CA2141617A1 - Florescent tube driver and lighting system - Google Patents
Florescent tube driver and lighting systemInfo
- Publication number
- CA2141617A1 CA2141617A1 CA 2141617 CA2141617A CA2141617A1 CA 2141617 A1 CA2141617 A1 CA 2141617A1 CA 2141617 CA2141617 CA 2141617 CA 2141617 A CA2141617 A CA 2141617A CA 2141617 A1 CA2141617 A1 CA 2141617A1
- Authority
- CA
- Canada
- Prior art keywords
- arc
- tube
- current
- voltage
- driver
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/295—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
- H05B41/298—Arrangements for protecting lamps or circuits against abnormal operating conditions
- H05B41/2981—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions
- H05B41/2985—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions against abnormal lamp operating conditions
Abstract
2141617 9404011 PCTABS00030 The invention is concerned with a fluorescent tube driver arranged to be supplied by a direct voltage source (particularly a voltage source less than 50 volts, preferably 24 volts nominal) and having a tube drive output in the range 10 to 100 watts of arc power (preferably 10 to 40 watts) with a frequency of oscillation in the range 15 to 50 KHz (preferably 32 KHz nominal), the driver comprising an arc waveform transformer (22), the primary winding (23) of which is supplied with a variable drive current derived from the low voltage source (15), and the secondary winding (25) of which is adapted to be connected to the electrodes (13, 14) of a fluorescent tube (12), such that in use an alternating tube arc current will flow through the secondary winding and tube. The drive includes a closed loop control system (31-44) provided for maintaining substantially constant the tube arc current by varying the amplitude of the arc current waveform without varying the pulse width. This extends the tube life and reduces the wasted heat.
The arc transformer driver (24) and arc current are selected to give a symmetrical arc waveform with a constant waveform duty cycle in the range 90 to 95 %, and a tube arc power less than 90 % of the rated tube power, and to maintain at a constant value in the range 1.3 to 1.5 the arc crest factor.
The arc transformer driver (24) and arc current are selected to give a symmetrical arc waveform with a constant waveform duty cycle in the range 90 to 95 %, and a tube arc power less than 90 % of the rated tube power, and to maintain at a constant value in the range 1.3 to 1.5 the arc crest factor.
Description
FLUORESCE~T TUBE DRIYER AND LIG~T NG SYSTE~
BACKGROUND OF T~E INVENTION
This in~ention relates to a fluorescent t~be driver and a fluorescent lighting system including such a dri~er.
The invention is concerned with a dri~er working from a direct voltage supply, prefera~ly but not essentially a low voltage supply (less than 50 volts) and including an oscillator circuit producing a relatively high frequency oscillation (15 to 50 KHz preferably 25 to 50 KHz3 and including a tran f~rmer supplying arc ourrent to the fluorescent tube. Known cirCuitC operating from a s~irect voltage supply at a high frequency are described for example in UK Patent Speoifications 1010208, 1308578, 2126810, 2246034r 2244608, 2212g95 and 2095930. However these operate by controlling the current to the driver by varying the pulse width or the fre~uency of the drive signal.
US-A-4723098 which is regarded as the closest prior art describes a driver circuit with a closed loop control system but this adjusts the frequency of the drive signal which inevitably varies the arc curren~ crest factor.
US-A-4862040 also describes a driver circuit in which the frequency of the drive signal is varied.
~ he present invention particularly aims to proYide a driver capable of operating at high efficie~cy and which is particularly suited for use in heat conscious and energy sa~ing ~n~ironments. Additionally the invention aims to produce a driver which will promote optimum tube life.
SummarY of the Invention T~e in~ention is particularly concerned with a fluore-~cent tube driver arranged to be supplied by a direct voltage source tparticularly a voltage source less than 50 volts, preferably 24 Yolts nominal) and having a tube driver output in the range 10 to 100 watts of arc power (preferably AhtENOED SHEET
r ~ ~ r ! ~~a 10 to 40 watts) with a frequency of oscillation in the range to 50 KHz ~preferably 32 KHz nominal), the driYer comprising an arc waveform trans~ormer, the primary winding of which is supplied with a variab~e dri~e current derived from the low ~oltage source, and the secondary winding of which is adapted to be connected to the electrodes of a :.
.~
AbNDED Sl !EET
WO94/04011 21 416 17 2 PCT~GB93/01618 ~luorescen~ tube, such tha~ in use an altern~ting tube arc current will flow throuah the secondary winding and tube.
The driver of the present invention is of the above type and has a number of novel and ad~antageous features which may be claimed independently or in any combination. These are as follows:
A closed loop control sys~em is provided for maintaining substantially constant the tube arc current by varying the amplitude of the arc current waveform. This ?referably comprises means for measuring the arc current flowing through the secondary winding and tube to produce a ~easured signal representing actual arc current supply, means for generating 2 reference signal representing desired arc c~rrent, comparator means for comparing the measureà signal and the reference signal and producing an error signal, and a current adjus~ment means responsive to the error signal for deriving the drive current such as to maintain the tube arc current constant.
A tube arc current ~onstantly held at the right level j extends the tube life. Insufficient arc current results in a lack of anode fall voltage across the electrodes resulting in insufficient electrode temperature, which in turn results in much reduced electrode life and hence reduced tube life due to inefficient operation of the electrodes. Excessive arc current resul~s in electrode over dissipation and hence reduced electrode life.
The closed loop arc current control system utilises a true current servo system rather than a pulse width modulation system. This has the advantage that the arc wave form duty cycle is constant which in turn results in a constant arc current crest factor irrespective of the degree of correction introduced by the error amplifier. The net gain is that tube life variation due to varying crest factor is eliminated.
The arc current crest factor is the ratio of peak to ~MS arc current. The greater this figure, the greater is the stress to the tube electrodes during tube operation. Stress 21~1~17 to the electrodes results in loss of electron emissive material from the electrode surface which is deposite~ on the tube wall and is-observed as tube l'end blackening". In a preferred form of the present invention a crest current factor of l.3 to l.5 is achieved, dependent upon the tube type.
The driver is arranged to produce a fully symmetrical tube arc wave form. This prevents the phenomena of mercury vapour migration within ~he tube. Mercury vapour migration ultimately results in light output reduction at one end of the tube necessitating tube replacement. A fully symmetrical arc wave form prevents mercury vapou- migration and ultimately results in increased tube life. -~
The closed loop arc current control system of the `~
invention holds the arc current constant over a wide range of DC supply voltages (typically 22 to 33 volts DC for a nominal 24 volt supply) . `
As the tube volt-ampere characteristic is only -temperature dependent, it is inherent that holding tube arc current constant results in constant tube arc power and hence ~ constant light output at a given temperature. Thus the i operating arc power and the light output can be selected to suit the individual application.
For example, in an energy saving, heat dissipation conscious application of the driver of the invention, the selected ~alue of arc current may be selected such that the tube light output is a percentage, less than lO0, (preferably 80 to 90%~ of rated output e.g. 87 per cent. This allows one to choose a required combination of tube radiated heat, tube light output and unit power consumption. By selecting and controlling the tube arc current one contols the tube arc power. However the arc current selected should fall within the tube preferred range.
The driver is particularly designed for temperature sensitive situations, for example where the tube is to light shelving, confined spaces or refrigeration units.
Independently of the closed loop control therefore the WO94/04011 2141~17 PCT/GB93/01618 invention concerns a driver which is arranged to run a tube at tube arc power of 80 to 90% of the tube rated power and at a constant arc current crest factor below l.7 and preferably in the range l.5 to l.3.
The means for providin~ ~the reference signal compriseS a resistive, divide~derived, voltage from a reference voltage. Selection of~the appropriate divider is via a jumper link system. The tap position by which the tube is connected to the secondary winding of the arc transformer is preferably also selected by a jumper link selection system. By these means a wide variety of tube types and styles can be used and the exactly right conditions for each can be selected in seconds. In order to adjust the driver for the selected tube type, two header selections must be made. The first selection is used to select one of a number (six to eight for example) of resistor 2airs which determine the tube arc current~ The second selection is used to select one of a number of taps from the transformer secondary driving the tube arc. This second selection i5 necessary in order to ensure compliance with the tube operating arc voltage. With this arrangement the design is capable of driving tubes within the range lO to 40 watts and all th~t is required to tailor the system to a specific tube is the correct selection of the arc current resistor pair and the c~rrect selection of the transformer tap position.
The arc current flow circuit includes no dissipating device forming an arc current limiting element and this leads to higher efficiency. Efficiencies in the range 80 to 85 per cent are normally achieved with the circuit described.
The drive voltage adjustment means comprises a low differential current source having a voltage output V2 and a switched mode power supply unit, arranged to receive the supply voltage V and having an output voltage Vl arranged to be supplied to the low differential current supply unit. The voltages V2 and Vl are measured by the switched mode supply unit which is arranged to hold the current source differential V2 minus Vl constant. The current source is 2141617 ~
-, WO94/04011 ~rogrammed by the error slgnal and the switched mode supply unit is programmed from the current source. The switched mode power supply unit again gives high efficiency of operation. The switched mode approach also allows the unit a wide operating voltage range of 22 to 33 the volts DC for a nominal input voltage of 24 volts.
