Reduction of harmonics in gas discharge lamp ballasts

(42) Date of commencement of the patent: 15.11.1987 (45) Date of issue: 11. 7.1988 (30) Priority:

1. 6.1982 ZA 3819/82 claims. 7. 6.1982 ZA 3968/82 claims.

26.10.1982 ZA 7811/82 claims.

26.11.1982 ZA 8709/82 claims.

(56) Documents:

GB-0S2106339 G8-OS2071949 DE-AS1764624 DE-OS2706513 US-PS 3084283 US-PS 2971126 (73)

CONTROL LOGIC (PROPRIETARY) LIMITED

DURBAN (ZA).

(54) CIRCUIT FOR THE OPERATION OF GAS DISCHARGE LAMPS

OO

AT 386 103

WRwnasia

- 2 No. 386103

The invention relates to a circuit for the operation of gas discharge lamps with a rectifier, preferably a multi-way rectifier and a smoothing capacitor and two lying between the supply lines of the rectifier in series switching devices for high-frequency, change circuit of an output connected between the switching devices output, on which a Inductance, the gas discharge lamp is connected, which forms the load circuit.

Such circuits generally have a capacitive equalizing filter arranged between the rectified voltage and the circuit (ballast) itself. This trimming capacitor causes distortion of the current waveform by harmonics in periods during which the rectified voltage is higher than the voltage across the trimming capacitor, as well as during the charging time of the capacitor. This charging time or the passage angle is very small when using a large capacitor, and the entire required charge must be introduced into the capacitor in a short period of time. This results in a high current power from the rectified supply during the short conduction angle and causes current spikes in the rectified supply.

These current spikes increase the harmonic content of the power supply, and with multiple ballasts, this increased harmonic distortion gives poor network power factor. This situation is disapproved by the electricity supply authorities, which generally dictate the minimum allowable power factor and / or the maximum allowable harmonic distortion.

A known solution to this problem is to use an inductive and capacitive filter between the rectified voltage and the input of the ballast in order to suppress the current spikes. This requires the use of extremely large throttles, which are expensive and require a lot of space.

It is also known to apply a Speicherumformerprinzip, whereby a throttle at high frequency is controlled to allow charging of the balancing capacitor over a wide transmission angle. However, this system requires a memory converter control circuit to control the current discharge from the storage choke. Such an application of the storage transducer principle is described in ZA-PS No. 81/2504. This circuit is relatively complicated and expensive to manufacture.

From GB-PS No. 2,071,949 a circuit is known, which aims primarily to avoid excessive voltage peaks in the series resonant circuit during start-up, and secondly that the oscillating transistors switch safely, to which saturation transformers with current feedback are used. Although this measure is used successfully in a circuit of the subject type, but it is not part of the claimed measure and invention. Similar circuits of this type are also described in US Pat. Nos. 3,084,283 and 2,971,126, which may be referred to here. Specific modifications of this prior art basic principle are also set forth in GB-A-2,106,339. In this prior art circuit, the smoothing capacitor is not disconnected from the supply device. Here in this prior art circuit, the smoothing capacitor is charged to the top of the mains voltage and then discharges its energy into the load circuit, u.zw. during the periods between the peak voltage values ​​of the utility.

In another circuit (DE-OS 2706513), the power supply frequency for the gas discharge lamps is kept as close as possible to the resonant frequency of the load circuit in order to operate the operating circuit with high efficiency. Here, the resonant circuit builds up a preselected voltage at which the ballast is turned on, and after this start, the load change across a capacitor causes a shift of the resonant frequency and consequently a lowering of the resonant voltage. The circuit previously known from the DE-OS mentioned makes reference to the fact that the conventional circuit for the above functions does not provide effective control of an AC frequency for load resistance values ​​between non-fired, cold lamps and hot, burning lamps. Thus, if such a circuit is used to re-start a partially ionized discharge lamp, it may fail to include the resonant frequency of the appropriate circuit.

Nr.386103

The prior art circuit thus relates to a circuit which can obtain the resonant frequency of the load circuit under different load conditions.

DE-OS 1764624 shows a circuit which aims to achieve the best possible starting behavior for a gas discharge lamp, u.zw. by means of electronic switching elements 5 in contrast to conventional inductive capacitor ballasts. The achieved by electronic switching means start is achieved here by the use of a damped oscillator circuit to achieve the necessary high starting voltage. Following the start, the vibrations are damped and thus ensure that the lamp can be operated at low voltage once it has ignited. The invention described in this prior publication relates to the use of a damped oscillator for starting a gas discharge lamp, which is switched to a conventional circuit for continuous operation after successful ignition.

