GB1575833A

GB1575833A - Discharge lamp operating circuit

Info

Publication number: GB1575833A
Application number: GB3612377A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1976-09-02
Filing date: 1977-08-30
Publication date: 1980-10-01
Also published as: AU507123B2; DE2738065A1; MX147056A; JPS6366040B2; ES461893A1; FR2363960A1; FR2363960B1; AU2850177A; NL7709673A; JPS5359273A

Description

(54) DISCHARGE LAMP OPERATING CIRCUIT (71) We, GENERAL ELECTRIC COMPANY, a corporation organized and existing under the laws of the laws of the State of New York, United States of America, of 1 River Road, Schenectady 12305, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to discharge lamp operating circuits.

The operating circuit of the invention may be used for applying DC pulses of predetermined duty cycle and repetition rate to a gaseous discharge lamp for improving the color and other properties thereof. A method and apparatus for pulsed operation of high pressure sodium vapor lamps for improving the color of such lamps are disclosed in our U.K. Patent application No. 1220/77 (Serial No. 1575831).

As disclosed in this application, the high pressure vapor lamp typically has an elongated arc tube containing a filling of xenon at a pressure of about 30 torr as a starting gas and a charge of 25 milligrams of amalgam of 25 weight percent sodium and 75 weight percent mercury.

The present invention seeks to provide an improved circuit for DC pulsed operation of such lamps in accordance with the method and principles disclosed in the aforesaid copending patent application. As therein disclosed, pulses may be applied to the lamp having repetition rates from 500 to about 2,000 Hertz and duty cycles from 10 /n to 30V0. By such operation, the color temperature of the lamp is readily increased and substantial improvement in color is achieved without significant loss in efficacy or reduction in lamp life.

The operating circuit of the invention may also be used for operating discharge lamps containing mixed metal vapors such as the above described lamp or other lamps in a manner to avoid color separation therein, in accordance with the method and principles disclosed in our US patent No.

4,128,789.

The invention provides a circuit for operating a gaseous discharge lamp, comprising in combination, a direct current power source, controlled switching means connected to said power source, unidirectional conducting means connected to said power source, means for connecting the gaseous discharge lamp to said power source, inductive means connected to said controlled switching means, said unidirectional conducting means, said lamp connecting means and said power source and control means being coupled to said controlled switching means for repetitively operating said controlled switching means at predetermined intervals, so that dc pulses may be applied to said gaseous discharge lamp for operation thereof and whereby energy stored in the magnetic field associated with said inductive means when power is being delivered to said discharge lamp by said power source may be conserved in said circuit when power is not being delivered to said discharge lamp by said power source.

The controlled switching means may include first and second switch means where said first switching means is in a first circuit branch across said power source, said unidirectional conducting means is in a second circuit branch across said power source, said inductive means being a transformer having a primary winding in said first branch in series with said first controlled switch means and a secondary winding in said branch in series with said unidirectional conducting means, said means for connecting a gaseous discharge lamp to said power source being in series with at least one of said branches and where said second controlled switch means is coupled to said secondary winding for substantially stopping current flow to said unidirectional conducting means and for storing magnetic energy in said transformer while said second controlled switch means is on and said control means being coupled to both said first and second controlled switch means for repetitively operating same at said predetermined intervals, whereby DC pulses may be applied to the gaseous discharge lamp for operation thereof.

The arrangement is such that when the first controlled switch means is opened, the described circuit operates to store a portion of the transformer energy in the power supply, and when the second controlled switch means is closed, the remaining transformer energy is maintained as a circulating current in the secondary winding.

Alternatively, the controlled switching means may include a first and second controlled switch means, said first controlled switch means and said inductive means connected in series across said power source, said means for connecting said lamp serially connecting said gaseous discharge lamp to said first controlled switch means and said inductive means, said unidirectional conducting means being connected across said series connected inductive means and said lamp connecting means, said second controlled switch means being coupled to said inductive means for stopping current flow to the gaseous discharge lamp and for storing magnetic energy in said inductance means while said second controlled switch means is on, and where said control means is coupled to said first and second controlled switch means for repetitively operating the same at said predetermined intervals, whereby DC pulses may be applied to the gaseous discharge lamp for operation thereof.

The inductive means may be an induction coil connected in series between the first controlled switch means and the lamp, with the second controlled switch means being connected across the induction coil. In another variation, the inductive means comprises a transformer having a primary winding as disclosed in our aforesaid U.S.

patent No. 4,128,789.

In a further embodiment, a gaseous discharge lamp may be connected in series with the controlled switch means across the power source, the unidirectional conducting means being connected across the power source, the inductive means may comprise a transformer having a primary winding connected in series with the controlled switch means and the lamp and a secondary winding connected in series with the unidirectional conducting means, said control means being coupled to the controlled switch means for repetitively operating the same at predetermined intervals, whereby DC pulses are applied to the gaseous discharge lamp for operation thereof.

In this form, the arrangement is such that when the switch means is opened, the transformer magnetic field begins to collapse, releasing stored energy, and the secondary winding and the unidirectional conducting means, e.g., a diode, operate to conserve this energy while also providing proper lamp pulse shape by allowing a reverse current back to the power supply.

The invention will be better understood from the following description of preferred embodiments, taken in conjunction with the accompanying drawings, in which: Figure 1 is a circuit diagram of a lamp operating circuit showing an embodiment of the invention; Figure la and lb show modifications of the Figure 1 circuit; Figure 2 shows a number of current wayeforms relating to the operation of the Figure 1 circuit; Figure 3 is a circuit diagram of the control circuit shown in Figures 1, la and Ib; and Figure 4 shows another modification of the Figure 1 circuit.

Figure 5 is a circuit diagram of a lamp operating circuit showing another embodiment of the invention Figure 6 shows a number of current waveforms relating to the operation of the Figure 5 circuit; Figure 7 is a circuit diagram of a modification of the Figure 5 operating circuit; and Figure 8 is a circuit diagram of the control circuit shown in Figures 5 and 7.

Figure 9 is a circuit diagram of a lamp operating circuit showing a further embodiment of the invention; Figure 9a and 9b shows modifications of the Figure 1 circuit; Figure 10 shows current waveforms relating to the operation of the Figure 9 circuit; and Figure 11 is a circuit diagram of the control circuit shown in Figure 9.

