EP2005803B1 - Reduced power loss in electronic ballasts - Google Patents

Abstract

An electronic ballast is disclosed, in particular for operation of gas-discharge lamps, in which a further power semiconductor is provided in addition to the conventional power semiconductor, and provides the power required for steady-state operation. This avoids the high-power MOSFET transistors, whose power losses are high, also being used for steady-state operation.

Description

The present invention relates to an electronic ballast (ECG) having a first power semiconductor, in particular a MOS-FET whose power is dimensioned to a starting power.

State of the art

Electronic ballasts (ECGs) are used in particular for lamps that a low-frequency line voltage is first rectified and then converted by means of a high-frequency inverter into a high-frequency square-wave voltage. As a result, for example, the efficiency of the lamps is increased and achieved a longer life.

In particular, discharge lamps, such as fluorescent tubes or energy-saving lamps, must be operated to limit the current with ballasts. In this case, the ignition of the lamp must be done with a high voltage, for which the ECG must provide a high so-called starting power. Depending on the lamp type, this starting power can amount to several hundred volts to several kV. In static operation - ie after ignition of the gas discharge - the current can be reduced again, since a low voltage is sufficient for the operation of the discharge lamp.

For the provision of voltage in the ballast, a power semiconductor is responsible, whose Dimension must be adapted to the required starting power. Most powerful MOSFET transistors are used, however, which have a high power dissipation when the lamp goes into static operation.

The US 4,066,930 discloses a circuit arrangement for powering fluorescent lamps.

Presentation of the invention

Object of the present invention is therefore to provide an electronic ballast, the efficiency is improved over conventional solutions.

This object is achieved by an electronic ballast having a first power semiconductor, in particular a MOS-FET whose power is dimensioned for a starting power, wherein the electronic ballast comprises at least a second power semiconductor, which has a different power than the first power semiconductor.

As a result, both power semiconductors can be used in the start-up phase, ie when starting, which makes it possible to provide a very high starting power, while in static operation the first power semiconductor is deactivated and only the second power semiconductor provides the static power. This allows the use of smaller sized power semiconductors, resulting in significant power savings, which in turn improves the overall efficiency of the system.

In addition, the use of smaller sized power semiconductors eliminates the problem that the very high driving power required by the

Using only one power semiconductor would be necessary to negate the advantage of high switching frequencies, since they degrade the efficiency. Special, for very high frequencies well suited power semiconductor but are very expensive, which in turn has a negative effect on the manufacturing cost. In addition, smaller power semiconductors have the advantage that the size of the housing in which they are installed, can be smaller.

Particularly advantageous is an embodiment in which the power semiconductors are dimensioned differently. In particular, it is advantageous for the static operation to use a second power semiconductor whose power is significantly lower than the power of the first power semiconductor.

Assuming that only about 1/3 of the starting power is required in static operation, for example, the power of the second power semiconductor can only be 1/3 of the power of the first power semiconductor.

In a further preferred embodiment, a control unit is provided which controls the activation or deactivation of the power semiconductors. If the power semiconductors are also arranged parallel to one another, the drive can be that a switch, for example a breaker contact, is activated, which deactivates the first power semiconductor, so that only the second power semiconductor provides the power.

Further advantages and preferred embodiments are defined in the subclaims.

Brief description of the drawings

In the following the invention will be further clarified by means of drawings. However, the exemplary drawings should not be used to limit the present invention to the illustrated embodiments.

• Fig. 1: eine schematische Teilansicht eines Schaltplans eines EVG's aus dem Stand der Technik;
• Fig. 2a: eine schematische Teilansicht eines Schaltplans eines ersten Ausführungsbeispiels des erfindungsgemäßen EVG's in eine Anlaufphase;
• Fig. 2b: eine schematische Teilansicht eines Schaltplans in Figur 2a gezeigten Ausführungsbeispiels des erfindungsgemäßen EVG's in einem statischen Betrieb; und
• Fig. 3: eine schematische Teilansicht eines Schaltplans eines zweiten Ausführungsbeispiels des erfindungsgemäßen EVG's.

Show it:

• Fig. 1 : A schematic partial view of a circuit diagram of a ballast from the prior art;
• Fig. 2a : A schematic partial view of a circuit diagram of a first embodiment of the electronic ballast according to the invention in a start-up phase;
• Fig. 2b : a schematic partial view of a circuit diagram in FIG. 2a shown embodiment of the electronic ballast according to the invention in a static operation; and
• Fig. 3 : A schematic partial view of a circuit diagram of a second embodiment of the electronic ballast according to the invention.

Preferred embodiment of the invention

In the FIGS. 1 to 3 only the components of the electronic ballast that are relevant to the invention are shown. In this case, the same reference numerals designate identical or analogous components.

