EP1326484B1 - Apparatus for operating discharge lamps - Google Patents

Abstract

The device has a half-bridge inverter with transistors (T1,T2) and a load circuit coupling between the transistors includes a primary transformer winding via which a load current flows. Drive circuits (1,2) of transistors includes an integration unit that switches off the transistor on reaching a preset value, and two voltage threshold value switches, where a threshold of one switch is less than that of other switch.

Description

Technical area

The invention relates to a control gear for gas discharge lamps according to the preamble of claim 1. It is in particular an improvement of the half-bridge inverter contained in the operating device and its control. Furthermore, the invention deals with the simplification of a switch-off device of the operating device and a cost-effective power factor correction of the current absorbed by the network.

State of the art

Document EP 0 481 077 A2 (Schmitt) discloses a circuit arrangement for operating a lamp. The circuit arrangement comprises a half-bridge inverter with MOSFETs. The drive signals for the MOSFETs are derived from a respective additional winding, which are applied to a lamp inductor. To set the oscillation condition, drive circuits for the MOSFETs each contain an LC parallel resonant circuit. In embodiments, the drive circuits also include Zener diodes. They are used to shorten the on-time of the MOSFETs or for overvoltage protection.

The document EP 1 001 662 (Nerone) describes a half-bridge circuit with complementary MOSFETs. To control the resonance of the load circuit during the ignition of a connected gas discharge lamp Zener diodes are connected in parallel with the drive electrodes of the MOSFETs for limiting the voltage.

The document EP 0 093 469 (De Bijl) describes an operating device for gas discharge lamps, which represents the state of the art. This operating device includes a self-oscillating half-bridge inverter, which generates a high-frequency alternating voltage from a DC voltage by alternately switching on and off an upper and a lower series-connected half-bridge transistors. The DC voltage is usually generated by means of a bridge rectifier, consisting of four rectifier diodes, from the mains voltage. Self-oscillating in this context means that the control of the half-bridge transistors is obtained from a load circuit and no independently oscillating oscillator circuit is provided for generating said drive. Preferably, said drive is obtained by means of a current transformer. A primary winding of the current transformer is arranged in the load circuit and is of a Load current flows through, which can be set equal to the current that is emitted by the half-bridge inverter substantially. Each secondary winding of the current transformer is arranged in two drive circuits, each of which generates a signal which is supplied to the control electrodes of the half-bridge transistors. The load circuit is connected to the junction of the half-bridge transistors. The main component of the load circuit is a lamp choke, to which gas discharge lamps can be connected in series via terminal connections. It is also possible to switch several load circuits in parallel; The primary winding must then be arranged in such a way that it flows through the sum of all load circuits.

In the drive circuits in each case a feedback signal is generated which is substantially proportional to the load current. For this purpose, the secondary windings ideally have to be short-circuited, in practice low-resistance terminated. Otherwise, either saturation phenomena occur in the current transformer, or the primary winding exerts an undesirably large influence on the load circuit. In the prior art bipolar transistors are used for the half-bridge transistors, which receive their control from the secondary windings. The base terminal of the bipolar transistors, which is used as a control electrode is naturally low enough to o. G. To avoid effects.

The voltage drop across the secondary windings is below the o.g. Conditions a measure of the load current and forms in the prior art feedback signals. These are each supplied to a timer, which consists in the simplest case of the series connection of a time capacitor and a time resistor. If the respective time capacitor is charged to an integration value which is sufficient to trigger a turn-off transistor, the respective half-bridge transistor is switched off.

In particular for igniting the gas discharge lamps, a resonant capacitor is connected in series with the lamp inductor and acting in parallel with a gas discharge lamp, which resonant circuit forms a resonant circuit with the lamp inductor. This is operated to ignite near its resonance, which forms a sufficiently high voltage to ignite a gas discharge lamp at the resonance capacitor.

Accordingly, a high current is formed in the lamp inductor and thus in the half-bridge transistors. In order to avoid overloading of components, the amplitude of the load current is limited in the prior art. This is done via a respective first voltage threshold, which is connected in parallel to the respective time resistor. If the load current rises above a predetermined level, then the respective feedback signal reaches a value which causes the respective first voltage threshold value switch to break and thus leads to the instantaneous switching-off of the respective half-bridge transistor.