The object of the invention is therefore to propose a circuit whose harmonic content in the power supply is kept as low as possible or as far as possible avoided at all. This is achieved by the combination of the following features that the gas discharge lamp is connected via at least one flyback capacitor with at least one of the two feed lines and in the flyback capacitor and smoothing capacitor connecting line is a half-wave rectifier and also at least one control capacitor via at least one switching device periodically in series with the Load circuit is switchable.

This circuit for the operation of a gas discharge lamp includes a rectified input voltage equalizing capacitor, and switching devices for alternately switching an output between positive and negative input supply lines in alternating positive and negative periods, each time elapsing between these switching operations of the output during which the switching devices are turned off are. The load circuit has an inductive element which can be driven in series by this output in order to drive a gas discharge lamp and a switching controller associated with the switching devices in order to switch them considerably faster than the half-period frequency of the rectified voltage. Further, a return is provided, for the rectified input between the load circuit and a feed line and a control capacitor, which is charged during the turn-on of a Schaltvor30 direction in series with the load circuit by the discharge of the balancing capacitor and causes a decrease in voltage across the load circuit. The one-way component connected to the feed line of the return prevents the discharge of the balancing capacitor along the feed line into the return line. A connection is also provided for conducting the charge from the inductive element into the load circuit to charge the trim capacitor during said particular times. The one-way component is connected and the return arranged so that the voltage reduction across the load allows current to flow from the rectified input through the return and load circuits, the control capacitor being sized to supply sufficient current from the rectified one for a given load

Voltage flows to flow together with any other flowing through the load circuit

Streaming, except that resulting from the discharge of the balancing capacitor current covers at least all circuit losses and the expected load loss and thereby ensures that the voltage across the balancing capacitor remains at least as high as the peaks of the rectified supply voltage.

Another feature of the invention provides that a control capacitor is connected to the gas discharge lamp except the flyback capacitor, on the other hand, is located at the positive terminal of the smoothing capacitor. The flyback capacitor is designed so large relative to the control capacitor that a voltage across the flyback capacitor from the stored therein during the turn-on time of a switching device charge from the rectified voltage, can exceed voltage occurring across the load circuit during the turn-on of the other Schaltvorrich50 device and thereby leads to a discharge from the flyback capacitor through the load circuit and supplies those coming from the rectified voltage current flow.

- 4 No. 386103

The control capacitor is connected between the load circuit and the feed line to which the return leads, so that a sufficient current flow resulting from the rectified voltage can take place directly from the rectified voltage during the duration of said lowered voltage across the load circuit. In addition, the return may include a flyback capacitor of a size that is designed in relation to the control capacitor so that it allows such a sufficient, coming from the rectified voltage current flow.

Further, a return for the rectified input between the load circuit and two supply lines is provided in each case via flyback capacitors, a first such leads to the positive and a second to the negative feed line, which return includes a first, connected to a feed line control capacitor, the one to this Feedline leading return capacitor is designed so large relative to the control capacitor that a portion of that current flow can take place directly from the rectified voltage during the periods of reduced voltage across the load, the return capacitor leading to the other supply line being designed so large relative to the control capacitor that the voltage above it is stored therein during other times Charge can exceed the voltage across the load circuit and cause a discharge therefrom, so that another part of that current flow can take place, the two parts of this current flow supplying it in sufficient magnitude.

There is also a pre-circuit, in which a return for the rectified input between the load circuit and two feed lines is seen in each case via flyback capacitors, a first such leads to the positive and a second to the negative feed line, and a first control capacitor with the positive and a second is connected to the negative feed line, wherein in both feed lines is a disposable component, wherein the first flyback capacitor and the second control capacitor are designed to be large enough to allow the lowered voltage resulting from the charging of the second capacitor during the turn-on time of a first switching device, a portion of that current flow directly from the rectified voltage through the load circuit and the second Return capacitor to flow, and also make it possible during the turn-on time of a first switching device, the voltage across the first flyback capacitor as a result of the charge stored therein from the rectified voltage during the turn-on time of the second switching device exceeds that lowered voltage across the load circuit and allows discharge of the first flyback capacitor, thus part of that current flow takes place through the disposable component in the positive supply line into the load circuit.