Referring now to the drawings and the invention in its first form, particularly to Figure 1, there is shown a circuit diagram illustrating an embodiment of the DC pulsing circuit of the invention for operating a gaseous discharge lamp 1, which is typically a high pressure sodium vapor lamp as described above. The circuit includes a DC supply source 2, such as a battery, to which is connected a pulsing circuit comprising two parallel branches connected across the supply source. One branch includes lamp 1 connected in series with primary winding LI of transformer 3 and transistor 5, and the other branch comprises diode 7 connected in series with transformer secondary winding L2. As indicated in the drawing, the primary winding and the secondary winding are arranged or connected so as to be out of phase with one another.Connected across secondary winding L2 as shown is silicon controlled rectifier (SCR) switch 6. Transistor switch 5 and SCR switch 6 are operated repetitively and sequentially, as more fully explained below, by timing (control) circuit 9 connected to the base of transistor 5 and the gate electrode of SCR 6. Control circuit 9 is shown in detail in Figure 3.

In the operation of the described circuit, and with reference to the waveform diagrams of Figure 2, when transistor switch 5 closes at time to, a current I1 begins to flow through lamp 1 and transformer primary L1.

This current increases with a time constant LIR where L is the inductance of primary winding Ll and R is the effective resistance of lamp 1. At time t1, switch 5 opens, thereby interrupting current flow through the lamp and winding Ll. At this time, there is energy stored in the magnetic field produced by the transformer current, the amount of energy being 1/2 LIp2, where Ip is the peak current flowing when switch 5 opens. This energy should either be stored in the circuit or dissipated in lamp 1, since to dissipate it elsewhere would decrease the efficiency of the lamp operating circuit. In accordance with the present invention, this energy is stored in two ways, as described below.When switch 5 opens at time t1 the magnetic field in transformer 3 begins to collapse, generating a voltage across both the primary and secondary windings. This voltage is of such polarity that when the voltage exceeds the supply voltage, a current I2 will flow into the power source.

Current I2 is initiated at some high value Ip' (see Figure 2), such that NsIp'=Nolp, wheie Ns and Np denote the number of turns on the secondary and primary windings, respectively. Current I2 decreases at a rate V/L', where V is the power supply voltage and L' is the inductance of secondary winding L2. Current I2 continues to flow until it reaches a value of about Ic, at time t2.

Then SCR switch 6 is triggered on by control circuit 9 and current I2 ceases, while current I3 is initiated and circulates through the loop containing secondary winding L2 and SCR switch 6 as shown in Figure 1. This current decays with a time constant L'/R' where R' is the resistance of SCR 6 and secondary winding L2. Since R' is quite small, this time constant is quite long, and current I3 does not decay appreciably.

Current I3 continues to flow until transistor switch 5 closes again, which results in commutation (turn-off) of SCR 6 and begins a new cycle.

A better understanding of the operation of the circuit will be obtained by a consideration of the energy flow and storage during various times of the described cycle.

At the instant switch 5 closes (at time t,), there is a current I, of instantaneous value 1o flowing in induction coil LI. This represents an amount of energy stored in the inductor of E,=1/2 LIo2. Just prior to the instant switch 5 opens at time t1, a current I, of value Ip is flowing through inductor Ll representing a stored energy of E2=l/2 LIp2.

Thus, the stored energy in the inductor has increased by BE=1/2 L (Ip2Io2) during this part of the cycle. In order to begin the next cycle with a current value of 1o, this energy, i.e., aE, must be removed from transformer 3 during the remainder of this cycle. This is accomplished in the following manner. When switch 5 opens and current I2 begins to flow, the energy stored in transformer 3 is E2. As the current through L2 and diode 7 decays to Io, the energy AE is returned to the power supply.

It is only after this energy is returned to the power supply that SCR 6 is turned on (time t2). If the SCR were turned on at time t, instead of t2, or if a diode were used in place of the SCR, then this energy AE would be dissipated in the SCR (or diode) and inductor L2. This would represent a power loss approximately equal to the lamp power, and would accordingly be undesirable.

However, most of this increment of stored energy is returned to the power supply, thus providing a highly efficient lamp ballast system which results in a high level of lamp system efficacy (lumens per watt). While SCR 6 is on, very little energy is dissipated, since the current is decaying only slightly, as previously noted. Thus, there is a base amount of stored energy E, in transformer 3 to which an increment AE is added in the time period to-ti and then subtracted in the time period t1-t2 in each cycle. As a result, a waveform as depicted in Figure 2 representing the lamp current is produced, characterized by a fast rise and fall.It has been found that such a waveform is particularly desirable in order to provide a substantial increase in color temperature of the gaseous discharge lamp in accordance with the principles disclosed in our aforementioned patent application No.

1220/77, (Serial No, 1,575,831).

As will be understood, the desired pulse repetition rate and duty cycle to obtain improved color properties of the lamp as disclosed in our aforementioned patent application No. 1220/77, (Serial No.

1,575,831) and U.S. patent 4,128,789 are with respect to the lamp current pulses, and control circuit 9 should accordingly be suitably adjusted to operate transistor switch 5 in such a manner as to provide the desired lamp current pulse repetition rate and duty cycle.

Figure 3 is a circuit diagram of control circuit 9 shown in Figures 1, la and lb, wherein the control circuit has four output terminals A, B, C, D, with terminals A and B connected to transistor 5 respectively at the base and emitter thereof, and terminals C and D connected to SCR switch 6 respectively at the gate and cathode thereof.

The function of control circuit 9 is to produce a base drive current in transistor 5 for closing that switch and to remove the base drive current to open the switch, the base drive being produced between terminals A and B. In addition, the control circuit produces a pulse of current at a sufficient voltage to trigger SCR 6 into conductive state, this pulse being produced between terminals C and D. For a pulse repetition rate of 1 kHz, a typical timing for operation of transistor 5 and SCR 6 (see Figure 2) when to=0 would be t,=100 microseconds and t2=200 microseconds.

The control circuit shown in Figure 3 comprises two timing networks each consisting of a 555 type integrated circuit and associated circuitry. The integrated circuits, shown as IC, and IC2, may be obtained commercially as type NE555 from Signetics Corporation.