The high efficiency enables the use of the driver in confined spaces where excessive heat generation would be a ~roblem and in energy saving situations.
A strike oscillator is provided for providing a strike voltage, higher than the arc drive voltage, to the tube arc at start up. Additionally a heater circuit is provided for providlng a current through the electrodes to heat these for a short period before each strike up attempt.
For example a strike up attempt may consist of electrode ?reheating for a period e.g. approximately l.5 seconds followed by the application of a high vol~age strike pulse across the tube arc. According to another feature of the invention means are provided for detecting whether or not the tube strikes. If the tube strikes the strike oscillator is disabled and the arc transformer driver enabled and the closed loop arc current control will become operative. If the tube fails to strike the arc transformer driver continues to drive but will be inhibited after a brief pause period of or example approximately 2.5 seconds. The strike sequence will then be reinitiated, that is the preheating followed by the application of strike voltage is repeated. Means are provided for repeating this sequence for a predetermined number of strike attempts, for example 6 to 8, following which the attempt sequence will be terminated. If striking does not occur during this sequence the unit will shut down and remove potential from the tube terminals. A shut down would, for example, result with a worn out tube or if the tube were absent. A shut down may be reset by removal and reapplication of power.
Should a tube be removed during operation or become extinguished for any other reason then the system is arranged - . : - . : - . ...... :.. -WO94~04011 2 1 ~1 6 1~ 6 PCT/GB93/01618 to re-enter restrike mode wnereby the strike attempt sequence will restart. If the tube is replaced within the predetermined duration (e.g. 25 seconds) then the tube will be restruck. If the tube is not replaced the system will shut down. This feature enables carefu;l tube changing whilst the system is running provided that one is aware of the potential hazards involved.
~rief Description of ~he Drawings One embodiment of fluorescent tube driver and lighting system, in accordance with the invention, will now be described, by way of example only, with reference to the accompanying drawings of which:-Figure l is a bloc~ circuit diagram of a driver andtu~e, Figure 2 shows a plot of arc current and arc voltage provided by the driver of Figure l, Figure 3 show details of the circuitry of Figure l and is divided into parts 3a to 3f which fit together as seen in Figure 3, Figure 4 shows the bobbin of the arc transformer of Figure l, and Figure 5 shows the bobbin of the electrode transformer of Figure l.
Detailed Description of one Embodiment . _ . .
Referring to the ~lock diagram of ~igure l, a hot cathode fluorescent tube 12 has electrodes 13, 14 and is arranged to be dri~en from a 24 volt nominal DC supply lS as the power source. In order ~o preheat the electrodes before stri~e up, sespective electrodes 13, 14 are connected in series with secondary windings 16, 17 of an electrode heating transformer 18, the primary winding 20 of which has an intermediate part l9 thereof connected to the DC supply 15.
The ends of the primary winding are connected to an electrode ~141617 ~
tranformer push/pull driver 21.
A tube arc waveform transformer 22 has a primary winding 23 connected across an arc ~ransformer push/pull driver 24 and has a secondary winding 25 one end 26 of which is connected via line ~7 and a resistor Rs to the electrode 14 to provide the tube arc current supply. An arc transformer jumper tap selection unit 28 connects a selected tap off point of the secondary winding 25 via line 30 to the electrode 13.
Lines 31, 32 connected across the resistor Rs provide an input measure of the arc current wave form to the input of an RMS-DC convertor 33, the output of which, on line 34, provides a DC voltage signal (representing the measured RMS
ar~ c~rrent which is normally in the range 230 to 285 mA) to one lnput of an integrating error am~lifier 35. The output from this circuit is a DC voltage proportional to the RMS
tube arc current on a l:l basis ie one volt DC equals one amp RMS of arc current. A reference voltage source 36 provides a reference voltage of 15 volts and this is connected via a resistor 37 to a jumper switch RMS arc current selector header unit 38 with the connection between resistor 37 and unit 38 connected to the other input of the integrating error amplifier 35. The RMS arc current selection header unit 38 comprises a plurality of resistors in parallel connected to earth and the jumper switch allows one of these dividers to be tapped thus providing a selected RMS arc current programme voltage (on the basis of one volt equals one amp) to the other input of the integrating error amplifier. The output (error signal) from the amplifier 35 is connected on line 40 to a programme input 39 of a low differential current source unit 41, the current output of which is connected by line 42 and diode 43 to an interme~iate connection of the primary winding 23 of the arc transformer 22. This current I is the driYe current to the arc transformer (l~2 to 2 amps). A
swit~hed mode voltage source unit 44 has an input voltage V
(nominally 24 volts) on line 45 from the DC supply l5 and an output voltage Vl on line 46 which is supplied as an input to wo 94~04011 2 1 4 1 6 17 8 PCT/GB93/U1618 ~;
the low differential current source unit 41. The voltages on lines 46 and 42 are fed back to the voltage source unit 44 which is arranged to hold the current source differential Vl minus V2 constant.
A strike oscillator 47 is!connected via diode 48 and line 49 to the midpoint of th~;primary winding 23 of the transformer 22. A strike capa~ tor Cs is connected between the line 49 and earth and is~~arranged to be charged up by the strike oscillator.
A system control unit 50 includes a multi-strike attempt timing circuit 51 and a "give up" circuit 52, each connected to receive a start up signal on line 53 from a power up reset/start switch unit 54. The timing circuit 51 has a phase l output on line 55A to enable the electrode transformer driver 21 and the strike oscillator 47, and a ?hase 2 output on line 55B to enable the arc transformer driver 24. The give up circuit 5~ has an o~tput on line 56 arranged to give a shut down signal to the circuits 51, 21 and 24. The output of the error amplifier 35 is also connected-on line 57 to an input of the multi-strike attempt timing circuit 51 and the give up circuit 52 to indicate whether or not the tube has been struck. A short circuit overload shut down circuit 58 is connected across the lines 3l, 32 and arranged to detect a short circuit and when so detected to supply a shut down signal to the programme input of the low differential current source 41.
As indicated at the top of Figure l the circuit DC
supply 15 is derived from an original DC supply 60 via a reverse polarity over current protection unit 61 and a filtering unit 62.
The system operates as follows. On system power up, the power up reset generator 54 issues a reset/start pulse to the system controller 50.
Initially, the system controller enters phase one which involves enabling the strike oscillator and enabling the ~ube-end electrode pre-heat system. The strike oscillator is a simple flyback convertor which is used to , .:,, ,,,, . . , ... , ... ... , . , , . , . ~ .. . . ... . . .
BACKGROUND OF T~E INVENTION
This in~ention relates to a fluorescent t~be driver and a fluorescent lighting system including such a dri~er.
The invention is concerned with a dri~er working from a direct voltage supply, prefera~ly but not essentially a low voltage supply (less than 50 volts) and including an oscillator circuit producing a relatively high frequency oscillation (15 to 50 KHz preferably 25 to 50 KHz3 and including a tran f~rmer supplying arc ourrent to the fluorescent tube. Known cirCuitC operating from a s~irect voltage supply at a high frequency are described for example in UK Patent Speoifications 1010208, 1308578, 2126810, 2246034r 2244608, 2212g95 and 2095930. However these operate by controlling the current to the driver by varying the pulse width or the fre~uency of the drive signal.
US-A-4723098 which is regarded as the closest prior art describes a driver circuit with a closed loop control system but this adjusts the frequency of the drive signal which inevitably varies the arc curren~ crest factor.
US-A-4862040 also describes a driver circuit in which the frequency of the drive signal is varied.
~ he present invention particularly aims to proYide a driver capable of operating at high efficie~cy and which is particularly suited for use in heat conscious and energy sa~ing ~n~ironments. Additionally the invention aims to produce a driver which will promote optimum tube life.
SummarY of the Invention T~e in~ention is particularly concerned with a fluore-~cent tube driver arranged to be supplied by a direct voltage source tparticularly a voltage source less than 50 volts, preferably 24 Yolts nominal) and having a tube driver output in the range 10 to 100 watts of arc power (preferably AhtENOED SHEET
r ~ ~ r ! ~~a 10 to 40 watts) with a frequency of oscillation in the range to 50 KHz ~preferably 32 KHz nominal), the driYer comprising an arc waveform trans~ormer, the primary winding of which is supplied with a variab~e dri~e current derived from the low ~oltage source, and the secondary winding of which is adapted to be connected to the electrodes of a :.
.~
AbNDED Sl !EET
WO94/04011 21 416 17 2 PCT~GB93/01618 ~luorescen~ tube, such tha~ in use an altern~ting tube arc current will flow throuah the secondary winding and tube.
The driver of the present invention is of the above type and has a number of novel and ad~antageous features which may be claimed independently or in any combination. These are as follows:
A closed loop control sys~em is provided for maintaining substantially constant the tube arc current by varying the amplitude of the arc current waveform. This ?referably comprises means for measuring the arc current flowing through the secondary winding and tube to produce a ~easured signal representing actual arc current supply, means for generating 2 reference signal representing desired arc c~rrent, comparator means for comparing the measureà signal and the reference signal and producing an error signal, and a current adjus~ment means responsive to the error signal for deriving the drive current such as to maintain the tube arc current constant.
