DE102009010675A1 - Electronic ballast and lighting device - Google Patents

Abstract

Electronic ballast for operating at least one lamp, preferably a gas discharge lamp, with a center tap (M) arranged between a first (T1) and a second switch (T2), which can be connected to a terminal for the lamp and to a measuring input (LSCS) for idle detection having IC (1), which is provided for the operation of the ballast, wherein the measuring input (LSCS, ME) is preferably coupled between a reference potential connected to the shunt (R1) and a switch (S2), and with a circuit for variation the signal present at the measuring input (LSCS, ME), the circuit being designed as a transmission circuit (A) for reaching predetermined signal levels at the measuring input (LSCS, ME), in that a signal for switching a switch (T2) during a switching on at the center tap ( M) applied and negligible or there is no voltage (zero crossing of the signal) is generated.

Description

The The present invention relates to an electronic ballast for operation at least one lamp, preferably a gas discharge lamp, with one disposed between a first and a second switch Center tap, which is connectable with a connection for the lamp, and with a measuring input for deadtime detection having IC, which is designed for the operation of the ballast, wherein the Measuring input in particular between one with the reference potential connected shunt and a switch is coupled, and with a Circuit for varying the signal present at the measuring input. Furthermore, the present invention relates to a lighting device with a corresponding electronic ballast.

Generic ballasts are equipped with ICs, the according to the manufacturer often functions such as an automatic Deadtime detection or saturation control for the Lamp Throttle bring with it. Also is often an additional Shutdown threshold for faults implemented in ECGs. The necessary measuring input is hereby designed to overflow the electricity one, preferably the second switch or a voltage drop across the Measured against reference potential coupled shunt. A problem can then arise when the height the ignition voltage over the Halbbrückenshunt is set or programmed. If high ignition voltages needed be, for. For example series-connected bulbs, the shunt is due to the high Electricity during the ignition phase correspondingly low in the resonant circuit. The lower the resistance is the higher is the set ignition voltage. However, if the resistance falls below a certain value, it works Deadtime detection via the measuring input no longer, because the triggering threshold for switching on the (eg, MOSFET) transistor or switch is no longer achieved. If, on the other hand, higher-impedance shunts are used, they are in the ignition phase too fast a shutdown due to reaching the shutdown level threshold.

Furthermore comes with dimmable devices as additional To add difficulty that in certain dimming areas in the shunt Feels Power is so low that the minimum value for the implemented shutdown threshold for preheated electricity equipment no longer be achieved. Just as in the first problem case, at which can lead to current peaks, is also in the latter case a protective shutdown activated.

at a known solution the problem, the electronic ballast has an additional Circuit for varying the signal present at the measuring input in Form of a limiting circuit. For this purpose, in the line branch to Shunt also coupled to a reference potential diode coupled. The temperature dependence the forward voltage of the diode in the order of, for example 2 mV / K can occur with small shunts and a concomitant high ignition voltage, however serious for the ignition voltage impact.

It is therefore an object of the present invention, the disadvantageous state to improve the technique.

The Task is solved by an electronic ballast according to claim 1 and by a lighting device according to claim 10th

The Circuit for varying the signal applied to the measuring input is according to the invention as a transmission circuit for reaching predetermined signal levels formed that a signal for switching a switch during a negligible voltage applied to the center tap and / or not there existing voltage is generated. A nonexistent tension also corresponds to a negligible Tension. Decisive is the correct time recognition of the Zero crossing of the signal at the center tap, where also slightly different from "zero" Signals are usable. A signal is not in any Line branch between shunt and measuring input from one to zero potential switched diode influenced. This diode is dispensed with. The voltage dropping at the shunt will not trigger the Threshold for uses deadtime detection. Rather, it is directly on the switched off at the center tap voltage applied. This is then negligible, when the switch to be switched can be switched soft. at a bus voltage of, for example, 400 volts and simultaneous switching of the "low Side "switch this is the case when the voltage at the center tap is between +10 and -10 Volt is. Particularly advantageous, the signal is generated in this case, if the voltage at the center tap between -2 and +2 volts, and more preferably between +1 and -1 Volt is. The center tap is at the time of generating the signal and switching at quasi zero potential or ideally Zero potential.