The second flyback capacitor and the first control capacitor are designed so large that they allow during the turn-on of the second switching device that resulting from the charging of the first flyback capacitor reduced voltage, a portion of that current flow directly from the rectified voltage through the load circuit and the first Return capacitor to flow, and also make it possible that the voltage across the second flyback capacitor as a result of the charge stored therein from the rectified voltage during the turn-on time of the first switching device exceeds this lowered voltage across the load circuit and allows discharge of the second flyback capacitor so that a portion of that current flow through the one-way component in the negative Feed line into the load circuit, and wherein the sum of all parts of this current flow provides said sufficient current flow.

In this case, two further connections are provided for the control capacitors, with the first such connection being connected in parallel to the one-way component in the positive supply line and the second control capacitor in parallel to the one-way component in the negative line. With the second type of control capacitor terminal, the first control capacitor is connected to the positive supply line for the load circuit and the second control capacitor to the negative supply line for this.

Further, an input reactor is provided, which is to be connected in series with the load on the rectifier input side of the disposable components and is designed so large that they

No. 386103 reduces odd harmonics in the current waveform of the supply.

In addition, preferably, a high-frequency bypass capacitor is connected in parallel with the rectified output.

The rating of the capacitor sizes can be made so that a largely stable voltage across the capacitors results, or even so that the balancing capacitor voltage increases increasingly, in which case a clamping circuit must be provided so that the voltage does not exceed a predetermined maximum value.

It is also contemplated that the clamping circuit comprises a circuit breaker which is connected so that it shorts at least one of those disposable components in a supply line when driving, and a transmitter for driving the circuit breaker upon detection of a voltage above the predetermined maximum value. Preferably, the switching device is a pre-controlled by this encoder thyristor.

In cases where the voltage across the load circuit must operate a gas discharge lamp with a high operating voltage, it may happen that this voltage drops below the operating voltage of the lamp by the voltage drop, and it is provided that the load circuit includes a series resonant circuit and the terminals a capacitive element of which can take over the load of a parallel to this capacitive element to be operated gas discharge lamp.

Further features of the invention will become apparent from the following description of preferred, only exemplary embodiments of the invention with reference to the drawings; FIG. 1 shows a circuit diagram of an embodiment of the invention with current paths during a positive switching period; FIG. Figure 2 is a voltage and current diagram as a function of time in a switching device for the circuit according to Fig.l; FIG. 3 shows a circuit diagram with current paths in the circuit according to FIG. 1 between the switching periods · after a positive period; FIG.

FIG. 4 shows the circuit according to FIG. 1 with current paths during a negative switching period; FIG. FIG. 5 shows the circuit diagram according to FIG. 1 with current paths between the switching periods after a negative period; FIG. FIG. 6 shows a circuit diagram of the embodiment according to FIG. 1 with an inductive input filter; FIG. Fig. 7 is a graph of the voltage across the flyback capacitors of the circuit of Fig. 6; 8 is a circuit diagram of another embodiment of the invention with current paths during a positive switching period; FIG. 9 shows the circuit diagram according to FIG. 8 with current paths between the switching periods after a positive period; FIG. 10 shows a circuit diagram for a modified circuit according to Figures 8 and 9. 11 to 14 are circuit diagrams for further embodiments of the invention in different switching stages and FIG. 15 to 18 circuit diagrams according to a further embodiment of the invention in different switching states.

Referring to Fig. 1, a ballast circuit, generally designated -1-, is supplied with rectified voltage from the positive and negative leads -2, 3-, respectively, of a two-way bridge rectifier -4- to an AC input -5-.

The positive lead -2- from the anode to the cathode passes from the bridge through a diode -6- to a trim capacitor -7-, and the negative lead -3- from the cathode 40 to the anode runs from the bridge via a diode -8 - to the other side of the balancing capacitor -7-. Two serial switching devices -9 and 10 connected in parallel to the balancing capacitor -7- can be alternately switched on and off with a certain gap between two circuits. This switching frequency is preferably about 20 kHz for a 50 or 60 kHz power input -5-. Between the balancing devices, an output line 45 -11- is connected to the positive line through the device -9- and the negative line is connected to the device -10-.

The output line -11- drives a series resonant circuit with a Dossei -12- and a capacitor -13-, to which a discharge tube as load -14- is connected in parallel. This series resonant circuit and the lamp form the load circuit.

The series resonant circuit is connected to the balancing capacitor side of the diode -6 or 8- via the control capacitor -15- with the positive line or via the control capacitor -16- with the negative line and runs to the positive line on the bridge side of the diodes -6 and 8- through the reflux condenser -17- to the positive line and return condenser -18- to the negative line.