Presentation of the invention

It is an object of the present invention to provide a control gear for gas discharge lamps according to the preamble of claim 1, which makes the topology shown in the prior art not only for half-bridges with bipolar transistors, which naturally require a drive current feasible, but also voltage-controlled semiconductor switches such as MOS Field effect transistors (MOSFET) can be used. The problem underlying this problem essentially involves the provision of a driving signal for the semiconductor switches, which is proportional to the load current.

This object is achieved by a control gear for gas discharge lamps having the features of the preamble of claim 1 by the features of the characterizing part of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

Mostly for cost reasons, bipolar transistors are increasingly being used by voltage-controlled semiconductor switches, e.g. Replaced MOSFET and IGBT.

If a voltage-controlled semiconductor switch is actuated with one of the secondary windings described above instead of a bipolar transistor, then the termination of the secondary winding is no longer low-ohmic, but rather high-resistance, and the disadvantages mentioned in the section on the prior art are reached. According to the invention The drive circuits are each equipped with a second voltage threshold, which has a second voltage threshold and comes to lie in a parallel circuit to the secondary winding. In the simplest case, the second voltage threshold consists of the series connection of a Zener diode and a current measuring resistor, wherein the Zener diode has a Zener voltage which corresponds to the second voltage threshold. If the voltage at the secondary winding rises starting at zero, the second voltage threshold value switch is initially inoperative. Upon reaching the second voltage threshold, the zener diode begins to conduct and closes the secondary winding as desired from low impedance. The value of the second voltage threshold must be lower than a threshold voltage which the voltage-controlled semiconductor switch at least requires as drive. When dimensioning the current sense resistor, two conditions must be met. On the one hand, the value of the current measuring resistor must be small enough so that a low-impedance termination of the secondary winding is ensured. On the other hand, the value of the current sense resistor must be large enough so that the voltage at the secondary winding can continue to rise up to the first voltage threshold.

Since, according to the invention, a current which is essentially proportional to the load current flows in the current measuring resistor, the voltage at the current measuring resistor is naturally also a measure of the load current. The voltage at the current measuring resistor can thereby be used according to the invention for the detection of a fault. It is fed to a shutdown device. In order to suppress interference, the time average of the voltage at the current measuring resistor is formed in the turn-off device. If this exceeds a given limit value, the turn-off device prevents a further oscillation of the half-bridge inverter. This happens in particular by suppression of the drive signal of one of the two half-bridge transistors.

The operating devices in question generally have two mains voltage terminals which can be connected to a mains voltage, whereby a mains current can flow. Relevant standards (eg: IEC 1000-3-2) write maximum amplitudes for the harmonics of the mains current. To comply with these standards, operating devices have so-called PFC circuits (Power Factor Correction). A cost-effective implementation of these PFC circuits represent so-called. Pump circuits, as z. B. in EP 253 224 (breeding bars) or EP 1 028 606 (Rudolph) are described. In the combination of a pump circuit with a self-oscillating half-bridge inverter according to the prior art, there are problems in generating the necessary ignition voltage for the gas discharge lamps and by high power dissipation when switching the half-bridge transistors. Especially with high power for the gas discharge lamps, the problems mentioned occur. One reason for this is, among other things, storage times which are typical for bipolar transistors and do not allow an exact setting of the switch-off time. The present invention allows the use of voltage-controlled semiconductor switches such as MOSFETs, which have no storage times and therefore the aforementioned problems can be avoided. This means that the half-bridge inverter according to the invention, in combination with a pump circuit, can advantageously also be used for a load that consumes a power of more than 100W.

Another effect which occurs in the half-bridge inverter according to the invention with pump circuit is the strong modulation of the operating frequency by the mains voltage, which has the oscillation of the half-bridge inverter. Depending on the instantaneous value of the mains voltage, said operating frequency is within a frequency band having a bandwidth of more than 10 kHz. Thus, the electromagnetic interference caused by an operating device according to the invention is distributed over a wide frequency band. Thus, the energy that hits a faulty device, advantageously low. In addition, the effort for the suppression of a control gear according to the invention can be kept low.

A further advantageous use of the current measuring resistor according to the invention is given in the starting circuit of the self-oscillating half-bridge inverter. To start the half-bridge inverter, it is customary to charge a start capacitor and, upon reaching a trigger voltage at the charging capacitor, a portion of the charge stored in the charging capacitor via a trigger element to the control electrode of a half-bridge capacitor to discharge. In this case, the problem may arise that the charge pulse generated in this way at the relevant control electrode is too short and too low and no sustained oscillation of the half-bridge inverter is triggered. According to the invention, a portion of the stored charge of the charging capacitor is supplied via a diode to the current measuring resistor according to the invention. This makes it possible to achieve a reliable oscillation of the half-bridge inverter.

