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
  • H05B41/282—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
  • H05B41/2825—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 by means of a bridge converter in the final stage
  • H05B41/2828—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 by means of a bridge converter in the final stage using control circuits for the switching elements
• • 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
  • H05B41/36—Controlling
  • H05B41/38—Controlling the intensity of light
  • H05B41/39—Controlling the intensity of light continuously
  • H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
  • H05B41/3921—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations
• • 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
  • H05B41/36—Controlling
  • H05B41/38—Controlling the intensity of light
  • H05B41/39—Controlling the intensity of light continuously
  • H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
  • H05B41/3921—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations
  • H05B41/3927—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations by pulse width modulation

Definitions

• the present invention relates to an electronic ballast with a full bridge circuit for controlling the operating behavior and the brightness of a gas discharge lamp according to the preamble of claim 1 and a method for controlling the brightness of a gas discharge lamp.
• Electronic ballasts with full-bridge circuits are preferably used to operate high-pressure gas discharge lamps, but are also used for low-pressure discharge lamps or fluorescent tubes.
• the use of a bridge circuit enables the lamps to be operated with a direct current, which may be reversed with a low frequency, which can reduce the occurrence of disturbing electromagnetic alternating fields. Furthermore, in this case, the influence of the lamp wiring on the operation resulting from the high-frequency line impedances is negligible.
• Ballasts with full bridge circuits are described for example in DE 44 01 630 AI or AT 392 384 B.
• Switches S1 to S4 which are field effect transistors in the present example, are formed, the two first switches Slund S2 forming a first half bridge and the two switches S3 and S4 forming a second half bridge.
• a series resonance circuit consisting of an inductance L and a capacitance C is arranged, i.e. the series connection of the inductance L and the capacitor C connects the common node between the two switches S1 and S2 of the first half bridge with the common one
• the gas discharge lamp LA is arranged in parallel with the capacitor C.
• the input of the bridge circuit is fed with a direct voltage U BUS , which
• the output of the bridge circuit is connected to ground via a resistor R.
• the four switches S1 to S4 are controlled by two driver circuits T1 and T2, to which the corresponding control commands for controlling the switches S1 to S4 are in turn transmitted by a control circuit 6.
• the four switches S1 to S4 are generally activated in the following way: first, the switches S1 and S4 forming a first bridge diagonal are activated in a first phase, while the two switches S3 and S2 forming the second bridge diagonal are opened. In this first phase there is a current flow from the input of the VoUbruckensciens via the first switch, the load circuit consisting of the series resonance circuit and the gas discharge lamp LA and the switch S4.
• One of the two switches, for example switch S1 is closed permanently while switch S4 is clocked at high frequency.
• switches S1 and S4 of the first bridge diagonal are then opened, while switches S3 and S2 of the second bridge diagonal are now activated in an analogous manner, ie switch S3 is permanently closed, while switch S2 corresponds to the desired power Duty cycle clocks at high frequency.
• the change between the two diagonals of the bridge has the result that the direction of the current through the lamp LA changes permanently, thereby avoiding mercury deposits on an electrode and increasing the life of the lamp.
• control circuit 6 which is supplied on the one hand with a desired value I S0LL corresponding to the desired lamp brightness and on the other hand with the voltage dropping via the shunt resistor R via the input line 7 as an actual value.
• control circuit 6 generates control commands which are fed via lines 8 t to 8 4 to the two driver circuits T1 and T2, which in turn convert the control commands into corresponding signals for controlling the gates of the four field effect transistors S1 to S4.
• the clocked switch of the active bridge diagonals is opened and closed with a frequency of approx. 20 to 50 kHz. Due to this high-frequency clocking, parasitic currents flow across the lamp line capacitances, which make precise regulation of the lamp brightness impossible, in particular at very low dimming values, with the result that, at very low dimming values, an undesirable flickering of the lamp brightness occurs which is noticeable to the eye.
• the object is achieved by an electronic ballast which has the features of claim 1 and by methods for controlling the brightness of a gas discharge lamp according to claims 11 and 13.
• the electronic ballast according to the invention has a bridge circuit fed with a direct voltage, the gas discharge lamp being the load of the latter VoUbruckenscrien is switched.