Nr.386103

Damping diodes -19 and 20- are cross-connected through switching devices -9 and 10, with diode -19- from anode to cathode from the negative side via device -10- to output line -11- and diode -20 - From the anode to the cathode of the output line -11- to the positive side on the device -9- verbun5 is.

Fig. 2 now shows a voltage and current diagram of a switching device of the circuit as a function of time. Since this circuit is inductive, the current lags behind the voltage by a time 21.

Initially, the current from the diode bridge -4- charges the capacitor -7- via the 10 diodes -6 and 8- and at the same time the capacitors -15, 16, 17 and 18-. Capacitor -7- is much larger than the rest and is charged to a voltage equal to the peak supply minus the voltage drop across diodes -6 and 8-.

At some time during charging of the capacitor -7-, the switching devices -9 and 10 become conducting at a much higher frequency than that of the supply. For switching the devices, not shown control circuits are provided. It is known to the person skilled in the art that a wide variety of circuits can be used for this function. The switching on and off of the device -9- results in a positive square waves wave 22 (Figure 2) and switching the device -10- a negative Rech teckwel len pulse 23 (Figure 2).

From FIG. 1, four current paths are still visible when the device -9- is switched on:

The path 24 travels from the positive side of the capacitor -7- via the switching device -9-, the load and the capacitor -16- back to the capacitor -7-; the path 25 runs from the positive side of the capacitor -17- via the switching device -9- and the load back to the capacitor -17-; the path 26 runs from the positive side of the capacitor -15- via the switching device -9- and the load back to the capacitor -15-; and path 27 runs from the positive side of the supply via diode -6 and across the load back to capacitor -18-.

The capacitors are dimensioned so large that:

C_? much bigger than C₁₇ and C_lg greater than C_J5 and C_lg ,

With the following symbols:

Voltage across capacitor -15-: V_glgVoltage across capacitor -16-: V_glgVoltage across capacitor -7-: V_g7 it is understood that:

V »V + V ^v C7 CI5 ^v C16

From the current path 24 it can be seen that the capacitor -16- is charged by discharge from the balancing capacitor -7- in series with the load circuit, and since the capacitor -7- is much larger, the voltage is V_g7 almost constant. This leads to the charging of the capacitor -16- and to an increase in the voltage V_glg , and V_cig decreases with the 40 increase of V _c j _G by the same amount. Thus, the capacitor -15- is discharged via the path 26 in the load circuit. With the correct dimensions of the capacitors -15 and

16- will then decrease to 0V during the on-time of the switching device -9- Clo and V_glg against V_g7 increase.

So that power line takes place, the rectified supply voltage must be greater than 45, the voltage across the load circuit plus V_gl8 or v_s > V_lg + V_gl8 his.

Nr.386103

It is also clear that V _cl5 at the same time represents the voltage across the load circuit, so that with the increase of V_C16 the load circuit voltage decreases and the rectified supply may be conductive during the period when the load circuit voltage drops below the instantaneous supply voltage.

At some time during the fall of V_cl5 becomes V_C17 greater than V_C18 and the required voltage drop across the diode -6-. This results in a current discharge from the capacitor -17-, which contributes via the current path 25 to the load.

Although V_C17 at times during the coverage period much lower than V_C15In this way, the capacitor 17 will still be able to discharge along the path 25 into the load circuit due to the lowering of the load circuit voltage.

With the following symbols:

Voltage across capacitor -17-: V_cl7Voltage across capacitor -18-; V_cl8Instantaneous supply voltage: v_s surrendered:

The capacitor -18- is therefore charged simultaneously from the supply, so that V_C18 by the same amount as the drop in C _cl7 increases.

In parallel with the diode -8- is shown a thyristor -37A- whose gate is from a

Encoder -28- is controlled, which samples the voltage across the Abgleichkondensatoi -7-. If V_C7 is too high, the thyristor turns on and short-circuiting the diode -8-, so that a further construction of V _c7 is prevented.

When the device -9- is switched off, the device -10- does not switch on immediately and a certain time elapses before this happens. Figure 2 shows this as the time between the shutdown of the device -9- and the transition of the trailing current waveform from the positive side to the negative side of the zero point of the time axis. If the switching of the devices is controlled by current feedback means, it can obviously be provided that this time is always determined by the above parameters, since that on the negative

Side current waveform will trigger the device -10-.