Description of the drawings

Figur 1

die Grundschaltung des erfindungsgemäßen Betriebsgeräts

Figur 2

ein Ausführungsbeispiel einer erfindungsgemäßen Ansteuerschaltung

Figur 3

ein Ausführungsbeispiel eines erfindungsgemäßen Betriebsgeräts mit Pumpschaltung

Figur 4

ein Ausführungsbeispiel für eine erfindungsgemäße Abschalteinrichtung

In the following, the invention will be explained in more detail with reference to embodiments. Show it:

FIG. 1

the basic circuit of the operating device according to the invention

FIG. 2

An embodiment of a drive circuit according to the invention

FIG. 3

An embodiment of an operating device according to the invention with pump circuit

FIG. 4

an embodiment of a shutdown device according to the invention

In the following, resistors are denoted by the letter R, transistors by the letter T, diodes by the letter D, capacitors by the letter C, and terminals by the letter J each followed by a number.

FIG. 1 shows the basic circuit of a control gear according to the invention. The operating device can be connected to a mains voltage via terminals J1, J2. The mains voltage is fed to a block FR. This includes well-known filter and rectifier devices. The filter devices have the task to suppress interference. The rectifier device usually consists of a bridge rectifier consisting of four diodes. With the aid of the rectifier device, a DC voltage is supplied to a half-bridge inverter HB. The half-bridge inverter essentially comprises the series connection of an upper semiconductor switch T1 and a lower semiconductor switch T2, which are voltage-controlled according to the invention. The exemplary embodiment in FIG. 1 is realized with N-channel MOSFET. However, it is also possible to use, for example, IGBT or P-channel MOSFETs. In the N-channel MOSFET used in Figure 1, it is necessary that the positive output of the rectifier device is supplied via a node 3 to the upper transistor T1, while the negative output of the rectifier device is connected to the ground potential M. The same polarity applies to commercial IGBTs. Reverse polarity must be when using P-channel MOSFET.

Between the node 3 and the ground potential M, a storage capacitor Cl is connected, which caches energy from the mains voltage before it is delivered to a lamp Lp.

For driving the half-bridge transistors T1, T2, the half-bridge inverter HB contains a drive circuit 1, 2 for each half-bridge transistor T1, T2. The drive circuits 1, 2 are each connected via a terminal A to the respective gate terminal and via a terminal B to the respective source terminal. Connected to the respective half-bridge transistor. The drive circuit 2 for the lower half-bridge transistor T2 has a third terminal S, to which a turn-off device can be connected.

The junction of the half-bridge transistors T1, T2 forms a node 4, to which a load circuit is connected. A second terminal of the load circuit is connected in Figure 1 to the ground potential M. Gleichwirkend the second terminal of the load circuit can alternatively be connected to the node 3. The load circuit consists essentially of the series connection of a primary winding L2 of a current transformer, a lamp inductor L1, a resonance capacitor C2 and a coupling capacitor C3. Parallel to the resonant capacitor C2, one or more lamps Lp connected in series can be connected via the lamp terminals J3, J4. In the exemplary embodiment, a preheating of the lamp filaments is not provided. However, those skilled in the art are generally familiar devices for filament heating available, which he can use with the operating device according to the invention. It is also possible to operate several parallel-connected load circuits. The function of the individual elements of the load circuit can be taken from the prior art.

FIG. 2 shows a preferred exemplary embodiment of a drive circuit according to the invention. A secondary winding L3 of the current transformer is connected between a node 20 and the connection B known from FIG. A diode D1 lies with its anode at the node 20 and with its cathode at a node 21. Via a resistor R3, the node 21 is connected to the connection A known from FIG. Connected in parallel with the secondary winding L3 is an integrating element which is designed as a series connection of a time resistor R1 and a time capacitor C4 and has an integration constant which corresponds to the product of the values of R1 and C4. The junction of R1 and C4 forms a node 22. Parallel to C4, an integration value is tapped and applied to the control electrode of a semiconductor switch T3. The switching path of the semiconductor switch T3 is located between the terminals A and B. In parallel, as in the embodiment, to increase the switching reliability, a resistor R4 are connected. Preferably, the semiconductor switch T3 is designed as a small-signal bipolar transistor.