The pins indicated for the illustrated IC circuits have the following functions: pin 1 is the power supply common (negative) voltage, pin 2 is the trigger input, pin 3 is the output voltage, pin 4 is the reset input, pin 6 is the threshold input, pin 7 is the discharge output, and pin 8 is the positive power supply input. The IC consists of a bistable circuit whose output voltage is either high (near positive power supply voltage) or low (near common or negative power supply voltage). The circuit is triggered into the high state when the voltage at trigger pin 2 goes below 1/3 V, where V is the power supply voltage. The circuit is triggered into the low state when the voltage at the threshold pin 6 goes above 2/3 V. The discharge pin 7 exhibits a short circuit to power supply common (pin 1) when the circuit is in the low state.

The timing network associated with IC, forms an astable multivibrator, whose output voltage has a waveform substantially like the base drive current waveform for switch 5 as shown in Figure 2. It will be noted that pins 2 and 6 are both connected to timing capacitor C,. Thus, when the voltage on C, goes higher than 2/3 V, threshold input pin 6 will cause the output voltage (pin 3) to go low and the discharge output (pin 7) shorts to pin 1. When the voltage on C, goes below 1/3 V, the trigger input (pin 2) will cause the output voltage to go high, and the short between the discharge output and pin 1 is removed, i.e;, the discharge output is turned off. In the operation of this circuit, assuming that the voltage on capacitor C, has dropped to 1/3 V, the output voltage at pin 3 is then high, and the discharge output (pin 7) is turned off.Then C, will charge through variable resistor R, and diode D, with a time constant R,C,. When the voltage on C, reaches 2/3 V, the output voltage will go low, and pin 7 is shorted to pin 1, resulting in discharge of capacitor C, through variable resistor R2 and pins 7 and 1 with a time constant R2C,. When the voltage on C reaches 1/3 V, the cycle begins again.

The timing network associated with IC2 forms a monostable multivibrator. When the output voltage of IC, (pin 3) goes low, a negative pulse is applied through capacitor C2 to the trigger input (pin 2) of IC2. This causes the output of IC2 to go high and pin 7 to turn off. Then capacitor C2 begins charging from zero volts through resistor R3 with a time constant R2C2. When the voltage on C2 reaches 2/3 V, the output voltage goes low, and C3 discharges through pins 7 and 1. The output then remains low until another trigger pulse is received from IC,. The output pulse is then differentiated by capacitor C4 and the negative transition of this output pulse is amplified and inverted by transistor Q2. This pulse is applied to the gate of SCR 6, as shown in Figure 3, to turn on the SCR.

The timing operation in terms of the waveforms shown in Figure 2 is such that at time to, IC, goes high, turning on transistor switch 5. At time t,. IC, goes low, turning off switch 5 and triggering IC2. At time t2, IC2 turns off (goes low), causing SCR switch 6 to be triggered on. A broad pulse is produced by IC, between time to and time t1, such as shown characterizing the switch drive current in Figure 2, and a narrow pulse (not shown) is produced by the action of IC2 at time t2 to gate the SCR on. After some time delay, IC1 again goes high, thus beginning a new cycle.

In the present described circuit, the provision of controlled switch 6 connected across transformer secondary winding L2 provides for energy to be stored in the transformer for a relatively long time and results in faster rise times of the lamp current pulses, as compared to the circuit described in conjunction with another embodiment to be described hereafter as the third form of the invention.

Further in the present circuit, the increment of energy AE is returned to the power supply as hereinabove described, in contrast to the circuit of the yet another embodiment to be described hereafter as the second form of the invention where this energy is dissipated in the lamp.

Figure la shows a modification of the Figure 1 circuit wherein the lamp is located in the main supply line in series between the DC supply and the junction of the described parallel branches containing the transformer primary and secondary windings, respectively. In such arrangement, the pulses applied to the lamp during operation will have a waveform characterized by a composite of the waveforms for I, and I2 as shown in Figure 2.

Figure lb shows another modification of the circuit wherein the lamp is located in the secondary winding branch in series with L2 and diode 7. In this case, the waveform of the lamp current will be like that shown for I2 in Figure 2.

Figure 4 shows another modification of the circuit of the present invention wherein transformer 3a includes tertiary or auxiliary winding L3, which may be tightly or loosely coupled to the primary and secondary windings, and SCR switch 6 is connected across tertiary winding L3. The operation of this circuit is essentially the same as the above-described circuits, except that in this case currents I2 and I3 would not go through the same winding. This provides the advantage that SCR 6 and diode 7 may be selected as to current and voltage rating with reference only to the respective transformer winding to which they are connected. In addition, the SCR is isolated from the power supply, with the attendant advantages thereof.

The DC supply source 2 is shown and described as a battery, but it will be understood that other forms of DC supply may be employed, as for example a circuit including a rectifier connected to an AC source and a filter capacitor connected to the output of the rectifier.

While an independent DC voltage supply V, which may typically be about 15 volts, is shown connected to the control circuit in Figure 3, it will be understood that, if desired, the control circuit may be connected to the DC supply of the power circuit, with the provision of suitable means for reducing the voltage.

Although particular types of controlled switches 5 and 6 are shown and described, it will be understood that other types of controlled switches may be employed for either or both of these components, as appropriate.

Referring now to the second form of the invention and particularly to Figure 5, there is shown a circuit diagram illustrating an embodiment of the DC pulsing circuit of the invention for operating a gaseous discharge lamp 1, which is typically a high pressure sodium vapor lamp such as described above.

The circuit comprises terminals 2 of a source of alternating current, and induction coil Ll connected at one side to one of the source terminals and at the other side to an input terminal of full wave bridge rectifier 3, which comprises diodes Dl, D2, D3 and D4 arranged in conventional manner as shown, the other input terminal of rectifier 3 being connected to the other source terminal 2.

Filter capacitor 4 connected across the DC supply circuit provides a filtered DC voltage supply for the pulsing circuit described hereinafter and increases the average voltage supplied thereto. Induction coil Ll serves to limit current to the lamp at the starting and warm-up stage.