In Fig. 3, the circuit is the same as described with reference to Fig. 1, and the reference numerals refer to the same circuit components; however, as described below, the current paths are different. When switching off the device -9- and because of the phase shift -21- shown in Figure 2 leads the collapse of the throttle -12- associated magnetic field seen that the current path 29 from the positive side of the capacitor -7- through the Diode -19- and the load circuit in two paths through the capacitors -17 and 15- and back to the capacitor -7- splits. This turn-off time of both devices is shown in Figure 2 as the period from 30 to 31 and represents the charging current for the capacitor -7-. The area under the sinusoid in Figure 2 represents the charge, u.zw.

Over the period 30 to 31, the charging of the capacitor -7-, while the charge in the period 32 to 30, the on-time of the device -9-, discharge from the capacitor -7- and the supply is. If the supply contribution during the latter period (32 to 30) is so great that the charge of the capacitor -7- during the preceding period (30 to 31) is higher than the discharge of this capacitor (during the time period 32 to 30), then becomes V_c7 increase. It can be seen that the size of the control capacitor determines the speed at which the voltage across the load circuit drops during a turn-on time of the switching device and thus determines the length of time during which this supply contribution takes place.

Nr.386103

By choosing the circuit constants one can thus ensure that V_c7 is always higher than the supply peak voltage, so that the capacitor -7- is no longer charged directly from the supply after the initial charge and the utility contribution covers the circuit and load losses. You can achieve equilibrium so that V_C7 remains stable, or one can let it rise to a maximum value, where it is clamped off, for example, by the thyristor and encoder -27 and 28- to Fig.l.

Referring to Fig. 4, there is shown the same circuit as described with reference to Fig. 1, wherein the reference numerals designate the same circuit components. 4, however, the switching device -10- is now turned on, and four current paths can be seen: path 33 runs from the positive side of the capacitor -7- through the capacitor -15-, the load circuit, the

Switching device -10- and back to the capacitor -7-; Path 34 goes from the positive side of capacitor -18- through the load circuit, switching device -10- and back via diode -8- to capacitor -18-; the path 35 runs from the positive side of the

Capacitor -16- through the load circuit, the switching device -10- and back to the capacitor -16-; Finally, the path 36 runs from the positive side of the supply through the capacitor -17-, the load circuit, the switching device -10- and back to the supply via the diode -8-.

The control capacitor -15- is charged via path 33 in series with the load circuit by discharging the trim capacitor -7-. With the increase of the voltage across the capacitor -15- (V_C15 ) takes the voltage across the capacitor -16- (^vCi6 ^{to the}same amount. At a certain moment, V is_clg lower than the voltage of the capacitor -18- (V _cl8 ), and at this time the capacitor -18- discharges and contributes to the load current.

At any given time, therefore, the capacitor -17- charges by means of the supply current path 36, so that V_C1? by the same amount as the drop of V_cl8 increases. Further, in a similar manner as described with reference to FIG_clg now the voltage across the load circuit, and a supply current contribution along path 36, takes place as soon as the instantaneous supply voltage is higher than V_cl7 and the falling load circuit voltage is.

Fig.5 now shows the circuit of Fig.l in a state where the switching devices are immediately after switching off the device -10- off. In Fig. 2, this is indicated as the time 37. In this position, the collapse of the magnetic field associated with the choke causes the current path 38 from capacitor -7- to capacitors -18 and 16-, the load circuit and diode -20- to return to capacitor -7-. These paths occur during the period 37 to 39 in Fig.2. It will be understood that the portions of pulses 22 and 23 drawn between dotted lines 30 and 31 and 39 represent the conductive state during periods when both devices -9 and 10 are turned off.

It will also be understood that the alternating charge and discharge of the capacitors -17 and 18- as described promotes the supply of a supply current over a longer period of supply periods. It can be seen from the current paths as described above and illustrates that during charging of the control capacitors -15 and 16- by the discharge of the balancing capacitor -7- the charge stored in a flyback capacitor during a half-cycle, which during the next half cycle in the load circuit is discharged from the rectified supply.

Since after the original charging of the capacitor -7- this is only charged by the throttle during the limited turn-off time of both switching devices, the discharge of the flyback capacitor in the load circuit and the direct rectified supply current contribution through the load circuit together cover the circuit and load losses.

Nr.386103

Referring now to Fig. 6, there is shown the same circuit as described with reference to Fig. 1, wherein the numbers indicate the same circuit components. In this case, however, the bridge rectifier -4- is located farther from the position where it supplies the capacitors -17 and 18- and charges a parallel-connected capacitor -40-, which in turn is connected across a choke. operates the positive rail between the anode of the diode -6- and the positive side of the capacitor -17-. The negative rail -3- is connected to the capacitor -18- and the negative side of the bridge.