A tube arc current ~onstantly held at the right level j extends the tube life. Insufficient arc current results in a lack of anode fall voltage across the electrodes resulting in insufficient electrode temperature, which in turn results in much reduced electrode life and hence reduced tube life due to inefficient operation of the electrodes. Excessive arc current resul~s in electrode over dissipation and hence reduced electrode life.
The closed loop arc current control system utilises a true current servo system rather than a pulse width modulation system. This has the advantage that the arc wave form duty cycle is constant which in turn results in a constant arc current crest factor irrespective of the degree of correction introduced by the error amplifier. The net gain is that tube life variation due to varying crest factor is eliminated.
The arc current crest factor is the ratio of peak to ~MS arc current. The greater this figure, the greater is the stress to the tube electrodes during tube operation. Stress 21~1~17 to the electrodes results in loss of electron emissive material from the electrode surface which is deposite~ on the tube wall and is-observed as tube l'end blackening". In a preferred form of the present invention a crest current factor of l.3 to l.5 is achieved, dependent upon the tube type.
The driver is arranged to produce a fully symmetrical tube arc wave form. This prevents the phenomena of mercury vapour migration within ~he tube. Mercury vapour migration ultimately results in light output reduction at one end of the tube necessitating tube replacement. A fully symmetrical arc wave form prevents mercury vapou- migration and ultimately results in increased tube life. -~
The closed loop arc current control system of the `~
invention holds the arc current constant over a wide range of DC supply voltages (typically 22 to 33 volts DC for a nominal 24 volt supply) . `
As the tube volt-ampere characteristic is only -temperature dependent, it is inherent that holding tube arc current constant results in constant tube arc power and hence ~ constant light output at a given temperature. Thus the i operating arc power and the light output can be selected to suit the individual application.
For example, in an energy saving, heat dissipation conscious application of the driver of the invention, the selected ~alue of arc current may be selected such that the tube light output is a percentage, less than lO0, (preferably 80 to 90%~ of rated output e.g. 87 per cent. This allows one to choose a required combination of tube radiated heat, tube light output and unit power consumption. By selecting and controlling the tube arc current one contols the tube arc power. However the arc current selected should fall within the tube preferred range.
The driver is particularly designed for temperature sensitive situations, for example where the tube is to light shelving, confined spaces or refrigeration units.
Independently of the closed loop control therefore the WO94/04011 2141~17 PCT/GB93/01618 invention concerns a driver which is arranged to run a tube at tube arc power of 80 to 90% of the tube rated power and at a constant arc current crest factor below l.7 and preferably in the range l.5 to l.3.
The means for providin~ ~the reference signal compriseS a resistive, divide~derived, voltage from a reference voltage. Selection of~the appropriate divider is via a jumper link system. The tap position by which the tube is connected to the secondary winding of the arc transformer is preferably also selected by a jumper link selection system. By these means a wide variety of tube types and styles can be used and the exactly right conditions for each can be selected in seconds. In order to adjust the driver for the selected tube type, two header selections must be made. The first selection is used to select one of a number (six to eight for example) of resistor 2airs which determine the tube arc current~ The second selection is used to select one of a number of taps from the transformer secondary driving the tube arc. This second selection i5 necessary in order to ensure compliance with the tube operating arc voltage. With this arrangement the design is capable of driving tubes within the range lO to 40 watts and all th~t is required to tailor the system to a specific tube is the correct selection of the arc current resistor pair and the c~rrect selection of the transformer tap position.
The arc current flow circuit includes no dissipating device forming an arc current limiting element and this leads to higher efficiency. Efficiencies in the range 80 to 85 per cent are normally achieved with the circuit described.
The drive voltage adjustment means comprises a low differential current source having a voltage output V2 and a switched mode power supply unit, arranged to receive the supply voltage V and having an output voltage Vl arranged to be supplied to the low differential current supply unit. The voltages V2 and Vl are measured by the switched mode supply unit which is arranged to hold the current source differential V2 minus Vl constant. The current source is 2141617 ~
-, WO94/04011 ~rogrammed by the error slgnal and the switched mode supply unit is programmed from the current source. The switched mode power supply unit again gives high efficiency of operation. The switched mode approach also allows the unit a wide operating voltage range of 22 to 33 the volts DC for a nominal input voltage of 24 volts.
The high efficiency enables the use of the driver in confined spaces where excessive heat generation would be a ~roblem and in energy saving situations.
A strike oscillator is provided for providing a strike voltage, higher than the arc drive voltage, to the tube arc at start up. Additionally a heater circuit is provided for providlng a current through the electrodes to heat these for a short period before each strike up attempt.
For example a strike up attempt may consist of electrode ?reheating for a period e.g. approximately l.5 seconds followed by the application of a high vol~age strike pulse across the tube arc. According to another feature of the invention means are provided for detecting whether or not the tube strikes. If the tube strikes the strike oscillator is disabled and the arc transformer driver enabled and the closed loop arc current control will become operative. If the tube fails to strike the arc transformer driver continues to drive but will be inhibited after a brief pause period of or example approximately 2.5 seconds. The strike sequence will then be reinitiated, that is the preheating followed by the application of strike voltage is repeated. Means are provided for repeating this sequence for a predetermined number of strike attempts, for example 6 to 8, following which the attempt sequence will be terminated. If striking does not occur during this sequence the unit will shut down and remove potential from the tube terminals. A shut down would, for example, result with a worn out tube or if the tube were absent. A shut down may be reset by removal and reapplication of power.
Should a tube be removed during operation or become extinguished for any other reason then the system is arranged - . : - . : - . ...... :.. -WO94~04011 2 1 ~1 6 1~ 6 PCT/GB93/01618 to re-enter restrike mode wnereby the strike attempt sequence will restart. If the tube is replaced within the predetermined duration (e.g. 25 seconds) then the tube will be restruck. If the tube is not replaced the system will shut down. This feature enables carefu;l tube changing whilst the system is running provided that one is aware of the potential hazards involved.
~rief Description of ~he Drawings One embodiment of fluorescent tube driver and lighting system, in accordance with the invention, will now be described, by way of example only, with reference to the accompanying drawings of which:-Figure l is a bloc~ circuit diagram of a driver andtu~e, Figure 2 shows a plot of arc current and arc voltage provided by the driver of Figure l, Figure 3 show details of the circuitry of Figure l and is divided into parts 3a to 3f which fit together as seen in Figure 3, Figure 4 shows the bobbin of the arc transformer of Figure l, and Figure 5 shows the bobbin of the electrode transformer of Figure l.
Detailed Description of one Embodiment . _ . .
Referring to the ~lock diagram of ~igure l, a hot cathode fluorescent tube 12 has electrodes 13, 14 and is arranged to be dri~en from a 24 volt nominal DC supply lS as the power source. In order ~o preheat the electrodes before stri~e up, sespective electrodes 13, 14 are connected in series with secondary windings 16, 17 of an electrode heating transformer 18, the primary winding 20 of which has an intermediate part l9 thereof connected to the DC supply 15.
The ends of the primary winding are connected to an electrode ~141617 ~
tranformer push/pull driver 21.
A tube arc waveform transformer 22 has a primary winding 23 connected across an arc ~ransformer push/pull driver 24 and has a secondary winding 25 one end 26 of which is connected via line ~7 and a resistor Rs to the electrode 14 to provide the tube arc current supply. An arc transformer jumper tap selection unit 28 connects a selected tap off point of the secondary winding 25 via line 30 to the electrode 13.
Lines 31, 32 connected across the resistor Rs provide an input measure of the arc current wave form to the input of an RMS-DC convertor 33, the output of which, on line 34, provides a DC voltage signal (representing the measured RMS
ar~ c~rrent which is normally in the range 230 to 285 mA) to one lnput of an integrating error am~lifier 35. The output from this circuit is a DC voltage proportional to the RMS
tube arc current on a l:l basis ie one volt DC equals one amp RMS of arc current. A reference voltage source 36 provides a reference voltage of 15 volts and this is connected via a resistor 37 to a jumper switch RMS arc current selector header unit 38 with the connection between resistor 37 and unit 38 connected to the other input of the integrating error amplifier 35. The RMS arc current selection header unit 38 comprises a plurality of resistors in parallel connected to earth and the jumper switch allows one of these dividers to be tapped thus providing a selected RMS arc current programme voltage (on the basis of one volt equals one amp) to the other input of the integrating error amplifier. The output (error signal) from the amplifier 35 is connected on line 40 to a programme input 39 of a low differential current source unit 41, the current output of which is connected by line 42 and diode 43 to an interme~iate connection of the primary winding 23 of the arc transformer 22. This current I is the driYe current to the arc transformer (l~2 to 2 amps). A
swit~hed mode voltage source unit 44 has an input voltage V
(nominally 24 volts) on line 45 from the DC supply l5 and an output voltage Vl on line 46 which is supplied as an input to wo 94~04011 2 1 4 1 6 17 8 PCT/GB93/U1618 ~;
the low differential current source unit 41. The voltages on lines 46 and 42 are fed back to the voltage source unit 44 which is arranged to hold the current source differential Vl minus V2 constant.
