DE102014217688A1 - Operating device for bulbs - Google Patents

Abstract

Operating device for lighting means, in particular converter for at least one LED, comprising a flyback converter, which is supplied from a DC supply voltage (26), wherein parallel to the primary winding (23) of the flyback converter, a discharge circuit is provided which is formed and is arranged that the electrical energy of voltage spikes, which arise when opening a primary-side switch (25) of the flyback converter, is temporarily stored in the discharge circuit and then discharged to the DC supply voltage (26).

Description

The present invention relates to a control device for lighting means, in particular a converter for at least one LED, comprising a flyback converter, which is supplied from a DC supply voltage.

So-called flyback converters, which are also referred to as flyback converters or clocked flyback converters, are used, for example, in the field of PFCs for operating circuits for lighting devices. Likewise, however, they are also used alternatively or additionally as a converter stage, it being possible for a light path, in particular an LED track, to be supplied from the output thereof. The invention particularly relates to these types of applications.

Furthermore, the use of such flyback converter is also provided in heating circuits for gas discharge lamps. In the WO 2012/167293 A1 For example, a method for switching a clocked flyback converter circuit is explained, wherein the clocked flyback converter circuits shown there are used for connecting heating coils for gas discharge lamps. As described there, in connection with gas discharge lamps, for example, thermally operating heating circuits are known which use a flyback converter clocked with a controllable switch, which, as already explained above, is also referred to as a flyback converter.

Flyback converters are basically used to transfer electrical energy between an input and an output side of galvanically isolated DC voltages and allow an input voltage to efficiently convert with a low circuit complexity in a defined output voltage level, whereby such flyback converter in other applications for power or voltage supply find, for example, in primary switched mode power supplies small power or voltage transformers in electronic devices.

As already explained above, the use of a flyback converter for a heating circuit of a gas discharge lamp, for example in the WO 2012/167293 A1 shown. 1 now shows schematically this basic use of a flyback converter, this schematic representation essentially the in

3 of the WO 2012/167293 A1 corresponds shown schematic representation. In 1 is a rectifier circuit 2 which is connected, for example, to a mains voltage and rectifies it. The rectified voltage is then passed through a PFC circuit 3 smoothed, with the PFC circuit 3 to an inverter circuit 4 connected, which is the bus voltage of the PFC circuit 3 converted into a suitable AC output voltage, the operation of a lamp 5 suitable is. In addition, there is the flyback converter 1 provided to the one in the bulb 5 provided heating coil is connected. The flyback converter 1 is doing by the PFC circuit 3 generated bus voltage (DC voltage) fed accordingly.

In 2 is then shown schematically and simplified a circuit of a known flyback converter. A flyback converter consists essentially of a primary-side arrangement 21 and a secondary-side arrangement 22 , The primary-side arrangement 21 has a primary winding 23 on. The secondary-side arrangement 22 In contrast, has a secondary winding 24 on. That is, the galvanically decoupled energy transfer takes place for example by a transformer or transformer with a primary winding 23 and a secondary winding 24 ,

In addition, then still on the primary side is a controllable switch 25 , which is preferably designed in the form of a circuit breaker, provided to store depending on the switch state on the primary side electrical energy and to transmit this to the secondary side. At the controllable switch 25 it is, for example, a MOS-FET, which is driven clocked accordingly. It should be noted that the switch 25 is arranged in series or series with the primary winding, which is stored with each switching cycle in the primary winding of the transformer energy and transmitted to the secondary winding of the transformer.

In addition to the WO 2012/167293 A1 also show the US 5,703,441 and the EP 1 806 832 A1 corresponding flyback converters for use in different areas.

A problem with such flyback converters now arises, inter alia, by non-ideal transformers. With the use of bipolar transistors, circuit losses are created by the non-ideal transformers when the switch or transistor is turned on and off (due to the overlap of the current and the voltage in the transistor during the opening and closing phases), with most of the loss occurring during the opening phase of the transistor. These circuit losses now occur in particular when using bipolar transistors as switches.

In contrast, when using MOS-FETs, the circuit losses, especially when opening or switching off the MOS-FET significantly lower, which is why in flyback converters often find appropriate MOS-FETs application.

These results then but the problem that can result in the opening or switching off of the MOS-FETs voltage, as when opening the primary side connected in series with the primary winding transistor, the primary winding tries to continue the current, which ultimately leads to a very fast and high voltage rise across the switch or transistor leads. This voltage peak can be so pronounced that damage to the transistor is possible.

To remedy this problem and to avoid possible damage to the transistor is in the US 2013/0063039 A1 provided on the primary-side arrangement of the flyback converter, a discharge circuit, which is also referred to as a snubber circuit. Like this document for example in 2 can be removed, the discharge circuit in detail a diode D1, a capacitor C _SN and a resistor R _SN .