The pulsing circuit illustrated in Figure 5 comprises transistor switch 5, induction coil L2 and lamp 1 connected in series across filter capacitor 4, silicon controlled rectifier switch (SCR) 7 connected across induction coil L2, and coasting diode 8 connected across the serially connected induction coil L2 and lamp 1. Induction coil L2, lamp 1 and diode 8 thus form a discharge loop, with transistor switch 5 being connected between the DC supply source and this discharge loop. SCR switch 7 and transistor switch 5 are operated repetitively and sequentially by timing (control) circuit 9 connected to the gate electrode of SCR 7 and the base of transistor 5. Control circuit 9 is shown in detail in Figure 8.

In the operation of the described circuit, and assuming that lamp 1 is in steady state operation with SCR switch 7 turned on and switch 5 turned off, a current 13 is flowing in the loop comprising SCR 7 and induction coil L2. With reference to Figure 6, the instantaneous value of I3 is designated as Io At this time only a small voltage appears across inductor L2. When transistor switch 5 closes at time to by operation of control circuit 9, a substantially higher voltage appears across inductor L2 and results in commutation (turn-off) of SCR 7 and flow of current I, through the series circuit of switch 5, inductor L2, and lamp 1 back to the power source. Current I, then increases with a time constant L/R, where L is the inductance of L2 and R is the effective resistance of lamp 1.This current increases until switch 5 opens at time t, at-which time it has a peak value Ip. At the same time, the voltage across inductor L2 reverses polarity, and current I2 begins to flow through the loop comprising inductor L2, lamp 1, and coasting diode 8. As seen in Figure 2 in the I2 waveform, this current starts at it and decays with the time constant L/R. Current I2 continues to flow until it reaches a value of approximately lo at time t2. Then SCR 7 is triggered on by control circuit 9 and current I2 ceases, while current I3 is initiated. This current decays with a time constant L/R' where R' is the resistance of SCR 7 and induction coil L2. Since R' is quite small, this time constant is quite long, and current I3 does not decay appreciably.

Current I3 continues to flow until transistor switch 5 closes again, which begins a new cycle. As will be seen, with the three currents I" I2 and 13, there is continuous current flow through inductor L2 during an operating cycle.

At the instant switch 5 closes (at time t,), there is a current I, of value 1o flowing in induction coil L2. This represents an amount of energy stored in the inductor of E,=1/2 LIo2. When switch 5 opens at time t" a current I, of value I is flowing through inductor L2 representing a stored energy of E2=l/2 LIp2. Thus, the stored energy in the inductor has increased by hE=1/2 L (Ip2Io2) during this part of the cycle. In order to begin the next cycle with a current value of Io, this energy, i.e., aE, must be dissipated during the remainder of this cycle. This is accomplished in the following manner.

When switch 5 opens and current I2 begins to flow, the energy stored in L2 is E2. As the current through L2, lamp I and diode 8 decays to lo, the energy is dissipated in the lamp. In accordance with the invention, it is only after this energy is dissipated in the lamp that SCR 7 is turned on (time t2). If the SCR were turned on at time t, instead of t2 or if a diode were used in place of the SCR, then this energy AE would be dissipated in the SCR (or diode) and inductor L2. This would represent a power loss approximately equal to the lamp power, and would accordingly be undesirable. However, most of this increment of stored energy is dissipated in the lamp, thus providing a highly efficient lamp ballast system which results in a high level of lamp system efficacy (lumens per watt).While SCR 7 is on, very little energy is dissipated, since the current is decaying only slightly, as previously noted. Thus, there is a constant amount of stored energy E, in inductor L2 to which an increment AE is added in the time period to-t, and then subtracted in the time period t1-t2 in each cycle. As a result, a waveform as depicted in Figure 6 representing the lamp current is produced, characterized by a fast rise and fall. It has been found that such a waveform is particularly desirable in order to provide a substantial increase in color temperature of the gaseous discharge lamp in accordance with the principles disclosed in out aforementioned patent application No.

1220/77, (Serial No. 1,575,831). The means provided in accordance with the present invention for efficiently storing energy in the inductor as described above makes possible lamp current rise and fall times of the order of microseconds, corresponding to the switching speeds of transistor 5 and SCR 7.

As will be understood, the desired pulse repetition rate and duty cycle to obtain improved color properties of the lamp as disclosed in the aforementioned U.K. patent application and U.S. patent are with respect to the lamp current pulses, and control circuit 9 should accordingly be suitably adjusted to operate transistor switch 5 in such a manner as to provide the desired lamp current pulse repetition rate and duty cycle.

Figure 8 is a circuit diagram of control circuit 9 shown in Figures 5 and 7, wherein the control circuit has four output terminals A, B, C, D, with terminals A and B connected to transistor 5 respectively at the base and emitter thereof, and terminals C and D connected to SCR switch 7 respectively at the gate and cathode thereof.

The function of control circuit 9 is to produce a base drive current in transistor 5 for closing that switch and to remove the base drive current to open the switch, the base drive being produced between terminals A and B. In addition, the control circuit produces a pulse of current at a sufficient voltage to trigger SCR 7 into conductive state, this pulse being produced between terminals C and D. For a pulse repetition rate of I kHz, a typical timing for operation of transistor 5 and SCR 7 (see Figure 2) when to=0 would be t,=100 microseconds and t2=200 microseconds.

The control circuit shown in Figure 8 comprises two timing networks each consisting of a 555 type integrated circuit and associated circuitry. The integrated circuits, shown as IC, and IC2, may be obtained commercially as type NE555 from Signetics Corporation.

The pins indicated for the illustrated IC circuits have the following functions: pin I is the power supply common (negative) voltage, pin 2 is the trigger input, pin 3 is the output voltage, pin 4 is the reset input, pin 6 is the threshold input, pin 7 is the discharge output, and pin 8 is the positive power supply input. The IC consists of a bistable circuit whose output voltage is either high (near positive power supply voltage) or low (near common or negative power supply voltage). The circuit is triggered into the high state when the voltage at trigger pin 2 goes below 1/3 V, where V is the power supply voltage. The circuit is triggered into the low state when the voltage at the threshold pin 6 goes above 2/3 V. The discharge pin 7 exhibits a short circuit to power supply common (pin 1) when the.

circuit is in the low state.