A strike oscillator 47 is!connected via diode 48 and line 49 to the midpoint of th~;primary winding 23 of the transformer 22. A strike capa~ tor Cs is connected between the line 49 and earth and is~~arranged to be charged up by the strike oscillator.
A system control unit 50 includes a multi-strike attempt timing circuit 51 and a "give up" circuit 52, each connected to receive a start up signal on line 53 from a power up reset/start switch unit 54. The timing circuit 51 has a phase l output on line 55A to enable the electrode transformer driver 21 and the strike oscillator 47, and a ?hase 2 output on line 55B to enable the arc transformer driver 24. The give up circuit 5~ has an o~tput on line 56 arranged to give a shut down signal to the circuits 51, 21 and 24. The output of the error amplifier 35 is also connected-on line 57 to an input of the multi-strike attempt timing circuit 51 and the give up circuit 52 to indicate whether or not the tube has been struck. A short circuit overload shut down circuit 58 is connected across the lines 3l, 32 and arranged to detect a short circuit and when so detected to supply a shut down signal to the programme input of the low differential current source 41.
As indicated at the top of Figure l the circuit DC
supply 15 is derived from an original DC supply 60 via a reverse polarity over current protection unit 61 and a filtering unit 62.
The system operates as follows. On system power up, the power up reset generator 54 issues a reset/start pulse to the system controller 50.
Initially, the system controller enters phase one which involves enabling the strike oscillator and enabling the ~ube-end electrode pre-heat system. The strike oscillator is a simple flyback convertor which is used to , .:,, ,,,, . . , ... , ... ... , . , , . , . ~ .. . . ... . . .
2 1 4 1 6 1 7 PCT/GBg3/01618 charge the strike capacitor, Cs~ to approximately 91 volts which is later stepped up by the arc transformer to generate a high tension tu~e strike potential.
The electrode pre-heat system consists of a push-pull step down transformer configuration generating two galvanically isolated electrode pre-heat voltages.
During phase one which is of approximately l.5 seconds duration, the main arc transformer push-pull drive system is disabled.
During phase two, the strike oscillator and th~
electrode pre-heat system are disabled and the arc transformer push-pull drive is enabled. Initially, drive to the arc transformer results in the voltage across Cs being stepped up by the transformer ratio. This results in the generation of a high potential across the tube arc resulting ln a tube strike. The result is a decaying alternating voltage across the tube arc as the strike capacitor discharges.
During initial strike period, a current flow is established into the tube arc which has the effect of activating the sys~em arc current control loop.
Current flowing to the arc results in an alternating arc current wave form across Rs, a measure of which is passed to the RMS to DC convertor 33, the outpu~ from which is a DC
voltage proportional to the RMS tube arc current. The voltage from the RMS output is ~ompared in the error amplifier 35, to a selected programme voltage (at input 39) representing the desired tube RMS arc current. The amplifier output (error signal) on line 40 is utilised to programme the linear low differential current source 41, the resulting output from which is fed to the arc transformer primary winding.
The current flow in the primary winding is stepped down by the transformer ratio to produce an arc current which, in a matter of milliseconds, is adjusted to the value set at the error amplifier programme input 39, by nature of the arc current feedback taken from Rs (as described). This I
?rovides a closed 'oop servo control system maintaining substantially constant the t~be arc current by varying the amplitude of the arc curr~ent waveform.
The net effect is that the tube strike is initiated by the discharge of the strike capacitor but maintained by the arc cuxrent control loop. By nature of the fact that the tube volt/ampere characteristic is fixed, the desired arc current results in a fixed arc power.
If the tube arc fails to strike on application of the stri.~e ~oltage, then a signal from the output of the error amplifier, on line 57, which signal is indicative of a strike failure, is utilised to force the system control circuit to re-e~ter the phase l of the strike procedure and thus restart the strike sequence.
Repetitive strike failure is measured by the give up circuitry 52, which after a predetermined period corresponding to a predetermined number of failures commands a system shut down on line 56, whereby both the electrode and arc drive systems are disabled. This action will occur after approximately 6 to 8 strike attempts or approximately 25 seconds.
The arc transformer programmable current source 41 is of t inear design and is designed to operate at low differential voltages to attain low dissipation. As the output voltage V2 from this current source will be determined by the tube arc voltage as set by the transformer ratio (V2 is typically about 18 volts), and the current source differential will be hundreds of millivolts tVl minus V2 is typically about 0.38 volts), the switched mode power supply 44 is employed to efficiently reduce the 22 to 33 volt ~nominal 24 volts) supply 15 to the voltage attained at Vl.
The switched mode power supply unit monitors the current source differential voltage ~Vl-V2) and holds this ~alue constant irrespective of the voltage of V2 dictated by the tube.
~ t is important to realise that the current source 41 is programmed by the error amplifier 35 and the switched 214161~
WO94/04011 ll PCT/GB93/01618 mode ~ower supply 44 is programmed from the curren~ source in that order.
The ratio- of the arc transformer is selec~ed such that Vp is placed in ~he optimum operating range of 13 to 18 volts.
, The arc transformer push-pull driver 24 is chosen to produce a 90 to 95 per cent duty cycle, symmetrical arc voltage wave form of a frequency 32 KHz nominal. An example of an arc voltage wave form and resulting arc current wave form plot~ed against time, as achieved by the Figure l circ~it is shown in Figure 2. The fixed duty cycle of 90 to 95 per cent, attains the low arc current crest factor of typically l~3 to l.5 dependent on the tube type. The wave form has sharply defined on off characteristics.
The electrode drive push-pull system results in the production of two electrode drive voltages which a~ain are symmetrical and of frequency 36 KHz nominal.
This system is designed to cope with a wide range of standard "off the shelf" tubes and for this purpose it has j the ability to deliver tube arc powers of between lO and 40 watts and is quickly configurable to the desired tube style I by the appropriate placement of the two printed circuit style jumper links 38 and 28 which are used to select tube arc current and tube arc voltage. For example, eight dividers : may be provided for generating the arc current prsgramme ~oltages required for six popular tubes with provision for two spares and four arc transformer tap sele~tion positions are provided in the unit 28. By utilisation of the jumper link selection sys~em, it is possible to select the tube type within seconds. The first selection is used to select one of the number of resistor pairs in the unit 38 which determine the tube arc current. The second selection is used to select one of a number of taps (for example four) from the transformer driving tube arc in the system 28. This second selection is necessary in order to ensure compliance with the tube operating arc voltage. In the circuit described six tubes are catered for with two spare uncommitted tube types.
¦ W094/0401l 2 1 41 6 17 12 PCT/GB93/01618 The six tubes are 18 watt two foot (61cms), 30 watt three foot (91.4cms), 36 watt four foot (121.9cms), 36wp1, 38 watt three foot six inches (106.7cms) and 40wpl. It should be emphasised however that the design is capable of dri~ing any tubes within the range 10 to 40 watts~nd is by no means limited to the above types. ;;~.
Figure 3 shows the implement~ation of the described system which may be related to the block diagram of Figure 1 by reference to the following circuit section descriptions.
Section 1 Switched mode voltage source Section 2 Low differential current source Section 3 Integrating Error ~mplifier Section 4 ~MS to the DC con~ertor Section 5 System control Section 6 RMS arc current selection header and resistors Section 7 Arc transformer push-pull driver - Section 8 Strike oscillator Section 9 Electrode transformer push-pull dri~er Section 10 Electrode transformer Section 11 Ar~ transformer Section 12 Arc transformer tap selection Section 13 Power-up reset circuit Section 14 Short circuit/overload shut-down - With reference to Fiyure 3, the 24 volt nominal DC
supply is applied to Jl-l(+VE) and Jl-3(0V). Dl provides protection from reverse connection of the 24 volt supply.
The four terminal connection to the tube is made at J2. One electrode should be connected to J2-1 and J2-2 whilst the second electrode is connected to J2-3 and J2-4. The connections and types and values of the parts are shown on the Figure.
~-! Section 1 of Figure 3 forms an efficient step-down switched mode volta~e source and Section 2 forms a low j differential linear current source. The function of the ¦ switching regulator is to hold the current source differential voltage, TP14 to TP15, constant at 380mV thus maintaining low current source dissipation. The switched :~; WO94/~011 21~1617 PCT/GB93/01618 mode voltage source operates at approximately 72RHz and is based around a pulse width modulation control device t U4 type Tp494 .
A voltage of 380mV greater than the voltage at TPl5 is generated at- U4 pin 2 by the networ~ R27, Dll, DlO, Q4, R23, U3, R24, R25. This voltage is utilised to program the switched mode supply to issue an output voltage at TPl4 of TPl5 + 380mV thus maintaining 380mV differential from TPl4 to TPl5.
The controlled pulse width output from U4 pin 8 and ll drives the main switching mosfet Ql9 via buffer stage Q5 and Q6. Ql9 forms the switching element of a flybac~ step-: down configuration which consists of a flyback inductor L2, aback emf catch diode Dl5 and a storage capacitor C30.