It is then provided that the discharge of the capacitor C _SN via the ohmic resistance R _SN . That is, when switching in 2 of the US 2013/0063039 A1 the stored energy in the capacitor is discharged through the resistor R _SN , whereby this energy is dissipated under thermal stress. This leads to corresponding losses in the circuit and, in addition, it is then also necessary for the resistor R _SN to be dimensioned correspondingly large, since otherwise the resistor R _SN would possibly become too hot during this process.

To the US 2013/0063039 A1 should also be noted then that this in principle the application of a flyback converter to power a LED track 40 on the secondary-side arrangement of the flyback converter shows.

The object of the present invention is now to develop a control gear for bulbs with a flyback converter, which avoids in the flyback converter, that the switch provided in the primary-side arrangement is damaged by voltage spikes and on the other hand possible no or only very little thermal loads or losses occur.

The object is achieved by a control device for lamps according to claim 1. Advantageous developments of the inventions are the subject of the dependent claims.

According to the invention, an operating device for lighting means, in particular converter for at least one LED, is provided, which has a flyback converter which is supplied starting from a DC supply voltage, wherein a discharge circuit (snubber circuit) is provided parallel to the primary winding of the flyback converter is that is designed and arranged such that the electrical energy of voltage spikes, which arise when opening a primary-side switch of the flyback converter, is temporarily stored in the discharge circuit and then discharged to the DC supply voltage.

The primary-side switch of the flyback converter can be designed as a MOS-FET.

Advantageously, the flyback converter is part of a PFC circuit. Alternatively, it could also be provided that the flyback converter is part of a converter circuit which provides a voltage at its output, starting from which the lighting means can be operated.

Furthermore, it can preferably be provided that the discharge circuit has a capacitor, preferably fed via a diode, which preferably has a value between 0.3 nF and 10 nF, more preferably between 0.7 nF and 5 nF.

In this case, an inductance connected in parallel with the capacitor can additionally be provided, which preferably has a value between 5 mH and 100 mH, the value of the inductance of the discharge circuit being greater, preferably by a factor between 2 and 10, than the value of the inductance of a primary winding the flyback converter may be in series with the primary side switch.

The inductance of the discharge circuit is preferably not magnetically coupled to a primary winding of the flyback converter in series with the primary-side switch.

Furthermore, the discharge circuit has no ohmic resistance. Overall, therefore, the present invention offers the advantage that the energy from the voltage peak when opening the transistor or switch, which is arranged on the primary-side arrangement of the flyback converter by capacitor is cached and then back to the supply voltage or bus Tension of the flyback Converter discharges, wherein the discharge of the capacitor is provided to the bus voltage that supplies the flyback converter, in a second phase, which follows the voltage spike and the charging of the capacitor. In this case, the discharge takes place via the damping inductance.

Opposite the US 2013/0063039 A1 is thus no longer provided in the discharge circuit or snubber circuit resistance, which would lead to a thermal load or a loss in the degradation of energy.

The invention will be explained in more detail with reference to embodiments and the accompanying drawings. Show it:

1 schematic representation of a known from the prior art use of a flyback converter;

2 simplified representation of a circuit of a known from the prior art flyback converter;

3 simplified schematic representation of a circuit according to the invention.

As previously explained, shows 1 one already from the WO 2012/167293 A1 known use of a flyback converter 1 , taking to the flyback converter 1 corresponding heating elements of the bulb 5 be connected. In addition, there is a rectifier circuit 2 , a PFC circuit 3 and an inverter circuit 4 intended.

In 2 is then the circuit of an already known flyback converter simplified and shown schematically, wherein the flyback converter is a primary-side arrangement 21 with a primary winding 23 and a MOS-FET 25 and a secondary-side arrangement 22 with a secondary winding 24 having.

In addition, on the primary-side arrangement 21 also a supply voltage or bus voltage 26 provided, which is a DC supply voltage. The secondary-side arrangement 22 then also shows a consumer 27 , which, as already explained above, may be, for example, LED strips or heating coils for gas discharge lamps.

At the in 2 As previously explained, the flyback converter shown has the problem that when opening in series with the primary winding 23 switched MOS-FETs 25 the primary winding 23 tries to drive the current further, which ultimately leads to a very fast and high voltage increase across the MOS-FET 25 leads, causing damage to the MOS-FETs 25 can be done.

To solve this problem is then in 3 a flyback converter shown on the primary-side arrangement 21 additionally has a discharge circuit. It is quite generally provided that this discharge circuit, the energy from the voltage peak when opening the MOS-FETs 25 cached and then back to the supply voltage or bus voltage 26 of the flyback converter discharges.