• a control circuit alternately switches on a bridge diagonal of the bridge circuit and the other diagonal off.
• the two bridge diagonals each have a controllable constant current source for regulating the lamp current. In this case, high-frequency clocking of a switch can be dispensed with while a diagonal bridge is switched on.
• the lamp is operated with a regulated direct current during the on-time of a bridge diagonal, which avoids the problem of parasitic currents due to the high-frequency switching processes. This ensures that even at very low brightness values can be controlled very precisely to a constant lamp current and thus flickering of the lamp is suppressed.
• the low-frequency switching between the two diagonals of the bridge is maintained and is preferably carried out at a frequency of more than 100 Hz, that is to say at a frequency above the threshold of perception of the human eye, in particular at a frequency between 700 Hz and 2000 Hz a lamp operation at very low brightness to avoid switching between the two diagonals of the bridge, since the mercury migration caused by the small lamp current is minimal and is compensated for by the natural diffusion taking place in the lamp plasma.
• the ballast according to the invention therefore has a controllable smoothing circuit for generating a variable DC voltage supplied to the bridge circuit.
• a control circuit is provided which detects the voltage drop across the controllable constant current source of the respective active bridge diagonals and controls the smoothing circuit in such a way that this detected voltage essentially corresponds to a predetermined desired value.
• the smoothing circuit can consist of two switching regulators connected in series, the first switching regulator preferably being a step-up converter and the second switching regulator preferably being a step-down converter.
• the control circuit only controls the buck converter in the desired manner.
• the smoothing circuit can also be formed by a buck boost converter controlled by the control circuit.
• a second preferred exemplary embodiment of the electronic ballast according to the invention is that the gas discharge lamp is part of a resonance circuit connected as a load of the bridge circuit.
• a first operating mode which is used at low lamp brightness
• the lamp current is regulated as described above by the two controllable constant current sources of the bridge diagonals, the inductance not being effective in this case due to the direct current, but only its ohmic direct current resistance.
• a second operating mode when the lamp brightness is high, the power supplied to the lamp is controlled by changing the pulse duty factor at a constant high frequency. This means that in this second operating mode, the regulation of the lamp current is suppressed by the controllable constant current sources and the switches are clocked again. In this case, it is not necessary for the DC voltage supplied by the smoothing circuit of the bridge circuit to be regulated, since the controllable DC voltage is only used for the lower lamp brightnesses, but here the losses play a minor role anyway due to the low current intensities.
• the gas discharge lamp is basically operated with a regulated DC voltage during the on-time of a bridge diagonal.
• the two operating modes are used, the gas discharge lamp being operated in the first operating mode with low lamp brightness with a regulated direct voltage and in a second operating mode with high lamp brightness with a direct current corresponding to the pulse duty factor with superimposed ripple current.
• FIG. 1 shows a first embodiment of a bridge circuit according to the invention
• FIG. 2 shows a block diagram of a first ballast in which the bridge circuit shown in FIG. 1 is used
• Fig. 3 is a block diagram of a second ballast in which the bridge circuit shown in Fig. 1 is used;
• FIG. 4 shows a second exemplary embodiment of a bridge circuit according to the invention
• FIG. 5 is a block diagram of an electronic ballast in which the bridge circuit shown in FIG. 4 is used; and Fig. 6 shows a known VoUbruckensclien.
• the arrangement of the four field effect transistors S1 to S4 of the full bridge shown in FIG. 1 is identical to the known arrangement from FIG. 6. Again, a DC voltage U BUS is applied to the input of the bridge circuit, the output of the bridge circuit is formed by a shunt connected to ground. Resistor R. However, only the gas discharge lamp LA is now connected as a load; the elements of a resonance circuit are no longer present in the first exemplary embodiment. Switching between the two bridge diagonals takes place in turn by the two driver circuits T1 and T2, which control the four field effect transistors S1 to S4 in a suitable manner.
• the regulation of the lamp brightness is no longer carried out by switching the switches S1 to S4 on and off by the driver circuits T1 and T2, but by controlling the field effect transistors S2 and S4 arranged in the bridge diagonals as controllable constant current sources.