When Signal, which from the transmission circuit transferred to the fair entrance is usually a tension, but it can also be a voltage change or a combination of voltage and voltage change.

If a line branch between shunt and measuring input is present, the transmission circuit in a branch to the measuring input before record your own signal and amplify it. It then acts as an amplifier circuit. Particularly advantageous, however, is an embodiment in which the transmission circuit superimposes any signal present in the line branch with another signal from other switching branches of the ballast, so that the two signals add in terms of magnitude and regardless of whether they have positive or negative signs , This ensures that the necessary measurement levels at the entrance to or for dead time detection are achieved in each case.

Instead of an enlargement of the Shunts and the over here falling voltage and the subsequent limitation of the Measurement input signal is used to detect the dead time correct moment an additional negative or positive pulse generated at the control input of the IC. About this can the shunt in particular for generating larger ignition voltages in areas of z. B. stay more than 600 V small. The inventive electronic ballast is thus optimal for a single-lamp operation with ignition voltages between preferably 500 and 700 V or for a two-lamp series circuit with ignition voltages between 600 and 1200 V usable. Furthermore, the losses minimized during operation. The ignition voltage is temperature independent adjustable, as in the line branch between switch and measuring input no diode applied to zero potential is arranged.

For overlay of the signal present at the measuring input with an additional signal positive and / or negative voltage comprises the transmission circuit preferably one between shunt and switch on the one hand and the Measuring input on the other hand coupled resistance. In addition, it is to this line branch, preferably between the measuring input and the coupled resistor a parallel to a switch to the Half-bridge center coupled, single-acting blocking element available. Regarding the Shunts are thus the coupled resistor and the one-sided acting blocking element, preferably a diode, parallel to a Switch, which in a training as a transistor also a May have freewheeling diode.

Provided now the other, d. H. not parallel to, preferably, the diode existing switch turns off, flows over the coil of the electronic ballast continue to stream, for example, a likewise existing Snubber capacitor is discharged. The half-bridge voltage drops due to the regular in the inductance energy and becomes negative. At the moment of zero crossing the voltage in the center tap flows through the freewheeling diode of the parallel switched switch a current. At the same time, the one-sided, parallel to the switch lying blocking device and it also flows a stream. This results in this connected to the measuring input Line branch a voltage drop, by the addition in the line branch coupled to the measuring input resistance amplifying influences becomes. At the same time, the signal originating at the half-bridge center becomes due to the sufficiently dimensioned resistance at the measuring input and not be forwarded to the shunt. Especially in combination with a resistance of significantly greater than the resistance of the shunt is, at the fair entrance one out the addition of the signals sufficient signal to reach the triggering threshold the deadtime detection. Thus, a simply constructed transmission circuit created triggered by the zero crossing of the center tap an additional Signal at the measuring input provides.

When one-way locking device is preferably a Schottky diode used.

Instead of the use of a sufficiently stress-resistant, one-sided acting Locking device may also use a transmission circuit instead on the one hand between one in the line branch to the measuring input arranged resistor and the measuring input itself coupled On the other hand, however, not necessarily at the half bridge center must be arranged. It is essential that when the half-bridge voltage drops to zero (or virtually zero) and thus at a time when the signal is to be generated at the switching input, this one corresponding Pulse at the measuring input triggers. Therefor can For example, from other of the already required switching elements or Circuits of an electronic ballast corresponding pulses or Signals are added or removed.

Especially advantageous in this case is the use of the usually anyway existing circuit for generating a floating supply voltage for one Switch, which is in particular to the bus voltage arranged switch acts.