The timing network associated with IC, forms an astable multivibrator, whose output voltage has a waveform substantially like the base drive current waveform for switch 5 as shown in Figure 8. It will be noted that pins 2 and 6 are both connected to timing capacitor C,. Thus, when the voltage on C, goes higher than 2/3 V, threshold input pin 6 will cause the output voltage (pin 3) to go low and the discharge output (pin 7) shorts to pin 1. When the voltage on C, goes below 1/3 V, the trigger input (pin 2) will cause the output voltage to go high, and the short between the discharge output and pin I is removed, i.e., the discharge output is turned off. In the operation of this circuit, assuming that the voltage on capacitor C, has dropped to 1/3 V, the output voltage at pin 3 is then high, and the discharge output (pin 7) is turned off.Then C, will charge through variable resistor R, and diode D, with a time constant R,C,.When the voltage on C, reaches 2/3 V, the output voltage will go low, and pin 7 is shorted to pin 1, resulting in discharge of capacitor C, through variable resistor R2 and pins 7 and 1 with a time constant R2C1. When the voltage on C, reaches 1/3 V, the cycle begins again.

The timing network associated with IC2 forms a monostable multivibrator. When the output voltage of IC, (pin 3) goes low, a negative pulse is applied through capacitor C2 to the trigger input (pin 2) of IC2. This causes the output of IC2 to go high and pin 7 to turn off. Then capacitor C3 begins charging from zero volts through resistor R3 with a time constant R3C3. When the voltage on C3 reaches 2/3 V, the output voltage goes low, and C3 discharges through pins 7 and 1. The output then remains low until another trigger pulse is received from IC1. The output pulse is then differentiated by capacitor C4 and the negative transition of this output pulse is amplified and inverted by transistor Q2. This pulse is applied to the gate of SCR 7, as shown in Figure 8, to turn on the SCR.

The timing operation in terms of the waveforms shown in Figure 6 is such that at time to, IC, goes high, turning on transistor switch 5. At time t1, IC, goes low, turning off switch 5 and triggering IC2. At time t2, IC2 turns off (goes low), causing SCR switch 7 to be triggered on. A broad pulse is produced by IC, between time to and time t1, such as shown characterizing the switch drive current in Figure 6, and a narrow pulse (not shown) is produced by the action of IC2 at time t2 to gate the SCR on. After some time delay, IC, again goes high, thus beginning a new cycle.

Figure 7 shows a modification of the Figure 5 circuit wherein a secondary induction coil winding L3 is magnetically coupled to inductor L2, and SCR 7 is connected across inductor L3, forming a loop in which current I3 flows. The operation of this circuit is otherwise essentially the same as that described in connection with the Figure 1 embodiment.

By virtue of the modified arrangement, the SCR switch 7 is isolated from the power circuit while being magnetically coupled to inductor L2, and this permits a choice of the voltage and current ratings of the SCR.

Terminal A, of the SCR 7-L3 loop in Figure 7 may be connected if desired, to terminal A2 or other point on the power circuit for purposes of simplifying the control circuit connections, or for other reasons.

In a typical circuit such as those illustrated, inductor Ll would have an inductance of 100 millihenries, inductor L2 an inductance of 7 millihenries, the turns ratio of L3 to L2 would be 1.5 to i, and lamp 1 would be a 150 watt high pressure sodium vapor lamp as described hereinbefore.

While an independent DC voltage supply V, which may typically be about 15 volt, is shown connected to the control circuit in Figure 8, it will be understood that, if desired, the control circuit may be connected to the DC supply of the power circuit, with the provision of suitable means for reducing the voltage.

While particular types of controlled switches 5 and 7 are shown and described, it will be understood that other types of controlled switches may be employed for either or both of these components, as appropriate.

Referring now to the third form of the present invention and the drawings therefore, particularly to Figure 9, there is shown a circuit diagram illustrating an embodiment of the DC pulsing circuit of the invention for operating a gaseous discharge lamp 1, which is typically a high pressure sodium vapor lamp such as described above.

The circuit comprises terminals 2 of a source of alternating current and induction coil Ll connected at one side to one of the source terminals and at the other side to an input terminal of full wave bridge rectifier 3 which comprises diodes Dl, D2, D3 and D4 arranged in conventional manner as shown, the other input terminal of rectifier 3 being connected to the other source terminal 2.

Filter capacitor 4 connected across the DC supply circuit provides a filtered DC voltage supply for the pulsing circuit described hereinafter and increases the average voltage supplied thereto. Induction coil LI serves to limit the current to the lamp at the starting and warm-up stage.

The pulsing circuit illustrated in Figure 9 comprises lamp 1 connected in series with primary winding L2 of transformer 6 and transistor 5 across the DC power supply constituted by filter capacitor 4. Diode 7 is connected in series with transformer secondary winding L3 across the power supply. As indicated in the drawing, the primary winding and the secondary winding are arranged or connected so as to be out of phase with one another.

Transistor switch 5 is operated repetitively by timing (control) circuit 9 connected to the base and emitter of transistor 5 as shown, the details of control circuit 9 being depicted in Figure 11.

In the operation of the described circuit, and with reference to the waveform diagrams of Figure 10, when switch 5 closed at time to, a current I, begins to flow through lamp 1 and transformer primary L2. This current increases with a time constant L/R where L is the inductance of primary winding L2 and R is the effective resistance of lamp 1. At time t1, switch 5 opens, thereby interrupting current flow through the lamp and winding L2. At this time, there is energy stored in the magnetic field produced by the transformer current, the amount of energy being 1/2 LIp2, where Ip is the peak current through the transformer.

This energy should either be stored in the circuit or dissipated in lamp 1, since to dissipate it elsewhere would decrease the efficiency of the lamp operating circuit. In accordance with the invention, this energy is stored by transferring it to the power supply, i.e. capacitor 4 in the illustrated circuit, in the manner described below.

When switch 5 opens at time t1, the magnetic field in transformer 6 begins to collapse, generating a voltage on both the primary and secondary windings. This voltage is of such polarity that when the voltage on secondary winding L3 exceeds the voltage on capacitor 4, a current I2 will flow. Current I2 is initiated at some high value Ip' (see Figure 10), such that NsIp'=NpIp, where Ns and Np denote the number of turns on the secondary and primary windings respectively. Current I2 decays as the energy is transferred from secondary winding L3 to capacitor 4.

When switch 5 is closed, and with current I, flowing and the polarity as shown, diode 7 is reverse biased. When switch 5 opens, current I, is interrupted, generating a voltage across windings L2 and L3, which are tightly magnetically coupled. The provision of a reverse current I2 to the power supply in accordance with the invention not only contributes to producing a desirable waveform of current to the lamp as described below, but also avoids the generation of excessively high voltages in the circuit.

