EP2420109A1

EP2420109A1 - Electronic ballast for operating at least one discharge lamp

Info

Publication number: EP2420109A1
Application number: EP10728160A
Authority: EP
Inventors: Wolfram Sowa; Maximilian Gerber; Arwed Storm
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2009-07-30
Filing date: 2010-06-21
Publication date: 2012-02-22
Also published as: US20120112653A1; DE102009035371A1; CN102422720A; JP2013500557A; WO2011012373A1; JP5538538B2; US8587210B2; KR20120052379A; CN102422720B; DE102009035371B4; AU2010278193A1

Abstract

The present invention relates to an electronic ballast (10) for operating at least one discharge lamp having an input having a first and a second input connection for coupling to a DC supply voltage, wherein the second input connection is connected to an external reference potential (M_ext); a load circuit (R_L) having an output having a first and a second output connection for connecting the at least one discharge lamp; a constant-current transformer (12) comprising a converter throttle (L1), a converter diode (D1) and a converter switch (S1), wherein the converter throttle (L1) is coupled serially between the first input connection (E1) and the load circuit (R_L); an activation circuit that is configured to activate the converter switch (S1) in operation with an HF signal; wherein a first capacity (C_hi) is defined by the regions of the electronic ballast (10) that are connected in operation to an HF voltage, whereby a first voltage (U_chi) is defined that drops in operation via the first capacity (C_hi) with respect to the external reference potential (Mext); and wherein a second capacity (C_lo) is defined by the regions of the electronic ballast (10) that are supplied in operation with respect to HF on an internal reference potential (M_int) by a DC voltage; wherein at least one component is coupled between the internal (M_int) and the external reference potential (M_ext) via which a second voltage (U_clo) that is counter-phased to the first voltage (U_chi) drops in operation.

Description

description

Electronic ballast for operating at least one discharge lamp

Technical area

The present invention relates to an electronic ballast for operating at least one discharge lamp having an input with a first and a second input terminal for coupling to a DC supply voltage, wherein the second input terminal is connected to an external reference potential, a load circuit having an output with a first and a second output terminal for connecting the at least one discharge lamp, a choke converter comprising a converter choke, a converter diode and a converter switch, the converter choke being serially coupled between the first input terminal and the load circuit, a drive circuit configured to convert the converter switch in To drive operation with an RF signal, wherein a first capacitance is defined by the areas of the electronic ballast, which are connected in operation with an RF voltage, whereby a first voltage is defined, which in operation on the e The second capacitance is defined by the areas of the electronic ballast which, during operation, are supplied with a DC voltage with respect to an internal reference potential. State of the art

In such electronic ballasts, voltages of a few 100 V with frequencies of approximately 30 kHz to 1 MHz are switched by means of the choke converters. In this case, choke converters are converters in which current is taken from the supply voltage or fed back there during each working cycle. Two important representatives are the Bück converter and the boost converter. Such converters have a converter choke, a converter diode and a converter switch, wherein the converter choke is coupled in series between the first input terminal and the load circuit. In the high-frequency high-voltage switching described above, both conducted and radiated electromagnetic disturbances arise, which must be below the limits of the relevant EMC regulations. A distinction is made between common-mode interference, so-called Y interference, on the one hand, in which the charge equalization via the power lines takes place in phase, and differential mode noise, so-called X interference, on the other hand, in which the charge equalization via the power lines out of phase.

Common-mode chokes are often used in the mains input for the reduction of conducted common-mode noise. In difficult cases, however, this measure is often insufficient. From EP 0 763 276 B1 a method for active compensation of common-mode noise is known for further improvement. Based on the teaching of this document, for example, an opposite to the high-frequency half-bridge voltage can be generated. Since both voltages have a capacitive effect on the coupling the resulting disturbances due to their opposite phase. In particular, in reactor converters, as used in electronic ballasts according to the invention, this principle is not yet successfully applied, since the generation of an anti-phase voltage is possible only with great effort. Especially with frequency components above 1 MHz, the compensation no longer works satisfactorily, since the currents involved are not arbitrarily phase-locked as a result of the capacitances involved.

Particularly problematic are the already mentioned common-mode common-mode noise in devices of protection class 2, which must comply with the limit values of the relevant EMC regulations without a metallic housing and without protective conductor connection. In devices with a metal housing, in contrast, to a certain extent, an internal charge balance over the metal housing is possible.