In detail, this discharge circuit in this case has a capacitor 31 , a diode 32 and an inductance 33 on, wherein when opening the MOS-FETs 25 the voltage peak across the diode 32 the capacitor 31 fed. After the voltage spike and the charging of the capacitor 31 Then takes place in a second phase, the discharge of the capacitor 31 towards the bus voltage 26 that powers the flyback converter.

This then takes place via the inductance damping the discharge 33 , which thus defines the time constant for unloading. Here, the time constant is the frequency of the clocking of the MOS-FETs 25 Voted.

In the present invention, therefore, a process of charging / discharging in the discharge circuit or the snubber circuit is provided, in which substantially almost no electrical energy is dissipated and accordingly no thermal loads or losses occur.

In detail, it is then provided that the discharge circuit is substantially parallel to the primary winding 23 and serially or in series with the MOS-FET 25 is arranged. As already explained before, the diode feeds 32 the capacitor 31 , being parallel to the capacitor 31 the inductance 33 is provided.

Regarding the values of the capacitor 31 and the inductance 33 is preferably provided that the capacitor 33 has a value between 0.3nF and 10nF, in particular between 0.7nF and 5nF and the inductance has a value between 5mH and 100mH, the value of the inductance 33 the discharge circuit greater, in particular by a factor between 2 and 10, than the value of the inductance of the primary winding 23 of the flyback converter is.

General is about the inductance 33 the discharge circuit to note that the sizing of this inductance 33 is designed such that at the most anticipated drive frequency of the MOS-FET 25 (the inductance 33 builds up a voltage that is a permissible voltage drop across the MOS-FET 25 does not exceed, the inductance 33 is significantly larger than the inductance of the primary winding 23 in order to continue an efficient transmission to the secondary winding 24 to ensure.

The capacitor 31 the discharge circuit is further chosen to be sufficiently large, the triggered by the charging process by the voltage peak when opening the MOS-FETs 25 not the voltage ripple on the capacitor 31 Voltage levels reaching the MOS-FET 25 could affect. It should also be noted that the capacitor 31 The increase in voltage is limited accordingly.

Furthermore, it should also be noted that the primary winding 23 the flyback converter, which is in series with the MOS-FET 25 is arranged, not with the inductance 33 the relief circuit is magnetically coupled.

As a typical drive frequency for the flyback converter are, for example, 50 kHz to 300 kHz, preferably called 80 kHz to 150 kHz.

When using the flyback converter in conjunction with a PFC circuit, the supply voltage or bus voltage is usually in a range of up to 320 volts. When used as a circuit for driving an LED track, the bus voltage is usually in a range slightly above, such as 400 volts.

Overall, it should be noted once again that the discharge circuit in the primary-side arrangement 21 the flyback converter advantageously has no ohmic resistance.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2012/167293 A1 [0003, 0005, 0006, 0030]
• WO 2012167293 A1 [0009]
• US 5703441 [0009]
• EP 1806832 A1 [0009]
• US 2013/0063039 A1 [0013, 0014, 0015, 0025]

Claims (9)

Operating device for lighting means, in particular converter for at least one LED, comprising a flyback converter which, starting from a DC supply voltage ( 26 ), wherein parallel to the primary winding ( 23 ) of the flyback converter, a relief circuit is provided, which is designed and arranged such that the electrical energy of voltage spikes which occur when opening a primary-side switch ( 25 ) of the flyback converter, is stored in the discharge circuit and then to the DC supply voltage ( 26 ) is unloaded. Operating device according to claim 1, in which the primary-side switch of the flyback converter as MOS-FET ( 25 ) is trained. Operating device according to one of claims 1 or 2, wherein the flyback converter is part of a PFC circuit. Operating device according to one of claims 1 or 2, wherein the flyback converter is part of a converter circuit which provides at its output a voltage, from which the lighting means are operable. Operating device according to one of the preceding claims, in which the unloading circuit has a preferably via at least one diode ( 32 ) fed capacitor ( 31 ), which preferably has a value between 0.3 nF and 10nF, more preferably between 0.7 nF and 5nF. Operating circuit according to claim 5, further comprising a parallel to the capacitor ( 31 ) switched inductance ( 33 ), which preferably has a value between 5mH and 100mH. Operating device according to claim 6, that value of the inductance ( 33 ) of the relief circuit is greater, preferably by a factor between 2 and 10, than the value of the inductance of a primary winding ( 23 ) of the flyback converter in series with the primary side switch ( 25 ). Operating device according to claim 6 or 7, that the inductance ( 33 ) of the discharge circuit with a primary winding ( 23 ) of the flyback converter in series with the primary side switch ( 25 ) is not magnetically coupled. Operating device according to one of the preceding claims, that the discharge circuit has no ohmic resistance.

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