The voltage across the capacitors -17 and 18- from the positive to the negative rail is plotted versus time in the graph of FIG. The main frequency is designated by the number -42- and the modulated switching device frequency by the reference number -43-. In practice it has been found that the incorporation of choke -41 and capacitor -40- contributes to a further reduction of the harmonics. It is believed that this results from the action of these components on the current waveform, by converting the approximately rectangular wave at this point to an approximately sinusoidal waveform which, of course, contains less odd harmonics. This follows from the action of the choke, which makes the amount of charge flow passing through dependent on the more sinusoidal voltage shape.

8 and 9, a different, but similar embodiment is now apparent. A full wave rectifier bridge -44- draws an AC voltage from the mains -45- and provides rectified current to a positive line -46- and negative line -47-.

The positive lead passes from anode to cathode through a diode -48- to a trim capacitor -49-, and the negative lead -54- goes from cathode to anode through a diode -56- to the other side of the match capacitor -49-. Control capacitors -51- are each arranged in parallel with diodes -48 and 56-.

A switching device -52- is connected to the positive line -46- on its balancing capacitor side to connect the positive line to an output along the line -53-, and a similar switching device -54- is connected to the output line -53- negative line -47- connected to the balancing capacitor side of the diode -56-. The devices are alternately switched by a control circuit, not shown, which waits a certain time after switching off a device before it turns on the other device. The output line -53- supplies a series resonant circuit consisting of a choke -55- and a capacitor -70-, with a gas discharge lamp load -57- being in parallel with the capacitor. The series resonant circuit returns to positive line -46- via a flyback capacitor -58- on the bridge side of diode -48- and a flyback capacitor -59- on the bridge side of diode -56- to negative line -47-.

On the matching capacitor sides of diodes -48 and 56-, a damping diode -60- is connected from anode to cathode from negative line -47- in parallel with switching device -54- to output line -53-, and another such diode is connected. is disposed between the output line -53- and the positive line -46- in parallel with the switching device -52-. The capacitors -58 and 59- are proportioned in relation to the capacitors -51- so that the size of the capacitors -58 and 59- respectively exceeds that of the capacitors -51-, and the capacitor -49- is of course much larger than ever a capacitor -58-, capacitor -59- or one of the capacitors -51-.

The capacitors -58 and 59- serve as flyback capacitors, while the capacitors -51- form the control capacitors.

In operation, when the switching device -52- is switched on and the switching device -54- is switched off, the three current paths shown in FIG. 8 can be seen. The current path 61 runs from the positive side of the bridge -44- through the diode -48-, the device -52-, the load and back to the bridge via the capacitor -59-. The current path 62 passes from the positive side of the capacitor -49- through the switching device -52-, the load, the capacitor -59-, the control capacitor -51- in the negative rail and back to the capacitor -49-. The last current path 63 runs from the positive side of the capacitor through the diode -48-, the device -52-, the load and back to the capacitor -58-. The discharge current flow from the balancing capacitor -49- along the path 63 charges the flyback capacitor -59- and the negative-rail control capacitor -51- in series therewith, and since the two control capacitors are significantly smaller than either of the flyback capacitors, this capacitor will 51- up to a high voltage approaching the balancing capacitor voltage.

As a result, the voltage across the load circuit (V_LC), so that the rectified supply can be conducted along the path 61 when its voltage V_LC and the voltage across the capacitor -59- exceeds.

This lowered voltage V_LC across the load circuit also causes the capacitor -58- charged during the preceding half-cycle and the positive-rail capacitor -51- to discharge along the path 63.

While this embodiment is obviously different, its operation is subject to the same principles as described for the embodiment of Figs. 1-5.

The switching control circuit, not shown, switching devices -52 and 54, now turns off the device -52- and waits a certain time before turning on the device -54-. This position is shown in Fig. 9, where the circuit is the same as in Fig. 8 with the same reference numerals.

9, when both switching devices are off, the collapsing field of the inductor 55 leads to continued current flow along the path 64 that passes through the inductor to the return end of the series resonant circuit, through the capacitor 58, and into the diode 51. leads to charge the equalization capacitor -49-.

During a negative half-cycle with the device turned on, the charge on the flyback capacitor -59- is discharged by the same action as the charge in the flyback capacitor -58-.

It will be understood that the process just described is closely related to that described with reference to FIGS. In this embodiment, one must again receive a correct allocation of the discharge of the balancing capacitor -49- during the turn-on time of a switching device, so that during the turn-off of the two devices takes place charging of the capacitor -49- at least equal to the discharge.

