EP1326484A2 - 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 field

The invention relates to an operating device 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 control gear and its Control. Furthermore, the invention deals with the simplification of a shutdown device of the control gear and an inexpensive power factor correction of the electricity consumed by the grid.

State of the art

In the document EP 0 093 469 (De Bijl) there is an operating device for gas discharge lamps described, which represents the prior art. This control gear contains one self-oscillating half-bridge inverter, which consists of a DC voltage high frequency AC voltage is generated by an upper and a lower in series switched half-bridge transistors can be switched on and off alternately. The DC voltage is mostly with the help of a bridge rectifier consisting of four Rectifier diodes, generated from the mains voltage. Self-swinging means in this connection that the control of the half-bridge transistors from one Load circuit is gained and no independently oscillating oscillator circuit is provided to generate said control. The is preferred said control obtained with the help of a current transformer. A Primary winding of the current transformer is arranged in the load circuit and is from flowed through a load current, which are essentially equated to the current Flowed through the load current, which can essentially be equated to the current, which the half-bridge inverter delivers. One secondary winding each of the current transformer is arranged in two control circuits, each with a signal generate, which is supplied to the control electrodes of the half-bridge transistors. The Load circuit is connected at the junction of the half-bridge transistors. The main component of the load circuit is a lamp choke, to which via terminal connections Gas discharge lamps can be connected in series. It is also possible to connect several load circuits in parallel; the primary winding should then be arranged that the sum of all load circuits flows through it.

In the control circuits, a feedback signal is generated which corresponds to the Load current is substantially proportional. To do this, the secondary windings ideally short-circuited, in practice low-impedance. Otherwise, either appear in the current transformer, or the primary winding has an undesirably large influence on the load circuit. According to the prior art, bipolar transistors are used for the half-bridge transistors used, which get their control from the secondary windings. The base connection of the bipolar transistors, which is used as the control electrode is of course low-impedance enough to Avoid effects.

The voltage drop at the secondary windings, represents under the above conditions is a measure of the load current and forms feedback signals in the prior art. These are each fed to a timer, which in the simplest case comes from the series connection a time capacitor and a time resistor. Is the respective one Time capacitor charged to an integration value that is sufficient to one To control the turn-off transistor, the respective half-bridge transistor is turned off.

In particular for the ignition of the gas discharge lamps is serial to the lamp choke and a resonance capacitor connected in parallel to a gas discharge lamp, which forms a resonant circuit with the lamp choke. This becomes Ignition operated near its resonance, causing itself to resonate at the capacitor a voltage high enough to ignite a gas discharge lamp is formed.

Accordingly, forms in the lamp choke and thus in the half-bridge transistors a high current out. To avoid overloading components, the amplitude of the load current is limited in the prior art. This happens via a first voltage threshold switch, which is parallel to the respective time resistor is switched. If the load current rises above a predetermined one Dimension, the respective feedback signal reaches a value that corresponds to the respective can break through the first voltage threshold switch and thus to the immediate Turning off the respective half-bridge transistor leads.

Presentation of the invention

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

This task is performed by an operating device for gas discharge lamps Features of the preamble of claim 1 by the features of the characterizing Part of claim 1 solved. Find particularly advantageous configurations themselves in the dependent claims.

Mostly for reasons of cost, bipolar transistors are increasingly being controlled by voltage Semiconductor switches such as MOSFET and IGBT replaced.

Use one of the secondary windings described above instead of a bipolar transistor a voltage controlled semiconductor switch is controlled, so the conclusion the secondary winding is no longer low-resistance, but high-resistance and the Disadvantages mentioned in the section on the prior art arise. According to the invention the control circuits each have a second voltage threshold switch equipped, which has a second voltage threshold and in a parallel connection to the secondary winding comes to rest. In the simplest case the second voltage threshold switch consists of the series connection of a Zener diode and a current measuring resistor, the zener diode having a zener voltage has, which corresponds to the second voltage threshold. The tension increases on the secondary winding starting at zero, so is the second voltage threshold switch initially ineffective. When the second voltage threshold is reached the zener diode begins to conduct and closes the secondary winding as required from low resistance. The value of the second voltage threshold must be lower be as a threshold voltage which is the voltage controlled semiconductor switch required at least as control. When dimensioning the current measuring resistor there are two conditions to be met. On the one hand, the value of the Current measurement resistance to be small enough for a low-resistance termination of the Secondary winding is guaranteed. On the other hand, the value of the current measuring resistor be large enough so that the voltage on the secondary winding continues up can rise to the first voltage threshold.