SUMMARY OF THE INVENTION The present invention is therefore based on the object of developing a generic electronic ballast in such a way that it is distinguished by as few common-mode noise as possible, in particular also in the case of implementation without a metallic housing. This object is achieved by an electronic ballast with the features of claim 1.

The present invention is based on the recognition that different capacities for the formation of Common mode noise is responsible: A first capacitance is defined by the areas of the electronic ballast that are connected to an RF voltage during operation. As a result, in operation over this first capacitance a first voltage drops which is related to the external reference potential. In addition, a second capacitance is defined by the areas of the electronic ballast which, in operation, are supplied with a DC voltage in terms of HF in terms of an internal reference potential. If now it is possible to change the internal reference potential of the device in phase opposition to the interference source, ie to change the voltage which drops above the first capacitance, this can reduce the common-mode noise, which can be fully compensated in the case of I-drop. According to the invention, therefore, at least one component is coupled between the internal and the external reference potential, over which a second voltage drops in operation, which is opposite in phase to the first voltage. In other words, as a result of the first capacitance without this additional component, an HF current flowing via the first capacitance to the external reference potential is produced. This results in the said disturbances. If now the circuit part, which has no interference with respect to the external reference potential without the additional component, that is, the circuit part which is characterized by the second capacitance, caused by the insertion of the additional device that an HF current flows to the external reference potential, which is in phase opposition to the RF current generated by the first capacitance, the said disturbances can be reduced or even eliminated. Only by inserting the additional component Therefore, the second capacity RF-moderately unfolds an effect. With the additional component so that a voltage swing is introduced in the circuit part, which would be without the additional component at a constant potential. In the present case, this latter effect is exploited by suitable design in order to reduce or even compensate for the disturbing effect due to the first capacity.

As a result of this measure, the quality of the radio interference suppression, in particular of devices of protection class 2, is significantly improved with little effort. Because of the greater distance to the limit values of the relevant EMC standards, also critical installation situations can be controlled. For electronic ballasts that were previously only usable in luminaires of protection class 1, the range of application can be extended to devices of protection class 2.

In an advantageous embodiment, the at least one component represents a compensation inductance. This enables a particularly cost-effective implementation of the invention.

Preferred is the compensation inductance selected to L _k = 0.9 to 1.1 * (Ll * C _h i / Ci _0), wherein the Kompensa ^¬ tionsinduktivität is particularly selected to be L = _k * Chi Ll / C _0, where Chi the first capacitance, Ci ₀ the second capacitance, L _{k represents} the compensation inductance and Ll the inductance of the converter inductor.

The compensation inductance is preferably 0.01 to 0.9 times the inductance of the converter choke. This results in a clear demarcation to the known prior art current-compensated chokes based on a completely different principle. In the case of current-compensated reactors, the two reactors must have the same inductance in order to avoid magnetization due to the alternating current of the mains.

Particularly preferably, a snubber is coupled parallel to the compensation inductance. This allows the compensation behavior at very high frequencies, for example, from 5 MHz, improve. The snubber preferably comprises the series connection of a capacitor and an ohmic resistor.

Particularly preferably, the compensation inductance is coupled to the converter choke. As a result, a magnetic coupling is achieved, whereby the electrical properties, in particular the frequency response, of the two inductances are adjusted. Particularly preferably, the compensation inductance is wound on the same core as the converter inductor.

Converter chokes often have an additional winding for detecting the demagnetization of the converter choke. This results in the possibility of a particularly preferred embodiment of the present invention: In this case, this additional winding represents the compensation inductance. As a result, no additional inductance has to be used, as a result of which the winding structure is considerably simplified. Inductors which have been developed for use in inductance-type inductance choke converters can be adopted without modification in order to realize the present invention. The implementation of the present invention can be implement by adapting the PCB. In particularly preferred embodiments, the electronic ballast has no metallic housing and / or no protective conductor connection. As already mentioned, the choke converter can represent a boost converter, wherein the converter diode is coupled in series between the converter choke and the load circuit, wherein the connection point between the converter choke and the converter diode is coupled to the internal reference potential via the converter switch.

Further preferred embodiments emerge from the subclaims.