• these two field effect transistors S2, S4 are each operated by an operational amplifier OP1 or OP2 in their modulation range. They thus form a resistor which is connected in series with the lamp LA and in this way defines an operating point for the lamp LA.
• the controllable constant current sources are therefore connected by the two lower field effect transistors S2 and S4 of the two half bridges and the two operational amplifiers OP1 and OP2, each of which controls the corresponding field effect transistors S2 and S4.
• a feedback line 9j and 9 2 the current flowing through the respective field effect transistor S2 or S4 current to the operational amplifier OPL, OP2 is supplied as an actual value, the second input signal forms a corresponding one of the desired lamp brightness value I S0LL, for example, the two operational amplifiers OPL, OP2 by a dimming circuit or the like can be supplied.
• the two operational amplifiers OP1 and OP2 act as controllers which set the current flowing through the two field effect transistors S2 and S4 to a value corresponding to the setpoint I SHOULD .
• the two driver circuits T1 and T2 are supplied with the control commands required for switching between the two bridge diagonals in the usual manner by a control circuit (not shown).
• a control circuit not shown.
• there is a low-frequency change between the two diagonals of the bridge in order to reduce the mercury migration in the lamp LA which results from single-sided DC operation.
• the use of a current-limiting inductor can be dispensed with.
• the voltage drop across them should be relatively low. At the same time, however, it should have a certain minimum value in order to ensure that the two field effect transistors S2 and S4 are operated in their linear region in order thus to enable effective current regulation.
• the ballast also has a control circuit 1, to which the voltage drop across the field effect transistor S2 or S4 of the respectively active bridge diagonal is supplied as an actual value via the two input lines 10 x or 10 2 .
• This actual value is compared with a setpoint I FETSOU * which corresponds to the value that enables a particularly effective current control.
• the control circuit 1 generates a control signal which is used to control the DC voltage U BUS .
• Fig. 2 shows the block diagram of a ballast.
• the input of the ballast is formed by a rectifier circuit 11 connected to an AC voltage source, for example a full-bridge rectifier, which supplies a rectified AC voltage U 0 to a first switching regulator 3.
• This first switching regulator 3 is formed by a step-up converter, which generates a high intermediate circuit voltage U z , which is fed to a second switching regulator 4.
• This second switching regulator 4 is a step-down converter which reduces the high intermediate circuit voltage U z to the required lower value for the direct voltage U BUS .
• the reference numeral 2 designates the bridge circuit shown in FIG. 1.
• the control circuit 1 controls the buck converter 4, in such a way that it generates a DC voltage U BUS , which, as provided, is only slightly above the lamp voltage LA, so that the via the two transistors S2 or S4 falling voltage corresponds to the setpoint U FETsoll .
• a DC voltage U BUS which, as provided, is only slightly above the lamp voltage LA, so that the via the two transistors S2 or S4 falling voltage corresponds to the setpoint U FETsoll .
• FIG. 3 the smoothing circuit for generating the DC voltage U BUS is not used.
• two switching regulators connected in series are generated, but by a buck boost converter 5, in which the functions of the switching regulators 3 and 4 shown in FIG. 2 are combined in one circuit. This integration is possible because the requirements for the control speed of the smoothing circuit are relatively low and therefore there is no fear of harmonics occurring at the input of the ballast due to rapid changes in frequency and / or duty cycle.
• the regulation of the lamp current by the two controllable constant current sources according to the invention has, in addition to the suppression of flickering, also the consequence that when the lamp LA is switched on at low lamp brightness, no flash can occur, since the current due to the two controllable constant current sources from the beginning to the desired value is limited.
• the lamp LA is thus ignited at a current which has the lowest possible value for triggering the ignition process.
• the buck converter 4 or the buck boost converter is controlled in such a way that it provides a maximum output voltage which is sufficient for the ignition. Another option is to use an ignition coil.
• the electronic ballast With the electronic ballast according to the invention, it is possible to dim and ignite the gas discharge lamp to 1/1000 of its maximum brightness without any flickering or a switch-on flash occurring. It is also advantageous that the lamp wiring has no influence on the dimming operation. This is because switching is still carried out at a low frequency, but the high-frequency switching of switches is dispensed with and therefore there is no influence of the wiring impedances due to this "quasi-direct current".
