal power voltage.

12. A solid state ballast according to claim 8 wherein said control function generator circuit is comprised by a resistive voltage divider circuit having a variable resistance branch including and controlled by an insulated-gate field effect transistor, and said means for temporarily shaping said reference signal at start-up to obtain a high starting lamp current is providEd by a long time constant resistor-capacitor network connected to the gate of said field effect transistor for temporarily determining the gate voltage and therefore the resistance of said field effect transistor. l

13. A solid state ballast according to claim 8 wherein said control function generator circuit is comprised by a resistive voltage divider circuit having a variable resistance branch including and controlled by an insulated-gate field effect transistor, and further comprises a control voltage peak detector circuit connected to the gate of said field effect transistor for determining the gate voltage and therefore the resistance of said field effect transistor to thereby provide automatic gain control of said reference signal to regulate the lamp current, said peak detector circuit having a long time constant to thereby provide said means for temporarily shaping said reference signal at start-up to obtain a high starting lamp current.

14. A solid state ballast according to claim 8 wherein said positive base drive circuit is connected to said second bridge rectifier to be normally conductive in the absence of said comparator output signal, and said means for supplying minimum lamp current during the valleys of the rectified sinusoidal power voltage includes local energy storage capacitors coupled to said second bridge rectifier and to a reference point that discharge to provide base current to maintain conductivity of said power transistor during the power voltage valleys, said high freguency filter means including a filter capacitor connected between said unidirectional voltage supply terminals which supplies lamp current during the power voltage valleys.

15. A solid state ballast according to claim 8 wherein said control function generator circuit is comprised by a resistive voltage divider circuit having a variable resistance branch including an insulated-gate field effect transistor, and an adaptive control circuit connected to the gate of said field effect transistor to determine the gate voltage and therefore the resistance of said field effect transistor to further shape said reference signal according to a selected control.