. A voltage waveform representative of the tube arc current waveform and derived from R85 is fed to the RMS to DC
convertor (Section 4) via the sense + and sense - lines. The convertor is not a true RMS to DC conversion circuit but a ,quasi design which operates sastisfactorily provided that, as . in this case, the input waveshape and duty cycle are fixed.
The convertor operates by first of all buffering the signal via voltage follower U7 and removing front edge waveform overshoot via low pass filter R55/Cl9. The resulting waveform is then applied to the peak detector consisting of ,U6/Dl2/R37/C22 and R59 which results in a voltage being developed across C22 which is representative of the peak arc 'current. A voltage representative of the RMS arc current is then generated by passing the peak voltage via a buffer amp (USA) to a potential divider R33/R34 which attenuates the' ,signal by the arc,waveform duty cycle:factor (95% or X 0.95) resulting in a voltage representative of the RMS arc current at TP5.
- The integrating error amplifier (Section 3) compares the voltage representing achieved~RMS arc current at TP5 with a ~oltage representing the required RMS current which is formed by the RMS arc current selection header system (Section 6).' The header HDl allows the selection of any one WO94/0401l 14 PCT/GB93/01618 from eight possible potential dividers.
Both the achieved RMS arc current voltage and the re~uired RMS arc current voltage utilise a scaling f ~ctor of 1 volt DC = 1 Amp RMS of arc cur~ent.
The output from the error a~p~lsfier, USD pin 14, is used to program the current source (Section 2) which in turn issues a current to the arc trans,former primary which is stepped down by the arc transforme~ to form the arc current.
Section 7 is the arc transformer push-pull driver st~ge. U9 (an IP494) is a pulse width modulator driver IC
but configured to deliver a fixed push-pull duty cycle of 95%. The 95~ duty cycle resulting in 5~ dead time when neither push or pull drivers are active, ensures that there is no possibility of both push and pull drivers being energised simultaneously due to drive signal o~erlap. The push-pull signals originating from U9 pins 9 and 10 are buffered via Q15/16/17/18 and passed to the drive mosfets Q21 and Q22 which drive the two arc transformer primary windings.
Note that the two driving mosfets Q21 and QZ2 dri~e the primary windings in opposing phase to generate the push-pull operatsng mode. U9 operates at a frequency of 62 XHz as determined by l.l/R73 C24 which due to the push-pull drive nature ! results in an arc waveform of half this value ie 31KHz.
The electrode transformer push-pull drivers (Section 9) is of similar design to the arc transformer push-pull dri~er stage. This stage drives the electrode transformer ~Section 10) for approximately 1.5 seconds during the strike sequence after which it is inhibited. The operating frequency is 74KHz as determined by l.l/R71, ~23 which ! results in an electrode waveform frequency of 37KHz.
- Section 8 represents the strike oscillator the purpose of which is to charge strike capacitor C32 to approximately 91V. The oscillator is a simple flyback configuration with Ll forming the flyback inductor and operates at 65 to 85KHz.
The complete system is controlled and synchronised by WO94/04011 21 41~17 PCT/GB93/01618 the system controller (Section 5) which is reset on power-up by the pow~r-up reset circuit (Section 13).
The two phases of the strike sequence are represented - by the logic state of the P/S & R line (Prime, strike and run). With P/S & R in the high state, Phase 1 of the strike sequence is initiated with the electrode transformer push-I pull driver enabled via DPlC, the strike oscillator enabled due to Q11 being in the "off" state and the arc transformer push-pull driver being disabled due also to Qll being in the "off" state.
With P/S & R in the low state, Phase 2 of the strike sequence is initiated where the electrode transformer push-pull driver is disabled via DPlC, the strike oscillator is disabled due to Qll being in the "on" state and the arc transformer driver is enabled due also to Qll being in the i "on" state.
¦ By utilising a signal from the output error amplifier ! derived by Z2, R12, R16 and Q3, the control circuit is able to detect a tube strike failure and thus time a period by time constant R17/C8 during which multi-strike attempts are made via repeated cycling of Phase 1 and Phase 2 strike procedures. Failure to strike within this period results in a system shut-down by U2A pin 2 switching low into the "give up " state shutting down both electrode and arc drive waveform generators.
Values for the arc current set resistors R40 to R47 are selected such that six tubes may be catered for with two spare uncommitted tube ~ypes. The six tubes used in this example are 18W 2 foot (61cms), 30W 3 foot ~91.4cms), 36W 4 foot (121.9cms), 36WPL, 38W 31f2 foot (106.7 cms) and 40WPL.
The value of arc current selected for each tube results in a tube arc power which is 82% that of rated tube arc power. This provides a highly desirable combination of tube radiated heat, tube light output and system power consumption. The arc current may however be tailored to the requirements of the individual.
A suitable arc transformer design for the above tube 21 416 1~ `, ;` . .;; ~
W094/0401l 16 PCT/GB93/01618 range is given in Figure 4. The table below shows the required transformer ~ap selectlons made on the arc transformer tape selection header and the corresponding RMS
arc current values selected via the RMS arc current selection header resulting in 82% of rated arc power.
On comparative test run using a driver D in accordance with the invention as disclosed herein and a 36W
rated tube, run at a total tube power of 29.5W, as compared with a known system C run at 50Hz mains voltage and at the 36W rated arc power, with ambient temperature of 21C to 22.5C, gave the following results.
Total Tube Power Light Output Tl T2 T3 Hottest % of Mains Component .
Temperature C 36W 100 4319.3 19.3 ~ 53.0 (Ballast~
D 29.5W 87 2415.2 15.2 17.0 (Heatsink) ,.
Where Tl, T2, T3 are all temperatures in degrees centigrade ! above ambient temperature respectively taken at-the tube electrodes r one quarter of the tube length from the electrodes, and midpoint of the tube.
.
_ .
Tube TypeRMS Arc Current fsrRequired Transformer 82% Rated Arc Power Tap Pin Number . . ' 18W 6lcms 25OmA 10 30W 91.4cms250mA 11 36W 121.9cms275mA 11 36WPL 285mA 11 38W 106.7cms285mA 11 40WPL 230mA 12 214161q'-'' A design for ~he electrode transformer is shown in Figure 5.
Both transformers are ~ased around Philips RMlO
formers. In order to ob~ain a high arc transformer operating efficiency, a low lo~s ferrite material should be utilised.
As the arc transformer operates at 32KHz, a suitable low loss ferrite at this frequency is either Philips 3C85 ungapped or Siemens N41 ungapped. The design shown in Figure 4 operates at 170 to 230mT (Milli-Teslas) which ensures freedom from magnetic saturation. A similar srade of ferrite may be utilised for the electrode transformer.
Figure 4 shows the transformer bobbin and pins for forming the arc transformer 22. The windings are not shown but all the primaries are wound in the same direction and all the secondaries are wound in the same direction. The bobbin is a Philips 43220Q21-34060 with 12 pins. The windings are as follows:
First primary, -12 turns, 0.75 millimetre diameter ECW
Second primary, 12 turns, 0.75 millimetre diameter ECW
First secondary, 48 turns, 0.375 millimetre diameter ECW
Second secondary, 12 turns, 0.375 millimetre diameter ECW
'- Third secondary, 24 turns, 0.375 millimetre diameter ECW
Fourth secondary, 26 turns, 0.375 millimetre diameter ECW.
The first primary starts at pin l and finishes at pin
The electrode pre-heat system consists of a push-pull step down transformer configuration generating two galvanically isolated electrode pre-heat voltages.
During phase one which is of approximately l.5 seconds duration, the main arc transformer push-pull drive system is disabled.
During phase two, the strike oscillator and th~
electrode pre-heat system are disabled and the arc transformer push-pull drive is enabled. Initially, drive to the arc transformer results in the voltage across Cs being stepped up by the transformer ratio. This results in the generation of a high potential across the tube arc resulting ln a tube strike. The result is a decaying alternating voltage across the tube arc as the strike capacitor discharges.
During initial strike period, a current flow is established into the tube arc which has the effect of activating the sys~em arc current control loop.
Current flowing to the arc results in an alternating arc current wave form across Rs, a measure of which is passed to the RMS to DC convertor 33, the outpu~ from which is a DC
voltage proportional to the RMS tube arc current. The voltage from the RMS output is ~ompared in the error amplifier 35, to a selected programme voltage (at input 39) representing the desired tube RMS arc current. The amplifier output (error signal) on line 40 is utilised to programme the linear low differential current source 41, the resulting output from which is fed to the arc transformer primary winding.
The current flow in the primary winding is stepped down by the transformer ratio to produce an arc current which, in a matter of milliseconds, is adjusted to the value set at the error amplifier programme input 39, by nature of the arc current feedback taken from Rs (as described). This I
?rovides a closed 'oop servo control system maintaining substantially constant the t~be arc current by varying the amplitude of the arc curr~ent waveform.
The net effect is that the tube strike is initiated by the discharge of the strike capacitor but maintained by the arc cuxrent control loop. By nature of the fact that the tube volt/ampere characteristic is fixed, the desired arc current results in a fixed arc power.
If the tube arc fails to strike on application of the stri.~e ~oltage, then a signal from the output of the error amplifier, on line 57, which signal is indicative of a strike failure, is utilised to force the system control circuit to re-e~ter the phase l of the strike procedure and thus restart the strike sequence.