Since in the current measuring resistor according to the invention the load current essentially proportional current flows, the voltage across the current measuring resistor is natural 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 an error. she is supplied to a shutdown device. To suppress interference, in the switch-off device the time average of the voltage across the current measuring resistor educated. If this exceeds a given limit value, the shutdown device stops another oscillation of the half-bridge inverter. this happens in particular by suppressing the control 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 flows can. Relevant standards (e.g. IEC 1000-3-2) write maximum amplitudes for the harmonics of the mains current. To comply with these standards have control gear, so-called PFC circuits (Power Factor Correction). An inexpensive Realization of these PFC circuits are so-called pump circuits, as they e.g. B. in EP 253 224 (cultivation bar) or EP 1 028 606 (Rudolph) are. When combining a pump circuit with a self-oscillating one Half-bridge inverters according to the prior art, there are problems with the Generation of the necessary ignition voltage for the gas discharge lamps and by high Power loss when switching the half-bridge transistors. Especially with large ones Power for the gas discharge lamps, the problems mentioned occur. A Cause for that are u. a. Storage times that are typical for bipolar transistors and do not allow a precise determination of the switch-off time. The present invention enables the use of voltage controlled semiconductor switches such as MOSFETS that have no storage times and therefore the problems mentioned can be avoided. This means that the half-bridge inverter according to the invention in combination with a pump circuit also advantageous for one Load can be applied that consumes a power of over 100W.

Another effect that with the half-bridge inverter according to the invention Pump circuit occurs, is the strong modulation of the operating frequency by the Mains voltage, which shows the oscillation of the half-bridge inverter. Dependent said operating frequency is within the current value of the mains voltage a frequency band that has a bandwidth of over 10 kHz. In order to are the electromagnetic disturbances that an operating device according to the invention caused spread over a wide frequency band. So the energy is a disturbed Device hits, advantageously low. In addition, the effort for interference suppression of an operating device according to the invention can be kept low.

Another advantageous use of the current measuring resistor according to the invention is given in the start circuit of the self-oscillating half-bridge inverter. A start capacitor is usually used to start the half-bridge inverter to charge and a part when reaching a trigger voltage at the charging capacitor the charge stored in the charging capacitor via a trigger element on the control electrode to discharge a half-bridge capacitor. Doing the problem occur that the charge pulse generated in this way to the control electrode in question is short and too low and there is no sustained oscillation of the half-bridge inverter is triggered. According to the invention, part of the stored charge of the Charging capacitor via a diode to the current measuring resistor according to the invention fed. This enables the half-bridge inverter to start up safely to reach.

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

The invention is to be explained in more detail below with the aid of exemplary embodiments. Show it:

Figure 1

the basic circuit of the operating device according to the invention

Figure 2

an embodiment of a control circuit according to the invention

Figure 3

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

Figure 4

an embodiment of a shutdown device according to the invention

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

In Figure 1, the basic circuit of an operating device according to the invention is shown. The control gear can be connected to a mains voltage via the connection terminals J1, J2 be connected. The mains voltage is fed to a block FR. It contains well-known filter and rectifier devices. The Filter devices have the task of suppressing interference. The rectifier device usually consists of a bridge rectifier consisting of four diodes. With the help of the rectifier device becomes a half-bridge inverter HB supplied a DC voltage. The half-bridge inverter contains essentially 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 an N-channel MOSFET. However, it is IGBT or P-channel MOSFET can also be used. In the N-channel MOSFET used in Figure 1, it is necessary that the positive Output of the rectifier device via a node 3 to the upper transistor T1 is supplied while the negative output of the rectifier device is connected to the ground potential M. The same polarity applies to standard ones IGBT. The polarity must be reversed when using P-channel MOSFET.

A storage capacitor C1 is located between node 3 and ground potential M. switched, which stores energy from the mains voltage before it is connected to a Lamp Lp is released.