Preferably includes the transmission circuit in such a design, a capacitor, which for generating a floating supply voltage required circuit with the line branch connects to the fair entrance. The circuit for the supply voltage points in this case usually at least one resistor, a diode and a capacity on, which are connected in series. Preferably the condenser on the side facing away from the measuring input between a diode and a resistor coupled.

in the Operation is the capacitor of the supply circuit in the turn-on phase the upper (high side) switch slightly discharged, the voltage across the Capacitor of the supply voltage minus the forward voltage of the Diode corresponds. The diode is locked in this phase, the voltage in the coupling point between transmission circuit and supply voltage circuit is constant and equal to the supply voltage for the Half-bridge circuit (VCC). Once the voltage at the bridge center negative or zero flows over the Diode and the resistance of the supply circuit a charging current to the associated Capacitor, the before for the operation of the high side switch energy needed again provides. The voltage at the coupling point to the transmission circuit breaks together and there is a negative impulse that persists for so long remains until the capacitor of the supply circuit is full again loaded. This negative pulse is transmitted through the capacitor of the transmission circuit forwarded to the fair entrance. At the entrance to the fair, the Switch-off threshold for deadtime detection reached.

Provided the transmission circuit Another resistance in the conduction path between shunt and measuring input has, they add the over dropping this resistance and transmitting the capacitor of the transmission circuit Voltages to the total signal applied to the measuring input. The duration This pulse at the measuring input is determined by the time constant resistance capacitor the transmission circuit determined, d. H. by variations of the resistance, the length of the Pulse can be varied.

Preferably can in the above-described embodiments also in the line branch to the switching input at least one filter in the form of a filter capacitor or an RC filter be to smooth the signal.

The The above-described object is further achieved by a lighting device, which with a ballast according to one of claims 1 is provided to 9. This lighting device come the above Benefits too.

Further Advantages and details of the invention can be found in the description take the following figures. Schematically shows:

1 a known standard solution for a half-bridge,

2 a circuit diagram of a ballast according to the invention,

3 a circuit diagram of another ballast according to the invention,

4 a circuit diagram of another ballast according to the invention,

5 a circuit diagram of another ballast according to the invention.

Equal or similar acting parts are - provided useful - with provided with identical reference numerals. Individual technical features The exemplary embodiments described below can also be used with the features of the above-described embodiments of the invention further developments to lead.

1 shows a known electronic ballast, which is for operating a lamp, not shown, which is preferably designed as a gas discharge lamp, is provided. The ballast comprises a first switch T1 and a second switch T2, between which a center tap M is arranged. About this the resonant circuit and the supply voltage for the lamp is operated or provided. The center tap M is thus indirectly connected to a terminal for a lamp, not shown. In addition, the electronic ballast has an IC 1 on, which is provided for the operation of the ballast and essential tasks of the control of the same takes over. A measuring input LSCS is coupled via a simple circuit A _VAR for varying the signal applied to the measuring input between the switch T2 of the half-bridge circuit and a shunt R1, which is connected to reference potential.

T1 is supplied via a bus voltage U _BUS , for example in the range of 400 V. Via connections VCC and HSVCC a floating supply voltage is realized. A HSGD port and a LSGD port represent the drivers for the gate of T1 and T2, respectively. A GND terminal is coupled to reference potential. The center tap M is connected to the HSGND pin of the IC 1 connected.

The Circuit for generating a floating supply voltage comprises Furthermore, a resistor R2, a diode D1 and a capacitor C1.

According to the embodiment according to 2 According to the invention, a transmission circuit A _{TZ is} coupled into the line branch leading from the shunt R1 or the transistor T2 to the measuring input. As described above, this transmission circuit A _TZ transmits an additional signal U _R2 at the moment of the zero crossing and thus the time of detection of the dead time to the measuring input, which imposes itself on the already existing there signal to a total signal U _CS .

On the other hand, the transmission circuit A _TZ is connected between D1 and R2 and, as described above, pushes a voltage pulse into the line branch to the LSCS via a capacitor C2. In sum, the voltage applied to the R1 and the C2 via C2 results in a sufficiently high voltage at the LSCS to reach the triggering threshold.