As a result of the described operation, the current pulses to lamp 1, as indicated by the waveform of current Ii in Figure 10, are characterized by a rapid rise and fall, which is particularly desirable in order to provide a substantial increase in color temperature of the gaseous discharge lamp, in accordance with the principles disclosed in our aforementioned U.K. patent application No. 1220/77, (Serial No. 1,575,831). At the same time, there is thus provided a highly efficient lamp ballast system which results in a high level of lamp system efficacy (lumens per watt).

Figure 11 is a circuit diagram of control circuit 9 shown in Figure 9, wherein the control circuit has output terminal A connected to the base of transistor 5 and output terminal B connected to the emitter of the transistor. The function of control circuit 9 is to produce a base drive current in transistor 5 for closing that switch and to remove the base drive current to open the switch, the base drive being produced between terminals A and B. For a lamp pulse repetition rate of 1 kHz, a typical timing for operation of transistor 5 (see Figure 10) when to=0 would be t,=200 microseconds.

The control circuit shown in Figure 11 comprises a timing network consisting of a 555 type integrated circuit (IC) and associated circuitry. An example of such an integrated circuit is type NE555 available commercially from Signetics Corporation.

The pins indicated for the illustrated IC circuit have the following functions:pin I is the power supply common (negative) voltage, pin 2 is the trigger input, pin 3 is the output voltage, pin 4 is the reset input, pin 6 is the threshold input, pin 7 is the discharge output, and pin 8 is the positive power supply input. The IC consists of a bistable circuit whose output voltage is either high (near positive power supply voltage) or low (near common or negative power supply voltage). The circuit is triggered into the high state when the voltage at trigger pin 2 goes below 1/3 V, where V is the power supply voltage. The circuit is triggered into the low state when the voltage at the threshold pin 6 goes above 2/3 V. The discharge pin 7 exhibits a short circuit to power supply common (pin 1) when the circuit is in the low state.

The timing network associated with IC forms an astable multivibrator. It will be noted that pins 2 and 6 are both connected to timing capacitor C,. Thus, when the voltage on C, goes higher than 2/3 V, threshold input pin 6 will cause the output voltage (pin 3) to go low and the discharge output (pin 7) shorts to pin 1. When the voltage on C, goes below 1/3 V, the trigger input (pin 2) will cause the output voltage to go' high, and the short between the discharge output and pin 1 is removed, i.e., the discharge output is turned off. In the operation of this circuit, assuming that the voltage on capacitor C, has dropped to 1/3 V, the output voltage at pin 3 is then high, and the discharge output (pin 7) is turned off. Then C, will charge through variable resistor R, and diode D, with a time constant R,C1.When the voltage on C, reaches 2/3 V, the output voltage will go low, and pin 7 is shorted to pin 1, resulting in discharge of capacitor C, through variable resistor R2 and pins 7 and I with a time constant R2C,. When the voltage on C, reaches 1/3 V, the cycle begins again.

The timing operation (see Figure 10) is such that at time to, IC goes high, turning on transistor switch 5. At time t1, IC goes low, turning off switch 5, thus producing a current pulse between to and t,. The cycle is repeated, beginning at time t3. The time interval to to t, is determined by the time constant R,C, and the time interval t, to t3 is determined by the time constant R2C,.

Figure 9a shows a modification of the Figure 9 circuit wherein the lamp is located in the main supply line in series between the DC supply and the junction of the parallel branches containing the transformer primary and secondary windings, respectively. In such arrangement the pulses applied to the lamp during operation will have a waveform characterized by a composite of the waveforms for I, and I2 as shown in Figure 10.

Figure 9b shows another modification of the circuit wherein the lamp is located in the secondary winding branch in series with L3 and diode 7. In this case, the waveform of the lamp current will be like that shown for I2 in Figure 10.

In a typical circuit such as shown in Figure 9 and using a 150 watt sodium vapor lamp, inductor L1 would have an inductance 100 millihenries, capacitor 4 would be 100 microfarads, winding L would be 1.3 millihenries, and the turns ratio of L3 to L2 would be 1.5 to 1.

Although a particular type of controlled switch 5 is shown and described, it will be understood that other types of controlled switches may be employed for this component.

WHAT WE CLAIM IS:- 1. A circuit for operating a gaseous discharge lamp, comprising in combination, a direct current power source, controlled switching means connected to said power source, unidirectional conducting means connected to said power source, means for connecting the gaseous discharge lamp to said power source, inductive means connected to said controlled switching means, said unidirectional conducting means, said lamp connecting means and said power source and control means being coupled to said controlled switching means for repetitively operating said controlled switching means at predetermined intervals, so that dc pulses may be applied to said gaseous discharge lamp for operation thereof and whereby energy stored in the magnetic field associated with said inductive means when power is being delivered to said discharge lamp by said power source may be conserved in said circuit when power is not being delivered to said discharge lamp by said power source.