Repetitive strike failure is measured by the give up circuitry 52, which after a predetermined period corresponding to a predetermined number of failures commands a system shut down on line 56, whereby both the electrode and arc drive systems are disabled. This action will occur after approximately 6 to 8 strike attempts or approximately 25 seconds.
The arc transformer programmable current source 41 is of t inear design and is designed to operate at low differential voltages to attain low dissipation. As the output voltage V2 from this current source will be determined by the tube arc voltage as set by the transformer ratio (V2 is typically about 18 volts), and the current source differential will be hundreds of millivolts tVl minus V2 is typically about 0.38 volts), the switched mode power supply 44 is employed to efficiently reduce the 22 to 33 volt ~nominal 24 volts) supply 15 to the voltage attained at Vl.
The switched mode power supply unit monitors the current source differential voltage ~Vl-V2) and holds this ~alue constant irrespective of the voltage of V2 dictated by the tube.
~ t is important to realise that the current source 41 is programmed by the error amplifier 35 and the switched 214161~
WO94/04011 ll PCT/GB93/01618 mode ~ower supply 44 is programmed from the curren~ source in that order.
The ratio- of the arc transformer is selec~ed such that Vp is placed in ~he optimum operating range of 13 to 18 volts.
, The arc transformer push-pull driver 24 is chosen to produce a 90 to 95 per cent duty cycle, symmetrical arc voltage wave form of a frequency 32 KHz nominal. An example of an arc voltage wave form and resulting arc current wave form plot~ed against time, as achieved by the Figure l circ~it is shown in Figure 2. The fixed duty cycle of 90 to 95 per cent, attains the low arc current crest factor of typically l~3 to l.5 dependent on the tube type. The wave form has sharply defined on off characteristics.
The electrode drive push-pull system results in the production of two electrode drive voltages which a~ain are symmetrical and of frequency 36 KHz nominal.
This system is designed to cope with a wide range of standard "off the shelf" tubes and for this purpose it has j the ability to deliver tube arc powers of between lO and 40 watts and is quickly configurable to the desired tube style I by the appropriate placement of the two printed circuit style jumper links 38 and 28 which are used to select tube arc current and tube arc voltage. For example, eight dividers : may be provided for generating the arc current prsgramme ~oltages required for six popular tubes with provision for two spares and four arc transformer tap sele~tion positions are provided in the unit 28. By utilisation of the jumper link selection sys~em, it is possible to select the tube type within seconds. The first selection is used to select one of the number of resistor pairs in the unit 38 which determine the tube arc current. The second selection is used to select one of a number of taps (for example four) from the transformer driving tube arc in the system 28. This second selection is necessary in order to ensure compliance with the tube operating arc voltage. In the circuit described six tubes are catered for with two spare uncommitted tube types.
¦ W094/0401l 2 1 41 6 17 12 PCT/GB93/01618 The six tubes are 18 watt two foot (61cms), 30 watt three foot (91.4cms), 36 watt four foot (121.9cms), 36wp1, 38 watt three foot six inches (106.7cms) and 40wpl. It should be emphasised however that the design is capable of dri~ing any tubes within the range 10 to 40 watts~nd is by no means limited to the above types. ;;~.
Figure 3 shows the implement~ation of the described system which may be related to the block diagram of Figure 1 by reference to the following circuit section descriptions.
Section 1 Switched mode voltage source Section 2 Low differential current source Section 3 Integrating Error ~mplifier Section 4 ~MS to the DC con~ertor Section 5 System control Section 6 RMS arc current selection header and resistors Section 7 Arc transformer push-pull driver - Section 8 Strike oscillator Section 9 Electrode transformer push-pull dri~er Section 10 Electrode transformer Section 11 Ar~ transformer Section 12 Arc transformer tap selection Section 13 Power-up reset circuit Section 14 Short circuit/overload shut-down - With reference to Fiyure 3, the 24 volt nominal DC
supply is applied to Jl-l(+VE) and Jl-3(0V). Dl provides protection from reverse connection of the 24 volt supply.
The four terminal connection to the tube is made at J2. One electrode should be connected to J2-1 and J2-2 whilst the second electrode is connected to J2-3 and J2-4. The connections and types and values of the parts are shown on the Figure.
~-! Section 1 of Figure 3 forms an efficient step-down switched mode volta~e source and Section 2 forms a low j differential linear current source. The function of the ¦ switching regulator is to hold the current source differential voltage, TP14 to TP15, constant at 380mV thus maintaining low current source dissipation. The switched :~; WO94/~011 21~1617 PCT/GB93/01618 mode voltage source operates at approximately 72RHz and is based around a pulse width modulation control device t U4 type Tp494 .
A voltage of 380mV greater than the voltage at TPl5 is generated at- U4 pin 2 by the networ~ R27, Dll, DlO, Q4, R23, U3, R24, R25. This voltage is utilised to program the switched mode supply to issue an output voltage at TPl4 of TPl5 + 380mV thus maintaining 380mV differential from TPl4 to TPl5.
The controlled pulse width output from U4 pin 8 and ll drives the main switching mosfet Ql9 via buffer stage Q5 and Q6. Ql9 forms the switching element of a flybac~ step-: down configuration which consists of a flyback inductor L2, aback emf catch diode Dl5 and a storage capacitor C30.
. A voltage waveform representative of the tube arc current waveform and derived from R85 is fed to the RMS to DC
convertor (Section 4) via the sense + and sense - lines. The convertor is not a true RMS to DC conversion circuit but a ,quasi design which operates sastisfactorily provided that, as . in this case, the input waveshape and duty cycle are fixed.
The convertor operates by first of all buffering the signal via voltage follower U7 and removing front edge waveform overshoot via low pass filter R55/Cl9. The resulting waveform is then applied to the peak detector consisting of ,U6/Dl2/R37/C22 and R59 which results in a voltage being developed across C22 which is representative of the peak arc 'current. A voltage representative of the RMS arc current is then generated by passing the peak voltage via a buffer amp (USA) to a potential divider R33/R34 which attenuates the' ,signal by the arc,waveform duty cycle:factor (95% or X 0.95) resulting in a voltage representative of the RMS arc current at TP5.
- The integrating error amplifier (Section 3) compares the voltage representing achieved~RMS arc current at TP5 with a ~oltage representing the required RMS current which is formed by the RMS arc current selection header system (Section 6).' The header HDl allows the selection of any one WO94/0401l 14 PCT/GB93/01618 from eight possible potential dividers.
Both the achieved RMS arc current voltage and the re~uired RMS arc current voltage utilise a scaling f ~ctor of 1 volt DC = 1 Amp RMS of arc cur~ent.
The output from the error a~p~lsfier, USD pin 14, is used to program the current source (Section 2) which in turn issues a current to the arc trans,former primary which is stepped down by the arc transforme~ to form the arc current.
Section 7 is the arc transformer push-pull driver st~ge. U9 (an IP494) is a pulse width modulator driver IC
but configured to deliver a fixed push-pull duty cycle of 95%. The 95~ duty cycle resulting in 5~ dead time when neither push or pull drivers are active, ensures that there is no possibility of both push and pull drivers being energised simultaneously due to drive signal o~erlap. The push-pull signals originating from U9 pins 9 and 10 are buffered via Q15/16/17/18 and passed to the drive mosfets Q21 and Q22 which drive the two arc transformer primary windings.
Note that the two driving mosfets Q21 and QZ2 dri~e the primary windings in opposing phase to generate the push-pull operatsng mode. U9 operates at a frequency of 62 XHz as determined by l.l/R73 C24 which due to the push-pull drive nature ! results in an arc waveform of half this value ie 31KHz.
The electrode transformer push-pull drivers (Section 9) is of similar design to the arc transformer push-pull dri~er stage. This stage drives the electrode transformer ~Section 10) for approximately 1.5 seconds during the strike sequence after which it is inhibited. The operating frequency is 74KHz as determined by l.l/R71, ~23 which ! results in an electrode waveform frequency of 37KHz.
- Section 8 represents the strike oscillator the purpose of which is to charge strike capacitor C32 to approximately 91V. The oscillator is a simple flyback configuration with Ll forming the flyback inductor and operates at 65 to 85KHz.
The complete system is controlled and synchronised by WO94/04011 21 41~17 PCT/GB93/01618 the system controller (Section 5) which is reset on power-up by the pow~r-up reset circuit (Section 13).
The two phases of the strike sequence are represented - by the logic state of the P/S & R line (Prime, strike and run). With P/S & R in the high state, Phase 1 of the strike sequence is initiated with the electrode transformer push-I pull driver enabled via DPlC, the strike oscillator enabled due to Q11 being in the "off" state and the arc transformer push-pull driver being disabled due also to Qll being in the "off" state.
With P/S & R in the low state, Phase 2 of the strike sequence is initiated where the electrode transformer push-pull driver is disabled via DPlC, the strike oscillator is disabled due to Qll being in the "on" state and the arc transformer driver is enabled due also to Qll being in the i "on" state.