In 3 the transmission circuit is not coupled to the circuit for generating a floating supply voltage, but via a preferably designed as a Schottky diode diode at the same potential as the center tap M. If now turns off T1 flows due to stored in the not shown in detail and applied to M coil Energy continues to be electricity. The half-bridge voltage U _HB in M continues to decrease and becomes negative. At the moment of the zero crossing of the voltage in the center tap M, a current flows through the free-wheeling diode of the parallel-connected switch T2. At the same time, the unidirectional blocking device D _TZ , which is parallel to the switch T2, becomes conductive and a current also flows through the transmission circuit. This results in this connected to the measuring input line branch a voltage drop, which is additionally influenced by an additional drop in the voltage drop across the resistor R3. In particular, in combination with a resistance which is significantly greater than the resistance of the shunt, results at the measurement input LSCS from the addition of the voltages sufficiently large signal U _CS to reach the triggering threshold of the dead time detection. Preferably, R3 >> R1 with R3 / R1> 10 and particularly advantageous in a range R3 / R1 = 100. A capacitor C _F serves as a filter capacitor.

The transmission circuit is thus on the one hand as a gain of an already incurred at the LSCS signal. This amplification is accomplished by transmitting a signal tapped from other parts of the circuit. Instead of the simple components R3, Dom, or R3, C2 used, the transmission circuit can also be designed as a complex and then more elaborate converter, logic or inverter circuit and, for example, directly with a low-side pin LS of the IC 1 be connected. Advantageous in the circuits shown is therefore in particular the cost-effective production and the small footprint in the often cramped structures of an electronic ballast.

This simple structure also results from the embodiments of the 4 and 5 , These show the embodiments of the 2 and 3 Similar transmission circuits, however, do without a resistor R3 and transmit directly from the half-bridge center or the floating supply voltage of the electronic ballast, a signal to a measuring input ME. The basic function of the transmission circuits therefore corresponds to the now missing addition of the voltages, which in the examples according to 2 and 3 decrease over R3, the operation of the transmission circuits described in these figures.

Claims (10)

Electronic ballast for operating at least one lamp, preferably a gas discharge lamp, having a center tap (M) arranged between a first (T1) and a second switch (T2), which can be connected to a terminal for the lamp, and to a measuring input (LSCS ) for idle detection IC ( 1 ), which is provided for the operation of the ballast, wherein the measuring input (LSCS, ME) is preferably coupled between a shunt connected to the reference potential (R1) and a switch (S2), and with a circuit for varying the am at the measuring input (LSCS , ME) signal, characterized in that the circuit is designed as a transmission circuit (A _TZ ) for reaching predetermined signal level at the measuring input (LSCS, ME) that a signal for switching a switch (T2) during a at the center tap (M ) is applied and negligible or there is no voltage (zero crossing of the signal) is generated. Electronic ballast according to claim 1, characterized in that the transmission circuit (A _TZ ) applied to the measuring input (LSCS, ME) signal applied by an additional signal. Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) for transmitting a signal, preferably in the form of an additional positive and / or negative voltage, from a not directly connected to the measuring input (LSCS, ME) area of electronic ballast is formed, this signal can preferably be superimposed on a signal applied to the measuring input (LSCS, ME) signal. Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) a between shunt and a switch (T2) on the one hand and the measuring input (LSCS, ME) on the other hand coupled resistance (R3) has. Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) has a preferably parallel to a switch (T2) to the half-bridge center (M) coupled, one-sided blocking element (D _TZ ). Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) is coupled into a line branch for generating a floating supply voltage of a switch (T1) and / or directly to a control pin of the IC (LS). Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) is designed to transmit a signal originating from the circuit for generating a floating supply voltage. Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) _comprises a capacitor (C2). Electronic ballast according to one of the preceding claims, characterized in that the transmission circuit (A _TZ ) has a to the measuring input (LSCS, ME) adjacent line branch coupled filter (C _F ). lighting device with a lamp designed in particular as a gas discharge lamp, comprising an electronic ballast according to the preamble of Claim 1, characterized in that the electronic ballast after a the previous claims is trained.