FIG. 1 shows a partial view of a circuit diagram of a conventional electronic ballast and shows as selected components of the electronic ballast, a driver 2 which outputs a square-wave control signal, a power semiconductor 4 adapted to output the power required for starting a lamp, not shown, a transformer 6 for controlling the voltage supplied to the lamp with an output 8, for example, can be connected to such a lamp.

The power semiconductor 4 used in the prior art must provide the voltage necessary for ignition of gas discharge lamps. Due to the high voltage requirement, powerful power semiconductors, such as powerful MOS-FETs, are required. Although such MOS-FETs can easily provide the required power for igniting a gas discharge lamp, but consume even in the static operation of the lamp - ie after the ignition process - a lot of energy, so that sets a high power dissipation. This in turn results in a lower efficiency of the electronic ballast. In addition, the MOS FETs used here are relatively large, so that a desired miniaturization of the electronic ballast component-related limits are set.

Therefore, it is proposed in the present invention to use two small power semiconductors, which together, which can provide high power for the ignition, in static operation, however, only one power semiconductor is used.

Such an electronic ballast according to the invention is disclosed in FIGS. 2a and 2 B shown. It shows FIG. 2a the circuit of the electronic ballast in the start state and FIG. 2b the circuit of the electronic ballast in static operation.

According to the invention, a first power semiconductor 4 and a second power semiconductor 4 'are used in the embodiment shown here, which are connected in parallel. Furthermore, a switching element 10 is provided, which is suitable for activating or deactivating the power semiconductor 4.

In FIG. 2a is the start-up phase of an electronic ballast shown, ie the state in which a high voltage must be available to ignite, for example, a gas discharge lamp. For this purpose, the switch 10 in a closed position, whereby both power semiconductors 4, 4 'are connected in parallel, so that complement their performance.

If the gas discharge lamp goes into static operation, the first power semiconductor 4 can be deactivated. This will, as in FIG. 2b shown, the switch 10 is opened, so that a power is delivered only via the second power semiconductor 4 '. Since the second power semiconductor 4 'alone has to provide only a smaller power, it can also be optimized for this smaller power. This significantly reduces the power loss of the electronic ballast.

Particularly advantageous is an embodiment in which the power of the second power semiconductor 4 'is additionally lower than the power of the first power semiconductor 4. This is possible because in static operation often only 1/3 of the power required for the starting process must be provided. This is in the FIGS. 2a , and 2 B characterized schematically in that the second power semiconductor 4 'is shown smaller is, as the first power semiconductor 4. This results in even more power savings.

In addition, only a small power semiconductor is to be addressed for switching operations, which consumes significantly less energy, which can improve the overall efficiency of the system.

In FIG. 3 is the partial view of a circuit diagram of a second embodiment of the inventive EVG's shown. This is different from the one in FIG. 2a and 2 B shown embodiment in that the switch 10 is integrated in the driver 2. This can be realized, for example, by a control unit 12, which either makes both lines 14 and 14 'accessible, so that the first and the second power semiconductors 4, 4' can provide power, or block the line 14, so that the power semiconductor 4 is deactivated is.

Disclosed is an electronic ballast, in particular for the operation of gas discharge lamps, in which to the conventionally existing power semiconductor, a further power semiconductor is present, which provides the necessary power for static operation.

Claims (8)

1. Electronic ballast having a first transistor (4), in particular a MOSFET, whose power is dimensioned with respect to a start-up power, the electronic ballast comprising at least one second transistor (4'), and the first and second transistors (4, 4') being arranged in a parallel manner, characterized in that the second transistor (4') has a power which is different from that of the first transistor (4).
2. Electronic ballast according to Claim 1, the second transistor (4') having a lower power than the first transistor (4).
3. Electronic ballast according to one of the preceding claims, provision also being made of a control unit (12) which drives the first and second transistors (4, 4').
4. Electronic ballast according to one of the preceding claims, the control unit (12) driving the first and second transistors (4, 4') in such a manner that the first and second transistors (4, 4') are connected in parallel in order to provide the start-up power, as a result of which the start-up power is provided by both transistors.
5. Electronic ballast according to one of the preceding claims, the ballast changing to steady-state operation with a steady-state power after the starting operation with the start-up power, and the power for steady-state operation being provided by the second transistor (4').
6. Electronic ballast according to Claim 5, the control unit (12) driving the first and/or second transistor (4, 4') in such a manner that the steady-state power is provided by the second transistor.
7. Electronic ballast according to one of the preceding claims, provision also being made of a switching element (10) which is designed to deactivate the first transistor (4).
8. Electronic ballast according to Claim 7, the switching element (10) being able to be driven using a control unit.

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