¦ By utilising a signal from the output error amplifier ! derived by Z2, R12, R16 and Q3, the control circuit is able to detect a tube strike failure and thus time a period by time constant R17/C8 during which multi-strike attempts are made via repeated cycling of Phase 1 and Phase 2 strike procedures. Failure to strike within this period results in a system shut-down by U2A pin 2 switching low into the "give up " state shutting down both electrode and arc drive waveform generators.
Values for the arc current set resistors R40 to R47 are selected such that six tubes may be catered for with two spare uncommitted tube ~ypes. The six tubes used in this example are 18W 2 foot (61cms), 30W 3 foot ~91.4cms), 36W 4 foot (121.9cms), 36WPL, 38W 31f2 foot (106.7 cms) and 40WPL.
The value of arc current selected for each tube results in a tube arc power which is 82% that of rated tube arc power. This provides a highly desirable combination of tube radiated heat, tube light output and system power consumption. The arc current may however be tailored to the requirements of the individual.
A suitable arc transformer design for the above tube 21 416 1~ `, ;` . .;; ~
W094/0401l 16 PCT/GB93/01618 range is given in Figure 4. The table below shows the required transformer ~ap selectlons made on the arc transformer tape selection header and the corresponding RMS
arc current values selected via the RMS arc current selection header resulting in 82% of rated arc power.
On comparative test run using a driver D in accordance with the invention as disclosed herein and a 36W
rated tube, run at a total tube power of 29.5W, as compared with a known system C run at 50Hz mains voltage and at the 36W rated arc power, with ambient temperature of 21C to 22.5C, gave the following results.
Total Tube Power Light Output Tl T2 T3 Hottest % of Mains Component .
Temperature C 36W 100 4319.3 19.3 ~ 53.0 (Ballast~
D 29.5W 87 2415.2 15.2 17.0 (Heatsink) ,.
Where Tl, T2, T3 are all temperatures in degrees centigrade ! above ambient temperature respectively taken at-the tube electrodes r one quarter of the tube length from the electrodes, and midpoint of the tube.
.
_ .
Tube TypeRMS Arc Current fsrRequired Transformer 82% Rated Arc Power Tap Pin Number . . ' 18W 6lcms 25OmA 10 30W 91.4cms250mA 11 36W 121.9cms275mA 11 36WPL 285mA 11 38W 106.7cms285mA 11 40WPL 230mA 12 214161q'-'' A design for ~he electrode transformer is shown in Figure 5.
Both transformers are ~ased around Philips RMlO
formers. In order to ob~ain a high arc transformer operating efficiency, a low lo~s ferrite material should be utilised.
As the arc transformer operates at 32KHz, a suitable low loss ferrite at this frequency is either Philips 3C85 ungapped or Siemens N41 ungapped. The design shown in Figure 4 operates at 170 to 230mT (Milli-Teslas) which ensures freedom from magnetic saturation. A similar srade of ferrite may be utilised for the electrode transformer.
Figure 4 shows the transformer bobbin and pins for forming the arc transformer 22. The windings are not shown but all the primaries are wound in the same direction and all the secondaries are wound in the same direction. The bobbin is a Philips 43220Q21-34060 with 12 pins. The windings are as follows:
First primary, -12 turns, 0.75 millimetre diameter ECW
Second primary, 12 turns, 0.75 millimetre diameter ECW
First secondary, 48 turns, 0.375 millimetre diameter ECW
Second secondary, 12 turns, 0.375 millimetre diameter ECW
'- Third secondary, 24 turns, 0.375 millimetre diameter ECW
Fourth secondary, 26 turns, 0.375 millimetre diameter ECW.
The first primary starts at pin l and finishes at pin
3, the second primary starts at pin 4 and finishes at pin 6, the first secondary starts at pin 7 and finishes at pin 9, the secondary starts at pin 9 and finishes at pin lO, the third secondary starts a~ pin lO and finishes at pin ll and the fourth secondary starts at pin ll and finishes at pin 12.
The primaries must be put on to the bobbin first and interwinding tape should be used between the primaries and secondaries and between secondary one and secondary two and over the outside.
Figure 5 shows the transformer bobbin and pins for the electrode ~ransformer 17. The bobbin is a Philips 4322-021-34730 with 12 pins and all windings are in the same wo 94/04011 18 PCI`/GB93/01618 direction and made fr..o~ ,0.-4 millimetre diameter wixe.
Winding l s~arts at pin 10, has 48 turns and finishes at pin 3~ .
Winding 2 starts at pin 12, has 48 turns and finishe at pin 1.
Winding 3 starts at pin 4, has 12 turns and finishes at pin 9.
Winding 4 s~arts at pin 6, has 12 turns and finishes at Din 7.
Insulating tape rated at 80C continuous should be used between each winding and on the external winding.
- It should be emphasised that the design shown is capable of dri~ing any tube in the range 10 to 40 watts and is by no means limited to the above selection. It can be adapted to operate tubes of higher voltage. All that is required to tailor the system to a specific tube is the correct selection of the RMS arc current program voltage and correct design of the arc transformer winding.
If the arc transformer is required to be- modified in order to comply with a speci~ic tube not mentioned, then one should retain the same primary winding as Figure 4, but select the secondary winding such that TP7 (the primary tap) r~ is placed r at approximately 17.5 volts with the RMS tube voltage at the desired value.
If VT = RMS voltage of tube at desired tube power D = Du~y Cycle of drive = 0.95 VTP7 Voltage at TP7 = 17O5V
NS = Number of secondary turns Np - Number of primary turns = 12 Then NS = VTNp x 1 VTp7 D
i If the RMS arc current is required to be modified to a value not available from the existing values, then a spare i, W094/04011 l9 PCT/GB93/01618 resistor/header ~osi~ion should be utilised to set the desired arc current progr~m voltage ie R41 and the value for R4l calculated as follows:
If R4l Value of R4l V = Voltage representing RMS arG current 1 VDC = lV R~S of arc current R6l Value of R6l = 2Ok R4l 6l (15/V-l) While one embodiment of the system has been described in detail for use with a low voltage 24 volt nominal source, the concepts can be applied to a system run from other voltages or from any conventional mains voltage source converted to produce a DC voltage supply, and with -`
appropriate change of component values.
The primaries must be put on to the bobbin first and interwinding tape should be used between the primaries and secondaries and between secondary one and secondary two and over the outside.
Figure 5 shows the transformer bobbin and pins for the electrode ~ransformer 17. The bobbin is a Philips 4322-021-34730 with 12 pins and all windings are in the same wo 94/04011 18 PCI`/GB93/01618 direction and made fr..o~ ,0.-4 millimetre diameter wixe.
Winding l s~arts at pin 10, has 48 turns and finishes at pin 3~ .
Winding 2 starts at pin 12, has 48 turns and finishe at pin 1.
Winding 3 starts at pin 4, has 12 turns and finishes at pin 9.
Winding 4 s~arts at pin 6, has 12 turns and finishes at Din 7.
Insulating tape rated at 80C continuous should be used between each winding and on the external winding.
- It should be emphasised that the design shown is capable of dri~ing any tube in the range 10 to 40 watts and is by no means limited to the above selection. It can be adapted to operate tubes of higher voltage. All that is required to tailor the system to a specific tube is the correct selection of the RMS arc current program voltage and correct design of the arc transformer winding.
If the arc transformer is required to be- modified in order to comply with a speci~ic tube not mentioned, then one should retain the same primary winding as Figure 4, but select the secondary winding such that TP7 (the primary tap) r~ is placed r at approximately 17.5 volts with the RMS tube voltage at the desired value.
If VT = RMS voltage of tube at desired tube power D = Du~y Cycle of drive = 0.95 VTP7 Voltage at TP7 = 17O5V
NS = Number of secondary turns Np - Number of primary turns = 12 Then NS = VTNp x 1 VTp7 D
i If the RMS arc current is required to be modified to a value not available from the existing values, then a spare i, W094/04011 l9 PCT/GB93/01618 resistor/header ~osi~ion should be utilised to set the desired arc current progr~m voltage ie R41 and the value for R4l calculated as follows:
If R4l Value of R4l V = Voltage representing RMS arG current 1 VDC = lV R~S of arc current R6l Value of R6l = 2Ok R4l 6l (15/V-l) While one embodiment of the system has been described in detail for use with a low voltage 24 volt nominal source, the concepts can be applied to a system run from other voltages or from any conventional mains voltage source converted to produce a DC voltage supply, and with -`
appropriate change of component values.
Claims (14)
1 A fluorescent tube driver arranged to be supplied by a voltage source (15) and having a tube driver output with a frequency of oscillation in the range 15 to 50 KHz, the driver comprising an arc waveform transformer (22), the primary winding (23) of which is supplied with a variable drive current with sharply defined on/off characteristics derived from the voltage source, and the secondary winding (25) of which is adapted to the connected to the electrodes (13, 14) of a fluorescent tube (12), such that in use an alternating tube arc current (Figure 2) will flow through the secondary winding and tube, and including a closed loop control system (31-44) characterised in that the closed loop control system (31-44) comprises means (31-34) for measuring the arc current flowing through the secondary winding and tube to produce a measured signal representing actual arc current supply, means (36-38) for generating a reference signal representing desired arc current, comparator means (35) for comparing the measured signal and the reference signal and producing an error signal, and a drive current adjustment means (39-44) responsive to the error signal to adjust so as to maintain constant the drive current (I) at the level selected and without change to drive waveform frequency or duty cycle, whereby the amplitude of the arc current and the arc current crest factor are maintained constant.