The half-bridge inverter contains to control the half-bridge transistors T1, T2 HB a drive circuit 1, 2 for each half-bridge transistor T1, T2. The control circuits 1, 2 are each connected via a connection A to the respective one Gate connection and via a connection B to the respective source connection of the relevant half-bridge transistor connected. The control circuit 2 for the lower half-bridge transistor T2 has a third terminal S, on which a shutdown 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 connection of the load circuit is in Figure 1 connected to the ground potential M. The second connection can have the same effect of the load circuit can alternatively be connected to node 3. The load circuit consists essentially of the series connection of a primary winding L2 one Current transformer, a lamp inductor L1, a resonance capacitor C2 and a coupling capacitor C3. Parallel to the resonance capacitor C2 are over the Lamp terminals J3, J4 one or more lamps Lp connected in series can be connected. In the exemplary embodiment, the lamp filaments are not preheated intended. However, generally known devices are available to the person skilled in the art Spiral heating available, which he with the control gear according to the invention can use. It is also possible to connect several load circuits connected in parallel operate. The function of the individual elements of the load circuit can be the state of the Technology.

FIG. 2 shows a preferred exemplary embodiment of a control circuit according to the invention shown. A secondary winding L3 of the current transformer is between a node 20 and the connection B known from FIG. 1. A Diode D1 lies with its anode at node 20 and with its cathode at a node 21. Via a resistor R3, the node 21 is connected to that known from FIG Port A connected. An integrator is parallel to the secondary winding L3 switched that as a series connection of a timing resistor R1 and a timing capacitor C4 is executed and has an integration constant that the product from the values of R1 and C4. The junction of R1 and C4 forms a node 22. In parallel to C4, an integration value is tapped and the Control electrode of a semiconductor switch T3 supplied. The switching path of the semiconductor switch T3 lies between the connections A and B. This can be done in parallel, like In the exemplary embodiment, a resistor R4 is connected to increase the switching reliability become. The semiconductor switch T3 is preferred as a small-signal bipolar transistor executed.

Between node 21 and node 22 there is a first voltage threshold switch switched a first voltage threshold. It is designed as a Zener diode D3. exceeds the voltage fed into the drive circuit by L3 has a value, which leads to the Zener voltage of D3 being exceeded, so becomes the time capacitor C4 not only loaded via the time resistor R1, but also via D3, whereby the integration constant of the integration element is reduced.

According to the invention, there is a second one between the node 21 and the connection B. Voltage threshold switch switched with a second voltage threshold. He is preferred as a series connection of a Zener diode D2 and a current measuring resistor R2 executed. When the voltage at L3 rises, the over Port A controlled the assigned half-bridge transistor. After another According to the invention, the voltage across R2 rises to become the Zener voltage of D2 exceeded. This results in a current flow through the current measuring resistor R2, which is essentially proportional to the load current in the load circuit. So that will Prevents saturation of the current transformer and load current proportional Charge of the integrator reached. Is the current in the load circuit so great that the Zener voltage of D3 is exceeded, so there is a quick shutdown of the associated half-bridge transistor.

At the junction between D2 and the current measuring resistor R2 is a Port S led out. With regard to connection B, a load current can be connected to it proportional voltage can be taken. This can be done as shown below Shutdown device are supplied. Because the voltages in the shutdown device generally refer to the ground potential M, has only that drive circuit assigned to the lower half-bridge transistor has a connection S.

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

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

The lamp clamp J3 is connected to the first diode connection point via a pump capacitor C6 connected. The lamp clamp J3 stands out from the Lamp clamp J4 characterized by the value of the amplitude of its AC component is greater than the ground potential. The resonance capacitor C2 from Figure 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 over the series connection of a pump inductor L4 and a capacitor C7 with the second Diode connection point connected. Pump choke L4 can also be used directly at the node 4 known from FIG. 1, which is the connection point of the half-break transistors T1 and T2 are connected. The capacitor C7 essentially serves to block a direct current component in the current through the pump throttle L4.

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

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

Another variation possibility concerns the diodes D5 and D7. These diodes can also perform functions that the rectifier device in the block FR assigned. Corresponding diodes in the rectifier device can then omitted.

FIG. 4 shows how the current measuring resistor R2 according to the invention and thus Connected connection S from Figure 2 advantageous for a shutdown and a starting device of the control gear can be used.

The shutdown device contains a well-known thyristomach formation from the resistors R42, R43, R44 and R45 and the transistors T41 and T42. The thyristor simulation is via a resistor R41 with node 3 connected from Figure 1. The other end of the thyristor simulation is at ground potential M.