Between node 21 and node 22, a first voltage threshold is switched to a first voltage threshold. It is designed as a zener diode D3. If the voltage fed into the drive circuit by L3 exceeds a value which results in exceeding the zener voltage of D3, then the time capacitor C4 is charged not only via the time resistor R1 but also via D3, thereby reducing the integration constant of the integrator.

Between the node 21 and the terminal B, a second voltage threshold value switch is connected according to the invention with a second voltage threshold. It is preferred as a series circuit of a Zener diode D2 and a current measuring resistor R2 executed. When the voltage at L3 rises, the associated half-bridge transistor is first of all driven via terminal A. After further increase of the voltage at R2, the zener voltage of D2 is exceeded according to the invention. This results in a current flow through the current measuring resistor R2, which is substantially proportional to the load current in the load circuit. This prevents saturation of the current transformer and achieves a load current-proportional charge of the integration element. If the current in the load circuit is so large that the zener voltage of D3 is exceeded, then the associated half-bridge transistor shuts down quickly.

At the junction between D2 and the current measuring resistor R2, a terminal S is led out. With respect to terminal B, a voltage proportional to the load current can be taken from it. This can be supplied to a shutdown device as explained below. Since the voltages in the turn-off device are generally related to the ground potential M, only the drive circuit associated with the lower half-bridge transistor has a terminal S.

The following table summarizes the preferred dimensions of components shown in FIG. module value D2 5.6V D3 22V R1 1,8kΩ R2 27Ω R3 220Ω R4 2,2kΩ C4 10nF

In FIG. 3, the half-bridge inverter HB according to the invention, as described in FIGS. 1 and 2, is realized in an operating device with a pump circuit. In contrast to Figure 1, the positive output of the rectifier device in the block FR is not directly connected to the node 3, but via two parallel connected series circuits of two diodes. A first diode series circuit with a first diode junction, the diodes D5 and D6 form. A second diode series circuit with a second diode connection point form the diodes D4 and D7. Various nodes of the load circuit known from FIG. 1 are connected to the diode connection points via reactance double poles.

The lamp terminal J3 is connected to the first diode connection point via a pumping capacitor C6. The lamp terminal J3 is distinguished from the lamp terminal J4 in that the value of the amplitude of its AC component is larger than the ground potential. The resonance capacitor C2 from FIG. 1 is omitted. Its function is taken over by the pump capacitor C6.

The connection point of the primary winding L2 and the lamp inductor L1 is connected via the series circuit of a pumping inductor L4 and a capacitor C7 to the second diode connection point. The pump inductor L4 can also be connected directly to the node 4 known from FIG. 1, which represents the connection point of the half-brittle transistors T1 and T2. The capacitor C7 essentially serves to block a DC component in the current through the pumping inductor L4.

The node 4 known from FIG. 1 is connected to the first diode connection point via a second pump capacitor C5.

FIG. 3 shows a pump circuit structure with three so-called pump branches: one pump branch is represented by the pump capacitor C6, another by the second pump capacitor C5 and a third by the pump choke L4. Each pump branch in itself already has an effect as a PFC circuit, so that not always necessarily all three pump branches must be present. Rather, any combination of pumping branches is possible.

Another possible variation relates to the diodes D5 and D7. These diodes can also take over functions that are assigned to the rectifier device in block FR. Corresponding diodes in the rectifier device can then be omitted.

FIG. 4 shows how the current measuring resistor R2 according to the invention and the connection S connected thereto from FIG. 2 can be advantageously used for a switch-off and a starting device of the operating device.

The shutdown device includes a well-known thyristor replica consisting of the resistors R42, R43, R44 and R45 and the transistors T41 and T42. The thyristor replica is connected via a resistor R41 to the node 3 of FIG. The other end of the thyristor reproduction is at ground potential M.

A voltage divider consisting of resistors R46 and R47 supplies a voltage which is proportional to the load current via terminal S. The voltage divider divides the supplied voltage to a value which normally does not cause the operating device to be switched off. By a capacitor C40, which is fed by the voltage divider, the time average of the load current is formed and provided in the form of a reference to the ground potential voltage. This voltage is supplied to the control electrode of a semiconductor switch, which is designed as a bipolar transistor T43. If the mean value of the load current exceeds a specified value in the event of a fault, the thyristor simulation is triggered via the collector connection of T43. Thereby, a terminal G2, which is connected to the control electrode of the lower half-bridge transistor, connected to the ground potential M via a diode D42. This prevents further oscillation of the half-bridge inverter.