2 A driver according to claim 1 characterised in that the voltage. source is a low voltage source (less than 50 volts nominal).
3 A driver according to claim 2 characterised in that the low voltage source is a 24 volt nominal supply.
4 A driver according to any of claims 1 to 3 characterised in that the frequency of oscillation is substantially 32 KHz nominal.
A driver. according to any of claims 1 to 4 characterised in that the arc current is selected for a particular tube such that the tube arc power is less than 90 per cent of the rated tube power.
6 A driver according to any of claims 1 to 5 characterised by an arc transformer push/pull driver (24) for the arc transformer, which driver is selected to give a symmetrical arc wave form having the substantially constant wave form duty cycle.
7 A driver according to claim 6 characterised in that the duty cycle is in the range 90 to 95 per cent.
8 A driver according to claim 6 or claim 7 characterised in that it is arranged, for any particular tube setting, to maintain the constant value of the arc crest factor in the range 1.3 to 1.5.
9 A driver according to any of claims 1 to 8 characterised in that the arc current flow circuit includes no dissipating device forming an arc current limiting element.
A driver according to any of claims 1 to characterised in that the secondary winding (25) of the arc transformer is arranged to be connected to the fluorescent tube (12) from a selected one of a plurality of tap points on the secondary winding and the selection of the tap point is by a jumper line selection system (28).
11 A driver according to any of claims 1 to 10 characterised is that the drive voltage adjustment means comprises a low differential current source unit (41) having a voltage output V2 and switched mode power supply unit (44) arranged to receive the supply voltage V and having an output voltage of V1 arranged to be supplied to the low differential current supply unit, the outputs V2 and V1 being measured by the switched mode supply unit which is arranged to hold the current source differential V2 minus V1 constant.
12 A driver according to claim 11 characterised in that the current source unit (41) is programmed by the error signal and the switched mode supply unit (44) is programmed from the current source unit in that order.
13 A driver according to any of claims 1 to 12 including a strike oscillator (47) arranged at start up to supply a strike voltage to the tube arc, which voltage is higher than the formal running arc voltage, characterised by means (50, 51, 57) for detecting whether or not a strike has occurred and arranged to initiate a re-strike attempt if an attempted strike has failed, and means (52) arranged to initiate shut down after a predetermined number of strike attempts or a predetermined time period.
14 A circuit according to claims 13 characterised by means (57) adapted to detect removal or failure of a tube and to reinitiate multi-strike attempts.
A lighting system including a tube driven by a driver according to any of the preceding claims.
A lighting system including a tube driven by a driver according to any of the preceding claims.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9216425A GB2269279A (en) | 1992-08-01 | 1992-08-01 | Fluorescent Tube Starting and Operating Circuit |
| GB9216425.0 | 1992-08-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2141617A1 true CA2141617A1 (en) | 1994-02-17 |
Family
ID=10719716
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2141617 Abandoned CA2141617A1 (en) | 1992-08-01 | 1993-07-30 | Florescent tube driver and lighting system |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0653150A1 (en) |
| AU (1) | AU4719493A (en) |
| CA (1) | CA2141617A1 (en) |
| GB (1) | GB2269279A (en) |
| WO (1) | WO1994004011A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0642296A3 (en) * | 1993-09-08 | 1995-07-26 | Smi Syst Microelect Innovat | Process for detecting a faulty fluorescent lamp operated by high-frequency. |
| JP3279476B2 (en) * | 1996-04-18 | 2002-04-30 | 株式会社小糸製作所 | Lighting device for discharge lamp |
| AU1755699A (en) * | 1997-12-23 | 1999-07-19 | Tridonic Bauelemente Gmbh | Electronic lamp ballast |
| WO2002060228A1 (en) | 2001-01-24 | 2002-08-01 | Stmicroelectronics S.R.L. | Fault management method for electronic ballast |
| US6864642B2 (en) * | 2002-10-07 | 2005-03-08 | Bruce Industries, Inc. | Electronic ballast with DC output flyback converter |
| EP2914715A1 (en) * | 2012-11-05 | 2015-09-09 | Osram Sylvania Inc. | Driver for solid state light sources |
| CN113475166A (en) | 2019-02-25 | 2021-10-01 | 普利莫宗产品公司 | Low-frequency ozone generator |
Family Cites Families (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB898580A (en) * | 1959-08-21 | 1962-06-14 | Gen Electric Co Ltd | Improvements in or relating to circuit arrangements for operating low pressure electric discharge lamps |
| BE786136A (en) * | 1971-07-13 | 1973-01-11 | Philips Nv | DEVICE FOR FEEDING AT LEAST ONE GAS AND / OR VAPOR DISCHARGE LAMP |
| US3969652A (en) * | 1974-01-04 | 1976-07-13 | General Electric Company | Electronic ballast for gaseous discharge lamps |
| FR2416617A1 (en) * | 1978-02-07 | 1979-08-31 | Signaux Entr Electriques | CONVERTER FOR THE POWER SUPPLY OF DISCHARGE LAMPS, AND MORE GENERALLY OF ARC LAMPS, AND ITS APPLICATION TO PROJECTORS FOR SUCH LAMPS |
| US4277728A (en) * | 1978-05-08 | 1981-07-07 | Stevens Luminoptics | Power supply for a high intensity discharge or fluorescent lamp |
| US4375608A (en) * | 1980-05-30 | 1983-03-01 | Beatrice Foods Co. | Electronic fluorescent lamp ballast |
| US4723098A (en) * | 1980-10-07 | 1988-02-02 | Thomas Industries, Inc. | Electronic ballast circuit for fluorescent lamps |
| US4370600A (en) * | 1980-11-26 | 1983-01-25 | Honeywell Inc. | Two-wire electronic dimming ballast for fluorescent lamps |
| GB2095930A (en) * | 1981-03-27 | 1982-10-06 | Stevens Carlile R | Constant power ballast |
| US4385262A (en) * | 1981-11-30 | 1983-05-24 | International Business Machines Corporation | Method and apparatus for variable current control of a negative resistance device such as a fluorescent lamp |
| US4644228A (en) * | 1985-01-14 | 1987-02-17 | Nilssen Ole K | Series-resonant parallel-loaded fluorescent lamp ballast |
| US5015923A (en) * | 1986-09-15 | 1991-05-14 | Nilssen Ole K | Extra efficient electronic ballast for fluorescent lamps |
| US4862040A (en) * | 1987-03-18 | 1989-08-29 | Nilssen Ole K | Frequency-modulated inverter-type ballast |
| US5041766A (en) * | 1987-08-03 | 1991-08-20 | Ole K. Nilssen | Power-factor-controlled electronic ballast |
| GB2212995A (en) * | 1987-10-23 | 1989-08-02 | Rockwell International Corp | Fluorescent lamp dimmer |
| GB8822195D0 (en) * | 1988-09-21 | 1988-10-26 | W J Parry Nottm Ltd | Improvements in/related to electronic ballast circuits |
| US4958108A (en) * | 1989-02-14 | 1990-09-18 | Avtech Corporation | Universal fluorescent lamp ballast |
| IT8967903A0 (en) * | 1989-10-20 | 1989-10-20 | Marelli Autronica | POWER SUPPLY DEVICE FOR GAS DISCHARGE LAMPS FOR USE ON BOARD MOTOR VEHICLES. |
| EP0439861A1 (en) * | 1990-01-29 | 1991-08-07 | Koninklijke Philips Electronics N.V. | Circuit arrangement |
| GB2244608A (en) * | 1990-04-23 | 1991-12-04 | P I Electronics Pte Ltd | High frequency drive circuit for a fluorescent lamp |
| US5089753A (en) * | 1990-07-09 | 1992-02-18 | North American Philips Corporation | Arrangement for predicting failure in fluorescent lamp systems |
| DE4039498B4 (en) * | 1990-07-13 | 2006-06-29 | Lutron Electronics Co., Inc. | Circuit and method for dimming gas discharge lamps |
| US5055746A (en) * | 1990-08-13 | 1991-10-08 | Electronic Ballast Technology, Incorporated | Remote control of fluorescent lamp ballast using power flow interruption coding with means to maintain filament voltage substantially constant as the lamp voltage decreases |
-
1992
- 1992-08-01 GB GB9216425A patent/GB2269279A/en not_active Withdrawn
-
1993
- 1993-07-30 AU AU47194/93A patent/AU4719493A/en not_active Abandoned
- 1993-07-30 CA CA 2141617 patent/CA2141617A1/en not_active Abandoned
- 1993-07-30 EP EP93917958A patent/EP0653150A1/en not_active Withdrawn
- 1993-07-30 WO PCT/GB1993/001618 patent/WO1994004011A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| AU4719493A (en) | 1994-03-03 |
| GB2269279A (en) | 1994-02-02 |
| EP0653150A1 (en) | 1995-05-17 |
| WO1994004011A1 (en) | 1994-02-17 |
| GB9216425D0 (en) | 1992-09-16 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Dead |