Via the connection S is a voltage divider consisting of the resistors R46 and R47 are fed a voltage that is proportional to the load current. The Voltage divider divides the voltage fed in to a value that is normally the control gear is not switched off. By a capacitor C40, the is fed by the voltage divider, the time average of the load current is formed and provided in the form of a voltage related to the ground potential. This Voltage is supplied to the control electrode of a semiconductor switch, which acts as a bipolar transistor T43 is executed. Exceeds the average of the load current in the event of a fault a predefined dimension, the thyristor simulation is made via the collector connection of T43 triggered. As a result, a connection G2 is connected via a diode D42 is connected to the control electrode of the lower half-bridge transistor, with the Ground potential M connected. This will result in further oscillation of the half-bridge inverter prevented.

The oscillation of the half-bridge inverter is started with the help of a generally known starting capacitor C41, which is made via the resistor R41 Mains voltage is charged. A trigger diode D40 (DIAC) is connected to C41. If the voltage at C41 reaches the trigger voltage of the trigger diode D40, the Control electrode of the lower half-bridge transistor via a diode D41 and A start pulse is applied to connection G2. In practice it happens that this start pulse is too short and the oscillation of the Half-bridge inverter takes place. Port S is therefore advantageously used: According to the invention, the connection S is connected to the trigger diode via a diode D43 D40 connected. The start pulse not only runs via diode D41, but also according to the invention also via the diode D43 and further via the diode D2 and the Resistor R3 from FIG. 2. The starting pulse is lengthened and enlarged which leads to a safe start of the oscillation of the half-bridge inverter.

Claims (8)

Control gear for operating gas discharge lamps with the following features: Self-oscillating half-bridge inverter (HB), which contains the series connection of two half-bridge transistors (T1, T2), Load circuit which is connected to the junction of the half-bridge transistors (4) and which contains a primary winding (L2) of a current transformer through which a load current flows which is taken from the half-bridge inverter (HB), one control circuit (1, 2) for each half-bridge transistor (T1, T2), each containing the following components: a secondary winding (L3) of the current transformer, an integration element (R1, C4) which essentially integrates the voltage on the secondary winding (L3) of the current transformer and switches off the relevant half-bridge transistor when a predetermined integration value is reached, a first voltage threshold switch (D3), which reduces the integration constant of the integration element when a given first voltage threshold is reached, characterized in that the half-bridge transistors (T1, T2) are essentially voltage-controlled transistors and at least one control circuit (1, 2) has a second voltage threshold switch (D2, R2) with a second voltage threshold that is lower than the first voltage threshold, the second voltage threshold switch (D2, R2) being connected in parallel with the secondary winding (L3) comes. Operating device according to claim 1, characterized in that the second voltage threshold switch contains the series circuit comprising a zener diode (D2) and a current measuring resistor (R2). Operating device according to claim 2, characterized in that the voltage across the current measuring resistor (R2) is fed to a disconnection device which evaluates the time average or the instantaneous value of this voltage and prevents further oscillation of the half-bridge inverter (HB) when a given limit value is exceeded. Operating device according to claim 1, characterized in that the operating device has two line voltage terminals (J1, J2) which can be connected to a line voltage and a power factor correction of a line current flowing through the line voltage terminals (J1, J2) is achieved by a pump circuit. Operating device according to claim 4, characterized in that the pump circuit has the following features: part of the grid current flows via a first pump diode (D5), which forms a first diode series circuit with a first diode connection point with a second pump diode (D6), the diodes being polarized so that they allow current to flow from the grid 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, one lamp terminal (J3) being connected to the first diode connection point via a pump capacitor (C6). Operating device according to claim 5, characterized in that the pump capacitor (C6) is connected to that lamp terminal (J3) which, compared to a reference potential (M), has a voltage which is the greatest value for the voltage at the other lamp terminals (J4) has the AC component. Operating device according to claim 5, characterized by the following features A second diode series circuit of two diodes (D4, D7) is connected in parallel to the first diode series circuit, which creates a second diode connection point, the diodes (D4, D7) being polarized so that they allow current to flow from the grid to the half-bridge inverter (HB). the second diode connection point is connected to the connection point (4) of the half-bridge transistors (T1, T2) at least via a pump choke (L4). Operating device according to claim 2, characterized in that the operating device contains a starting capacitor (C41) which is connected to the current measuring resistor (R2) via the series connection of a trigger diode (D40) and a diode (D43).

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