• the low-frequency pole reversal frequency ie the change between the two bridge diagonals, should be avoided Thereby lie at least slightly above the frequency that is still perceived by the eye, that is at least above 100 Hz. A frequency between 700 Hz and 2000 Hz is particularly advantageously selected.
• FIG. 4 A second exemplary embodiment of the bridge circuit according to the invention is shown in FIG. 4. This differs on the one hand in that the gas discharge lamp LA is again part of a resonance circuit consisting of an inductor L and a capacitor C, which is connected as a load of the bridge circuit, and on the other hand in that the regulator 1 described in FIG. 1 to regulate the DC voltage U BUS is dispensed with.
• the DC bridge circuit 2 is supplied with a constant DC voltage U BUS , as shown schematically in FIG. 5.
• the electronic ballast shown in FIG. 5 now has the rectifier circuit, a step-up converter 3 and the bridge circuit 2.
• the two controllable constant current sources consisting of the operational amplifiers OP1 and OP2 and the associated field effect transistors S2 and S4 are provided in the bridge circuit shown in FIG. Due to the constant DC voltage U BUS in its level, there is now the danger that at high lamp currents, that is to say at high brightness, the power loss resulting from the two transistors S2 and S4 increases to an impermissible level.
• the function of the two controllable constant current sources is suppressed and the four transistors S1 to S4 are activated as in the known method shown in FIG. 6. That is, a relatively low frequency is used to switch between the two diagonals of the bridge, one of the two transistors being clocked at high frequency during the on-time of a diagonal of the bridge, so that the lamp is operated with a direct current with a high-frequency ripple current superimposed on it.
• control with a variable pulse duty factor is necessary; in this operating mode, the inductance L forms the current-limiting impedance in series with the lamp.
• the control circuit 6 for controlling the LampenheUtechnik is responsible again and transmitted via the lines 8j to 8 4, the corresponding control commands to the drive circuits Tl and T2, which, accordingly, the four transistors Sl control up S4.
• the line capacities and line inductances do not play despite the high switching frequency Role, because they can be neglected relative to the lamp current and therefore do not interfere with the control processes. At these high brightnesses, there is also no risk of flickering. At low brightness values, there is again the ideal ignition behavior due to the current control, with which the occurrence of light flashes is suppressed. Again, dimming up to 1/1000 of the maximum lamp brightness is possible.
• the concept according to the invention is thus characterized in that lamp operation is realized with which dimming over a very wide brightness range is made possible. In addition, there is the possibility of starting the lamp even at very low brightness values without flashes of light which are perceived as unpleasant.

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• Circuit Arrangements For Discharge Lamps (AREA)
• Inverter Devices (AREA)

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• 2000
  • 2000-10-16 DE DE10051139A patent/DE10051139A1/de not_active Ceased
• 2001
  • 2001-09-11 AT AT04013891T patent/ATE419735T1/de not_active IP Right Cessation
  • 2001-09-11 EP EP01974243A patent/EP1330945B1/fr not_active Expired - Lifetime
  • 2001-09-11 AU AU9380701A patent/AU9380701A/xx active Pending
  • 2001-09-11 AU AU2001293807A patent/AU2001293807B2/en not_active Ceased
  • 2001-09-11 ZA ZA200302354A patent/ZA200302354B/en unknown
  • 2001-09-11 DE DE50114634T patent/DE50114634D1/de not_active Expired - Lifetime
  • 2001-09-11 WO PCT/EP2001/010497 patent/WO2002034015A1/fr active IP Right Grant
  • 2001-09-11 AT AT01974243T patent/ATE291341T1/de not_active IP Right Cessation
  • 2001-09-11 EP EP04013891A patent/EP1465465B1/fr not_active Expired - Lifetime
  • 2001-09-11 BR BR0114678-5A patent/BR0114678A/pt not_active Application Discontinuation
  • 2001-09-11 DE DE50105645T patent/DE50105645D1/de not_active Expired - Lifetime
• 2003
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