It will also be appreciated that the current paths and operation of the circuit during the period when the switching device -52- is turned on and the subsequent period during which both switching devices are off are mirror images of the paths described with reference to Figs represent.

The circuit shown in Figure 10 has the same components with the same reference numerals as the circuit of Figures 8 and 9, except for the diode bridge -44- in Figures 8 and 9. Instead, a full-wave rectifier bridge -64- is provided in a split arrangement whose one pair of diodes -65- is connected in parallel with the capacitors -58 and 59- and whose other diode pair -66- is in parallel with the matching capacitor -49-. The AC input -67- is normally connected to the terminals of the two diodes in a pair. It has been shown in practice that the circuit operates with good effect, with the diode pairs -65 and 66- behave like a rectifier.

Fig. 11 to 14 show yet another embodiment. A full wave rectifier bridge -68- has a positive supply along line -69- and a negative supply along line -70- with the positive line -69- from anode to cathode through a diode -71- to one side of a trim capacitor -72 - leads. The negative line -70- is connected directly to the other side of the balancing capacitor.

A switching device -73- is connected between the diode -71 and the balancing capacitor -72- to the positive line -69- to switch an output line -74- to the positive line. Another switching device -75- is connected from the output line -74- down to the negative line -70- to switch the output line to the negative supply line. The switching device -73- has a damping diode -76- which is in parallel from anode to cathode from the output line

No.386103 ago connected to the positive supply. Similarly, an anode-to-cathode damper diode is connected from the negative line 70- to the output -74- in parallel with the switching device -75-. The output line -74- runs through a

Choke -78- and a gas discharge lamp load -79- back to positive supply line -69- through a flyback capacitor -80- on the anode side of diode -71-. A control capacitor -81- is connected from the positive line -69- on the cathode side of the diode -71- to the return end of the load circuit containing the choke -78 and the gas discharge lamp -79-.

Referring now to Fig. 11, there is shown the current switching circuit -75- circuit, and two current paths are apparent: the first path is the current path 82, which is a discharge of the matching capacitor -72- along the positive supply line through the control capacitor -81-, represents the load circuit, the switching device -75- and back to the balancing capacitor. A second path 83 passes from the positive side of the bridge rectifier through capacitor -80-, the load circuit, the switching device -75-, and back to the bridge.

The charging of the control capacitor -81- in series with the load circuit leads to a reduction in the load voltage, since they are both in series, so to speak, with the balancing capacitor -72-. Because the control capacitor is again significantly smaller than the trim capacitor and the flyback capacitor, the voltage across the load circuit drops rapidly, and as soon as the voltage across the load circuit is less than the rectified voltage, the current path 83 comes into effect, and the rectified Voltage then contributes directly to the load. The ratio of the relative contributions of the discharge from the balancing capacitor and the current flow from the bridge rectifier is determined by the relative size of the control capacitor -81- as described below.

Referring to FIG. 12, the circuit having both switching devices -73 and 75- is shown turned off according to the switching path of FIG. Again, two current paths are recognizable, a first path 84 from the inductor, as a result of the collapsing field around it, through the overshoot diode -76- into the trim capacitor and through the negative line -70-, through the bridge -68-, the flyback capacitor -80- and back to

Choke -78-. The current path 84 thus serves to charge the balancing capacitor -72-.

FIG. 13 shows a circuit with switched-on switching device -73- which follows the switching state described with reference to FIG. The one shown current path 86 follows from the discharge of the flyback capacitor -80- through the diode -71-, the Schaltvorrich35 device -73-, the load circuit and back to the capacitor -80-, and the second current path 87 shown results from the discharge of the Steurerkondensators -81- in the positive line through the switching device -73-, the load circuit and back to the control capacitor.

In Fig. 14, the circuit with both switching devices -73 and 75- is now shown off, which follows the switching state described in FIG. Two current paths are shown 40, namely the path 88 from the throttle -78- as a result of the collapsing field around it into the flyback capacitor -80- to the positive line, through the diode -71- and into the match capacitor -72- and from this passes through the snubber diode -77- back to the choke. The second current path 89 starts from the choke -78- branches off through the control capacitor -81- and reunites with the current path 88 for the rest of it. It is understood that again during the limited turn-off time of the two switching devices, the collapsing fields the ballast the charging of the

Adjustment capacitor -72- cause.