The start of the oscillation of the half-bridge inverter is done by means of a well-known starting capacitor C41, which is charged via the resistor R41 from the mains voltage. Connected to C41 is a trigger diode D40 (DIAC). When the voltage at C41 reaches the trigger voltage of the trigger diode D40, the control electrode of the lower half-bridge transistor is supplied with a start pulse via a diode D41 and the terminal G2. In practice, this start pulse is too short and no reliable starting of the oscillation of the half-bridge inverter takes place. Advantageously, therefore, the terminal S is used: Via a diode D43, the terminal S according to the invention with the trigger diode D40 connected. The start pulse is not only via the diode D41, but also according to the invention via the diode D43 and on the diode D2 and the resistor R3 of Figure 2. Thus, the start pulse is extended and increases what leads to a safe start of the oscillation of the half-bridge inverter.

Claims (8)

1. Operating device for operating gas discharge lamps, having the following features:

   • a free-running half-bridge inverter (HB) which contains two half-bridge transistors (T1, T2) connected in series,

   • a load circuit which is connected to the connection point between the half-bridge transistors (4) and which contains a primary winding (L2) of a current transformer through which a load current flows which is drawn from the half-bridge inverter (HB),

   • in each case one drive circuit (1, 2) for each half-bridge transistor (T1, T2), which in each case contains the following components:

   - a secondary winding (L3) of the current transformer,

   - an integration element (R1, C4) which essentially integrates the voltage across the secondary winding (L3) of the current transformer and switches off the relevant half-bridge transistor on reaching a predetermined integration value,

   - a first voltage threshold value switch (D3), which reduces the integration constant of the integration element on reaching a given first voltage threshold,

   characterized in that

   • the half-bridge transistors (T1, T2) are voltage controlled transistors, and

   • at least one drive circuit (1, 2) has a second voltage threshold value switch (D2, R2) with a second voltage threshold which is lower than the first voltage threshold, with the second voltage threshold value switch (D2, R2) being connected in parallel with the secondary winding (L3), and

   • the value of the second voltage threshold is lower than a threshold voltage which the half-bridge transistors (T1, T2) require, as a minimum, as a drive.
2. Operating device according to Claim 1, characterized in that the second voltage threshold value switch contains a zener diode (D2) and a current measurement resistor (R2) connected in series.
3. Operating device according to Claim 2, characterized in that the voltage across the current measurement resistor (R2) is supplied to a switching-off device, which evaluates the time mean value or the instantaneous value of this voltage and, if a given limit value is exceeded, prevents further oscillation of the half-bridge inverter (HB).
4. Operating device according to Claim 1, characterized in that the operating device has two mains voltage terminals (J1, J2), which can be connected to a mains voltage, and power factor correction for a mains current flowing via the mains voltage terminals (J1, J2) is achieved by means of a pumping circuit.
5. Operating device according to Claim 4, characterized in that the pumping circuit has the following features:

   • a portion of the mains current flows via a first pumping diode (D5) which, with a second pumping diode (D6), forms a first diode series circuit having a first diode connection point, with the diodes being connected such that they allow current to flow from the mains terminals to the half-bridge inverter (HB),

   • the operating device has at least two lamp terminals (J3, J4), which can be connected to lamp connections, with one lamp terminal (J3) being connected to the first diode connection point via a pumping capacitor (C6).
6. Operating device according to Claim 5, characterized in that the pumping capacitor (C6) is connected to that lamp terminal (J3) which, with respect to a reference earth potential (M), is at a voltage which has the maximum value for the AC voltage component in comparison to the voltage at the other lamp terminals (J4).
7. Operating device according to Claim 5, characterized by the following features:

   • a second diode series circuit formed by two diodes (D4, D7) is connected in parallel with the first diode series circuit, thus forming a second diode connection point, with the diodes (D4, D7) being connected such that they allow current to flow from the mains to the half-bridge inverter (HB),

   • the second diode connection point is connected at least via a pumping inductor (L4) to the connection point (4) of the half-bridge transistors (T1, T2).
8. Operating device according to Claim 2, characterized in that the operating device contains a starting capacitor (C41), which is connected to the current measurement resistor (R2) via a trigger diode (D40) and a diode (D43) connected in series.

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