Short description of the drawing (s)

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Show it:

1 shows a schematic representation of a study of an electronic ballast;

FIG. 2 shows a first exemplary embodiment of an electronic ballast according to the invention; FIG. 3 shows a second embodiment of an electronic ballast according to the invention; and

Fig. 4 shows a third embodiment of an electronic ballast according to the invention. Preferred embodiment of the invention

Fig. 1 shows a schematic representation of a study of the present invention using the example of an electronic ballast with a throttle converter. The electronic ballast 10 is fed on the input side from a DC voltage source El. In practice, the DC voltage source El may represent an AC voltage source followed by a rectifier. The throttle converter 12 includes a converter inductor Ll, a converter diode Dl and a converter switch Sl, which is driven by a drive circuit, not shown, as is known in the art from the prior art. After the converter choke a storage capacitor Cl is arranged, the load circuit R _{L is connected in} parallel. The negative terminal of the DC voltage source El is coupled to an external reference potential M _ext , while the switch Sl of the inductance converter 12, the capacitance Cl and the load circuit R _L are coupled to an internal reference potential M _int . In the present case, a compensation inductance L _{K is} connected in series with the converter inductor L ₁ . The voltages applied to the two inductances are exactly proportional to one another assuming ideal components. In the standard configuration of a Bück- or Boost converter Ll is coupled to the positive output of the voltage source El. Now, if the compensation inductor L _κ serially coupled to the converter choke Ll, so to win first nothing. Relative to the internal reference Potential M _{int of} the electronic ballast are applied to the converter inductor Ll and the compensation inductance L _κ voltages Ui and U _κ in phase. Their amplitudes have the ratio Ui / U _κ . It is obvious that the currents through the converter inductor L 1 and the compensation inductance L _K have the same amplitude and phase at all times. Thus, the time derivative of the current is the same in both cases. With reference to FIG. 2, in a ballast according to the invention, the compensation inductance L _K is now coupled between the external reference potential M _ext and the internal reference potential M _int . With respect to the external reference potential M _ext falls on the converter inductor Ll, a voltage U _ch i and the compensation inductance L _κ a voltage U _c i ₀ from. At a positive edge to the transducer choke Ll, for example, when turning off the converter switch Sl, there is a negative edge on the compensation inductance L _κ. Seen from the external reference potential M _ext , the stroke of the voltage across the converter inductor Ll therefore decreases.

For reasons of principle, the connection between the converter inductor Ll, the converter switch Sl and the converter diode Dl is always kept as short as possible. The coupling capacity to the environment is referred to herein as Chi and therefore relatively small. For coupling capacity Chi thus contribute to all areas of the electronic ballast, which are supplied during operation of the electronic ballast with an RF voltage. On the other hand, all components which are supplied with a DC voltage with respect to the internal reference potential M _int during operation of the electronic ballast HF contribute to a second coupling capacitance Ci ₀ . A complete compensation of the capacitive currents through the coupling capacitances Chi and Ci ₀ takes place when: d / dt U _chl (t) * C _hl = d / dt U _c i ₀ (t) * Ci ₀ .

This results in a complete compensation when the compensation inductance L _{K is} chosen to:

Since the capacitance Ci ₀ is much greater than Chi, only a small voltage swing ΔU _C hi is required for compensation. This can be easily produced with inductive components small design or by means of an additional winding on the converter inductor Ll.

In the embodiment shown in Fig. 3 embodiment of a ballast according to the invention, the coupling between the transducer and the inductor Ll compensation inductance L _κ by the connecting line between the two inductances Ll is home, L _κ indicated.

The embodiment shown in FIG. 3 moreover comprises a snubber S _n , which in turn comprises the series connection of a capacitor C _s and an ohmic resistance R _s and is coupled in parallel to the inductance L _K. This snubber S _n enables an improvement of the compensation at high frequency ranges, preferably from 5 MHz. In a preferred embodiment, the capacitance C _{s is} 1.5 nF, the ohmic resistance R _s is 6.8 Ω.

In the previous description, ideal components were assumed. In fact, the inductors Ll, L _κ but have different parasitic parallel capacitances, which prevent complete compensation at higher frequencies. Depending on the desired degree of compensation, therefore, additional simple measures may be necessary in order to effect a good interference suppression over the entire necessary frequency range. Common are, for example, capacitors, resistors or small ferrite beads, which are connected in parallel or in series with the inductors L 1, L _K , as well as the switch S 1 and the diode D 1.