2. A lamp operating circuit as claimed in claim 1, wherein said controlled switching means includes first and second switch means where said first switching means is in a first circuit branch across said power source, said unidirectional conducting means is in a second circuit branch across said power source, said inductive means being a transformer having a primary winding in said first branch in series with said first controlled switch means and a secondary winding in said branch in series with said unidirectional conducting means said means for connecting a gaseous discharge lamp to said power source being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. voltage, pin 2 is the trigger input, pin 3 is the output voltage, pin 4 is the reset input, pin 6 is the threshold input, pin 7 is the discharge output, and pin 8 is the positive power supply input. The IC consists of a bistable circuit whose output voltage is either high (near positive power supply voltage) or low (near common or negative power supply voltage). The circuit is triggered into the high state when the voltage at trigger pin 2 goes below 1/3 V, where V is the power supply voltage. The circuit is triggered into the low state when the voltage at the threshold pin 6 goes above 2/3 V. The discharge pin 7 exhibits a short circuit to power supply common (pin 1) when the circuit is in the low state. The timing network associated with IC forms an astable multivibrator. It will be noted that pins 2 and 6 are both connected to timing capacitor C,. Thus, when the voltage on C, goes higher than 2/3 V, threshold input pin 6 will cause the output voltage (pin 3) to go low and the discharge output (pin 7) shorts to pin 1. When the voltage on C, goes below 1/3 V, the trigger input (pin 2) will cause the output voltage to go' high, and the short between the discharge output and pin 1 is removed, i.e., the discharge output is turned off. In the operation of this circuit, assuming that the voltage on capacitor C, has dropped to 1/3 V, the output voltage at pin 3 is then high, and the discharge output (pin 7) is turned off. Then C, will charge through variable resistor R, and diode D, with a time constant R,C1.When the voltage on C, reaches 2/3 V, the output voltage will go low, and pin 7 is shorted to pin 1, resulting in discharge of capacitor C, through variable resistor R2 and pins 7 and I with a time constant R2C,. When the voltage on C, reaches 1/3 V, the cycle begins again. The timing operation (see Figure 10) is such that at time to, IC goes high, turning on transistor switch 5. At time t1, IC goes low, turning off switch 5, thus producing a current pulse between to and t,. The cycle is repeated, beginning at time t3. The time interval to to t, is determined by the time constant R,C, and the time interval t, to t3 is determined by the time constant R2C,. Figure 9a shows a modification of the Figure 9 circuit wherein the lamp is located in the main supply line in series between the DC supply and the junction of the parallel branches containing the transformer primary and secondary windings, respectively. In such arrangement the pulses applied to the lamp during operation will have a waveform characterized by a composite of the waveforms for I, and I2 as shown in Figure 10. Figure 9b shows another modification of the circuit wherein the lamp is located in the secondary winding branch in series with L3 and diode 7. In this case, the waveform of the lamp current will be like that shown for I2 in Figure 10. In a typical circuit such as shown in Figure 9 and using a 150 watt sodium vapor lamp, inductor L1 would have an inductance 100 millihenries, capacitor 4 would be 100 microfarads, winding L would be 1.3 millihenries, and the turns ratio of L3 to L2 would be 1.5 to 1. While an independent DC voltage supply V, which may typically be about 15 volts, is shown connected to the control circuit in Figure 3, it will be understood that, if desired, the control circuit may be connected to the DC supply of the power circuit, with the provision of suitable means for reducing the voltage. Although a particular type of controlled switch 5 is shown and described, it will be understood that other types of controlled switches may be employed for this component. WHAT WE CLAIM IS:-

1. A circuit for operating a gaseous discharge lamp, comprising in combination, a direct current power source, controlled switching means connected to said power source, unidirectional conducting means connected to said power source, means for connecting the gaseous discharge lamp to said power source, inductive means connected to said controlled switching means, said unidirectional conducting means, said lamp connecting means and said power source and control means being coupled to said controlled switching means for repetitively operating said controlled switching means at predetermined intervals, so that dc pulses may be applied to said gaseous discharge lamp for operation thereof and whereby energy stored in the magnetic field associated with said inductive means when power is being delivered to said discharge lamp by said power source may be conserved in said circuit when power is not being delivered to said discharge lamp by said power source.

in series with at least one of said branches and where said second controlled switch means is coupled to said secondary winding for substantially stopping current flow to said unidirectional conducting means and for storing magnetic energy in said transformer while said second controlled switch means is on and said control means being coupled to both said first and second controlled switch means for repetitively operating same at said predetermined intervals, whereby DC pulses may be applied to the gaseous discharge lamp for operation thereof.

3. A circuit as claimed in claim 2, said second controlled switch means being connected across said secondary winding.

4. A circuit as claimed in claim 2, said transformer including a tertiary winding magnetically coupled to said secondary winding, said second controlled switch means being connected across said tertiary winding.

5. A circuit as claimed in Claim 2, said lamp connecting means being.in said first branch in series with said first controlled switch means and said primary winding.

6. A circuit as claimed in Claim 5, said primary winding being connected between said lamp connecting means and said first controlled switch means.

7. A circuit as claimed in Claim 2, said lamp connecting means being in said second branch-in series with said unidirectional conducting means and said secondary winding.

8. A circuit as claimed in Claim 2, said lamp connecting means being connected in series between said power source and the junction of said first and second branches.

9. A circuit as claimed in Claim 2, said first controlled switching means comprising a transistor having a base electrode, said sec6nd controlled switch means comprising a unidirectional controlled switch having a gate electrode, said control means connected to said base electrode and said gate electrode.

10. A circuit as claimed in Claim 9, said unidirectional controlled switch comprising a silicon controlled rectifier.

I I. A circuit as claimed in Claim 2, said control means having timing network means comprising first and second multivibrator circuits connected respectively to said first and second controlled switch means, said first multivibrator circuit connected to said second multivibrator circuit for controlling the operation thereof.

12. A circuit as claimed in Claim 11, said first multivibrator circuit comprising an astable multivibrator circuit and said second multivibrator circuit comprising a monostable multivibrator circuit

13. A circuit as claimed in Claim 2, and a gaseous discharge lamp connected to said lamp connecting means.

14. A circuit as claimed in Claim 13, said gaseous discharge lamp comprising a high pressure sodium vapor lamp.

15. A circuit as claimed in Claim 13, said gaseous discharge lamp comprising mixed metal vapors.

16. A circuit as claimed in Claim 2, said unidirectional conducting means comprising a diode.

17. A circuit as claimed in Claim 2, said unidirectional conducting means, said secondary winding and said second controlled switch means being arranged such that when said first controlled switch means is on, the current flows in one direction from said power source toward said first branch, and when said first and second controlled switch means are off the current flows in the opposite direction toward said power source from said second branch, and when said second controlled switch means is on, the current circulates in a loop comprising said second controlled switch means and a portion of said transformer.

18. A circuit as claimed in Claim 2, said primary winding and said secondary winding being arranged so as to be out of phase relative to one another.

19. A lamp operating circuit as claimed in claim 1 wherein said controlled switching means includes a first and second controlled switch means, said first controlled switch means and said inductive means connected in series across said power source, said means for connecting said lamp serially connecting said gaseous discharge lamp to said first controlled switch means and said inductive means, said unidirectional conducting means being connected across said series connected inductive means and said lamp connecting means, said second controlled switch means being coupled to said inductive means for stopping current flow to the gaseous discharge lamp and for storing magnetic energy in said inductance means while said second controlled switch means is on, and where said control means is coupled to said first and second controlled switch means for repetitively operating the same at said predetermined intervals, whereby DC pulses may be applied to the gaseous discharge lamp for operation thereof.