In general, the charging of the control capacitor -81- (Figure 11) causes a lowering of the voltage across the load and allows for a direct contribution from the rectified supply. If the pension contribution via path 83 (Fig. 11) in proportion to the contribution of the balancing capacitor discharge, it is possible to ensure that the circuit and load losses are covered, thereby allowing a sufficient supply contribution to the storage of energy in the choke, so as to eliminate any losses from the reactor

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Balancing capacitor -72- during its discharge by charging the balancing capacitor with supply energy in the choke during certain periods of time.

In this way, the voltage across the capacitor -72- to a suitable

Maximum value, which is above the peak voltage of the rectified supply.

It will be appreciated that one can replace the flyback capacitor -80- with a short circuit without significantly affecting the principle of the mechanism described above with reference to FIGS. 11-14. It is also understood that in the embodiment of FIG. 11 to 14, a negative rail version is possible with anode-to-cathode diode 71 disposed in the negative rail between the balance capacitor and rectifier, and capacitors -80 and 81-, as before, lead to the negative rail on either side of the diode , The current paths are exactly analogous to those described with reference to FIGS. 11 to 14. Further, if the version of this negative rail embodiment with the positive rail version of FIG. 11 to 14 combined, we obtain the embodiment of Fig.l.

In addition, it can be seen that when replacing the flyback capacitor -80- in this embodiment by a short circuit, the embodiment thus obtained a one-sided version of the embodiment of FIG. 8 and 9, taking away both the control capacitor from the negative rail and the flyback capacitor -59- and with replacement of the capacitor -58- is equivalent by a short circuit.

Yet another embodiment of the invention will be described with reference to Figs. In the circuit diagram in these drawings, the same reference numerals refer to the same components as described with reference to FIGS. 11 to 14, except that the control capacitor -81- as shown in FIG. 11 to 14 taken away and in Fig. 15 to 18 by a control capacitor -90- which is connected between the return of the load circuit and the negative rail.

Referring to Fig. 15, the device -75- is now on, and there is a single current path 91 leading from the positive end of the rectified supply through the flyback capacitor, the load circuit, the device -75-, and back to the rectifier. During this time, the flyback capacitor -80- is charged by the rectified supply.

In Fig. 16, after the switching state of the circuit of Fig. 15 both devices -73 and 75- are turned off, and the collapsing field around the choke -78- leads to a continued flow of current along the path 92 from the choke 78 through the Damping diode -76- to charge balancing capacitor -72- and back along negative rail through control capacitor -90- to choke -78-.

In Fig. 17, the switching device -73- on the switching state of FIG. 16 is turned on. Two electricity routes are recognizable. The first is a discharge path 93 from the balancing capacitor -72- through the switching device -73- and the load circuit until the charging of the control capacitor -90- and from this along the negative rail back to the balancing capacitor. During this time, the charging of the control capacitor -90- in series with the load circuit causes a drop in the load circuit voltage and as soon as it drops to a voltage lower than that across the flyback capacitor -80- plus the required diode drop across the diode -71- , the flyback capacitor will discharge back to itself along second path 94 through diode -71-, switching device -73- and the load circuit. The flyback capacitor -80- and the control capacitor -90- are designed so large that these current paths are possible.

In the circuit of FIG. 18, after the switching state of the circuit of FIG. 17, the devices -73 and 75- are both turned off. Throttle 78 allows continued flow of current along path 95 as a result of the collapsing field around it, and current flows from choke 78 through lamp -79-, flyback capacitor -80-, and diode -71- for charging of the balancing capacitor -72- as well as the paths from this through the negative rail, the overshoot diode -77- and back to the choke -78-.

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Thus, during the turn-off times of the two switching devices, the balancing capacitor is charged by the charge resulting from the collapsing field of the choke.

In this embodiment, the indirect contribution of the rectified supply 5 to the load circuit by the discharge of the flyback capacitor -80- is combined with the direct current path 91 of the rectified supply by the load to provide the sufficient current flow to cover the circuit and load losses and in To supply the throttle stored energy so that the voltage of the balancing capacitor is maintained at the required level.

The embodiments according to FIGS. 11 to 14 and 15 to 18 are suitable for the operation of

Low-voltage gas discharge lamps, but one must ensure that the voltage reduction across the load circuit does not drop the voltage across the lamp below its minimum operating voltage. If higher lamp voltages are required, a series resonant load circuit may be provided with the lamp over one of its reactive elements.

It is considered that the invention provides a useful circuit and method for

Reduction of clutter in ballasts for gas discharge lamps provides.