In the embodiment illustrated in FIG. 4, the reference numbers introduced with reference to FIGS. 2 and 3 continue to apply insofar as they relate to the same or similar components. Only the differences are discussed. Here, the compensation inductance L _{κ is} realized by an auxiliary winding, which normally serves to detect the demagnetization of the converter inductor Ll. For this purpose, the auxiliary winding L _κ on the one hand to the internal M _int , on the other hand connected to the external reference potential M _ext . Although the compensation inductance L _{κ is} used _{according to the} invention, it can also serve to detect the demagnetization of the converter inductor L 1. For this purpose, the voltage U _ZCD dropping across the compensation inductance L _{κ is} coupled to the input ZCD of a corresponding control device.

Claims

claims

1. Electronic ballast (10) for operating at least one discharge lamp with

- An input having a first and a second input terminal for coupling to a DC supply voltage (El), wherein the second input terminal to an external reference potential (M _ext ) is connected;

- A load circuit (R _L ) having an output with a first and a second output terminal for connecting the at least one discharge lamp;

- A choke converter (12) having a converter choke

(Ll), a converter diode (Dl) and a converter switch (Sl), wherein the converter choke (Ll) is serially coupled between the first input terminal (El) and the load circuit (R _L );

- A drive circuit which is designed to drive the converter switch (Sl) in operation with an RF signal;

wherein a first capacitance (Chi) is defined by the portions of the electronic ballast (10) operatively connected to an RF voltage, thereby defining a first voltage (U _ch i) which, when in operation, is above the first capacitance ( ₁₃ ). Chi) decreases with respect to the external reference potential (M _ext ); and

wherein a second capacitance (Ci ₀ ) is defined by the areas of the electronic ballast (10), which are supplied in operation HF-moderately based on an internal reference potential (Min _t ) with a DC voltage;

characterized, that between the internal (M _int) and the external reference potential (Mext) at least one component is gekop ^¬ pelt, is dropped across the second voltage during operation (U _do), to the first voltage (U _ch i) and out of phase ,

2. Electronic ballast (10) according to claim 1, characterized in that

the at least one component represents a compensation inductance (L _k ).

3. Electronic ballast (10) according to claim 2, characterized in that

that the compensation inductance (L _k ) is chosen to

L _k = 0.9 to 1.1 * (Ll * C _hl / Ci ₀ ),

wherein the compensation inductance (L _k ) is particularly selected

where chi is the first capacity,

Ci _{0 is} the second capacity,

L _{k is} the compensation inductance, and

Ll represents the inductance of the converter choke.

4. Electronic ballast (10) according to one of claims 2 or 3,

characterized,

in that the compensation inductance (L _k ) represents 0.01 to 0.9 times the inductance of the converter inductor (L 1).

5. Electronic ballast (10) according to one of claims 2 to 4,

characterized,

in that a snubber (Sn) is coupled parallel to the compensation inductance (L _k ).

6. Electronic ballast (10) according to claim 5, characterized in that

that the snubber (Sn) comprises the series connection of a capacitor (Cs) and an ohmic resistor (R ₃ ).

7. An electronic ballast (10) according to any one of claims 2 to 6,

characterized,

in that the compensation inductance (L _k ) is coupled to the converter choke (L 1).

8. Electronic ballast (10) according to claim 7, characterized in that

in that the compensation inductance (L _k ) is wound on the same core as the converter inductor (L 1).

9. Electronic ballast (10) according to one of claims 7 or 8,

characterized,

the converter inductor (L 1) has an additional winding for detecting the demagnetization of the converter inductor (L 1), this additional winding representing the compensation inductance (L _k ).

10. Electronic ballast (10) according to one of the preceding claims,

characterized,

that the electronic ballast (10) has no metallic housing and / or no protective conductor connection.

11. Electronic ballast (10) according to one of the preceding claims,

characterized,

the choke converter is a boost converter (12), the converter diode (D1) being serially coupled between the converter choke (L1) and the load circuit (R _L ), the junction between the converter choke (L1) and the converter diode (D1) is coupled via the converter switch (Sl) to the internal reference potential (M _int ).