20. A circuit as claimed in claim 19, said inductive means and said unidirectional conducting means comprising with the lamp a discharge loop, said first controlled switch means connected between said power source and said discharge loop.

21. A circuit as claimed in claim 20, said inductive means comprising an induction coil connected in series between said first controlled switch means and said lamp connecting means, said second controlled switch means connected across said induction coil.

22. A circuit as claimed in Claim 20, said inductive means comprising a primary winding connected in series between said first controlled switch means and said lamp connecting means and a secondary winding magnetically coupled to said primary winding, said second controlled switch means connected across said secondary winding.

23. A circuit as claimed in Claim 19, said first controlled switch means comprising a transistor having a base electrode, said second controlled switch means comprising a unidirectional controlled switch having a gate electrode, said control means connected to said base electrode and said gate electrode.

24. A circuit as claimed in Claim 23, said unidirectional controlled switch comprising a silicon controlled rectifier.

25. A circuit as claimed in Claim 19, said control means having timing network means comprising first and second multivibrator circuits connected respectively to said first and second controlled switch means, said first multivibrator circuit connected to said second multivibrator circuit for controlling the operation thereof.

26. A circuit as claimed in Claim 25, said first multivibrator circuit comprising an astable multivibrator circuit and said second multivibrator circuit comprising a monostable multivibrator circuit.

27. A circuit as claimed in Claim 19, said unidirectional conducting means comprising a diode.

28. A lamp operating circuit as claimed in claim 1 in combination with a gaseous discharge lamp, wherein said controlled switching means includes a first and second controlled switch means, said first controlled switch means, said inductive means and said gaseous discharge lamp connected in series across said power source, said unidirectional conducting means being connected across said series connected inductive means and said gaseous discharge lamp, said second controlled switch means being coupled to said inductive means for stopping current flow to said gaseous discharge lamp and for storing magnetic energy in said inductive means while said second controlled switch means is on, said control means being coupled to said first and second controlled switch means for repetitively operating the same at said predetermined intervals, whereby DC pulses are applied to said gaseous discharge lamp for operation thereof.

29. A circuit as claimed in Claim 28, said gaseous discharge lamp comprising mixed metal vapors.

30. A circuit as claimed in Claim 28, wherein said gaseous discharge lamp is a high pressure sodium vapor lamp.

31. A circuit as claimed in Claim 30, said inductance means, said lamp, and said unidirectional conducting means comprising a discharge loop, said first controlled switch means connected between said power source and said discharge loop.

32. A circuit as claimed in Claim 31, said first controlled switch means comprising a transistor switch, said second controlled switch means comprising a silicon controlled rectifier.

33. A circuit as claimed in Claim 31, said inductive means comprising an induction coil connected in series between said first controlled switch means and said lamp, said second controlled switch means connected across said induction coil.

34. A circuit as claimed in Claim 31, said inductive means comprising a primary winding connected in series between said first controlled switch means and said lamp, and a second winding magnetically coupled to said primary winding, said second controlled switch means connected across said secondary winding.

35. A lamp operating circuit as claimed in claim 1, wherein said controlled switching means is across said power source, said inductive means is a transformer having a primary winding and a secondary winding, said primary winding being in series with said controlled switch means, said unidirectional conducting means being in series with said secondary winding across said power source, said means for connecting a gaseous discharge lamp connecting said discharge lamp in series with said controlled switch means and said primary winding, and where said control means is coupled to said controlled switch means for repetitively operating the same at said predetermined intervals, whereby DC pulses may be applied to the gaseous discharge lamp for operation thereof.

36. A circuit as claimed in claim 35, said primary winding being connected between said controlled switching means and said lamp connecting means.

37. A circuit as claimed in claim 35, said serially connected controlled switching means, lamp connecting means and primary winding forming a first branch across said power source, said serially connected unidirectional conducting means and secondary winding forming a second branch in parallel with said first branch.

38. A circuit as claimed in Claim 37, said unidirectional conducting means and said secondary winding being arranged such that when said controlled switching means is on, the current flows in one direction from said power source toward said first branch, and when said controlled switching means is off, the current flows in the opposite direction toward said power source from said second branch.

39. A circuit as claimed in Claim 35, said control means having timing network means comprising a multivibrator circuit connected to said controlled switching means.

40. A circuit as claimed in Claim 35, said controlled switching means comprising a transistor having a base and an emitter, said control means connected to said base and said emitter.

41. A circuit as claimed in Claim 38, said unidirectional conducting means comprising a diode.

42. A circuit as claimed in Claim 38, including a gaseous discharge lamp connected in said first branch in series with said controlled switch means and said primary winding.

43. A circuit as claimed in Claim 42, wherein said gaseous discharge lamp is a high pressure sodium vapor lamp.

44. A circuit as claimed in Claim 42, said gaseous discharge lamp comprising mixed metal vapors.

45. A circuit as claimed in Claim 42, said primary winding being connected between said gaseous discharge lamp and said controlled switching means.

46. A circuit as claimed in claim 37, said primary winding and said secondary winding being arranged so as to be out of phase relative to one another.

47. A lamp operating circuit as claimed in claim 1, wherein a first branch includes said controlled switching means across said power source, a second branch includes said unidirectional conducting means across said power source said inductive means being a transformer having a primary winding in said first branch in series with said controlled switch means a secondary winding in said second branch in series with said unidirectional conducting means, said means for connecting a gaseous discharge lamp to said power source connecting said lamp in series with at least one of said branches, and where said control means is coupled to said controlled switching means for repetitively operating the same at said predetermined intervals, whereby DC pulses may be applied to the gaseous discharge lamp for operation thereof.

48. A circuit as claimed in Claim 47, said lamp connecting means being in said first branch in series with said controlled switching means and said primary winding.

49. A circuit as claimed in Claim 47, said lamp connecting means being in said second branch in series with said unidirectional conducting means and said secondary winding.

50. A circuit as claimed in Claim 47, said lamp connecting means being connected in series between said power source and the junction of said first and said second branches.

51. A lamp operating circuit substantially as hereinbefore described with reference to and as shown in the accompanying drawings.