EP2425679B1 - Driver circuit for an led - Google Patents

Description

The invention relates to a driver circuit for an LED according to the preamble of patent claim 1.

Technical area

Such driver circuits are used in lighting systems to achieve a colored or flat lighting of rooms, paths or escape routes. Usually, the bulbs are driven by operating devices and activated as needed. For such illumination, organic or inorganic light emitting diodes (LED) are used as the light source.

State of the art

For lighting, instead of gas discharge lamps and incandescent lamps, light-emitting diodes are also increasingly being used as the light source. The efficiency and luminous efficacy of light-emitting diodes is being increased more and more so that they are already being used in various general lighting applications. However, light emitting diodes are point sources of light and emit highly concentrated light.

However, today's LED lighting systems often have the disadvantage that the color output or the brightness can change as a result of aging or by replacement of individual LEDs or LED modules. In addition, the secondary optics has an impact on the thermal management, as the heat radiation is hindered. In addition, it may come due to aging and heat to a change in the phosphor of the LED.

A brightness change is often possible only with a complex control circuit, a simple connection to standard dimmers is not given, as it comes in conjunction with most dimmers to a flicker of light, or the dimmer does not work. A typical driver circuit for LED is in Fig. 1 shown, this circuit does not include a device that ensures compatibility with dimmers and dimming with most commercially available dimmers for incandescent lamps is not possible.

With such dimmers, for example, via a phase control dimming or phase section dimming classic bulbs such as incandescent lamps can be dimmed, so controlled in the brightness.

Presentation of the invention

It is the object of the invention to provide a luminous means and a method which enables a trouble-free and energy-saving operation by a light emitting diode with light-emitting diodes without the above-mentioned disadvantages or with a significant reduction of these disadvantages.

This object is achieved according to the invention for a generic device by the characterizing features of claim 1. Particularly advantageous embodiments of the invention are described in the subclaims.

The solution according to the invention for a device for operating LEDs (organic or inorganic light-emitting diodes) is based on the idea that a driver circuit for an LED has a connection for a mains voltage, a filter circuit and a rectifier, an inductance and at least one switch.

The inductor is magnetized when the switch is closed, and the inductor is demagnetized when the switch is open, and at least during the demagnetization phase, the current through the inductor feeds the LED. A capacitor is coupled to a first terminal at the node between the rectifier and the unidirectional decoupler, coupled to its second terminal to the LED current or transformer. Thus, via this capacitor, a direct or indirect feedback of the LED current, whereby a uniform and defined charge of the buffer element is made possible by this feedback.

In this way, it is possible to achieve a very consistent and uniform illumination (for example, to illuminate a surface) by a light source with LEDs.

Description of the preferred embodiments

• Fig. 1 zeigt den Stand der Technik
• Fig. 2 zeigt eine Ausgestaltung einer erfindungsgemäßen Vorrichtung Nachfolgend wird die Erfindung anhand eines Ausführungsbeispiels gemäß Fig. 2 mit einer Treiberschaltung für eine LED erklärt.

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

• Fig. 1 shows the state of the art
• Fig. 2 shows an embodiment of a device according to the invention The invention is based on an embodiment according to Fig. 2 explained with a driver circuit for an LED.

Shown is a driver circuit for an LED, comprising a connection for a mains voltage, a filter circuit L1, a rectifier GR, and a latching element C1, a potential-separated switching regulator circuit with at least one switch S1 and a transformer L2, at whose output at least one LED is connected, wherein a unidirectional Entkoppelglied D1 between the rectifier and the latching element C1 is included. The driver circuit has a monitoring circuit U1, which activates the switch S1. About the control and timing of the at least one switch S1, which is connected to the primary side L2p, the transformer L2 is alternately up and demagnetized.

A capacitor C3 is coupled with a first terminal to the node between rectifier GR and the unidirectional decoupler D1, and this capacitor C3 is coupled with its second terminal to the LED current ILED or the transformer L2. Thus, via the capacitor C3, a direct or indirect feedback of the LED current ILED, whereby a uniform and defined charge of the latch element C1 is made possible by this feedback. In combination with the unidirectional decoupling element D1 and the rectifier GR, a uniform current consumption is thus also made possible via the connection for the mains voltage, since the capacitor C3 is recharged by means of the high-frequency feedback. The capacitance of the capacitor C3 and the frequency with which the transhipment occurs determine the amount of transmitted energy.

Thus, the driver circuit according to the invention by the uniform current consumption form a load for the dimmer, which allow trouble-free operation, for example, without flicker, even when dimming.

When the voltage at the second terminal of the capacitor C3 has a low potential, the capacitor C3 is charged via the rectifier GR, while the unidirectional decoupling element D1 blocks a direct current flow from the rectifier GR into the latching element C1. When the voltage at the second terminal of the capacitor C3 has a high potential, the capacitor C3 discharges via the decoupling element D1 in the latching element C1, while now the rectifier GR blocks a direct current flow from the rectifier GR in the latching element C1. The continuous charge of the capacitor C3 may result from the high-frequency clocking of the switch S1 and the associated high-frequency voltage or current change in the output circuit, in particular at the transformer L2 and possibly also at the LED.

The coupling of the capacitor C3 to the LED current ILED can take place via a second transformer whose primary winding L3a is traversed by the LED current ILED and whose secondary winding L3b is coupled to the capacitor C3.

The coupling of the capacitor C3 to the transformer L2 can be done by an additional secondary winding on the transformer L2. This additional secondary winding is magnetically coupled to the other windings of the transformer L2.

The second terminal of the capacitor C3 is thus preferably connected to an inductor L3b connected in series with the capacitor C3, wherein the inductance L3b is passed either as a further secondary winding on the transformer L2 or as a secondary winding of a further transformer whose primary winding L3a is traversed by the LED current ILED. is trained.

The coupling of the capacitor C3 to the LED current ILED can also take place indirectly, for example via a second transformer whose primary winding L3a is connected in parallel with the LED or at least one LED and whose secondary winding L3b is coupled to the capacitor C3. An indirect coupling to the LED current ILED is for example a coupling to the transformer L2, since the transformer L2 feeds the LED via the smoothing circuit (D2, C2).

In principle, therefore, with the rectifier GR, the capacitor C3 and the decoupling element D1, a feedback circuit is provided which allows a uniform and defined charge of the latching element C1, this feedback circuit is connected to a coupling point in the driver circuit, which due to the timing of the switch S1 on has alternating voltage potential (Since the driver circuit is a high-frequency clocked switching regulator, not only the voltage across the switch S1 is a high-frequency changing voltage, but also the potentials across the affected passive components change due to this timing).

Such an attachment point can be, for example, the connection to an inductor L3b connected in series with the capacitor C3, the inductance L3b being conducted, for example, either as a further secondary winding on the transformer L2 or as a secondary winding of a further transformer whose primary winding L3a is traversed by the LED current ILED. can be trained.

Other coupling points would also be possible, for example at another point in the output circuit (i.e., secondary side of the transformer L2, such as above the LED).

However, the coupling of the capacitor C3 to the LED current ILED can also be effected indirectly in that the capacitor C3 is coupled on the primary side of the transformer L2, for example directly or via an additional inductance to the primary winding L2p of the transformer L2. As already mentioned, other coupling points are possible, for example at a different point in the output circuit (in particular on the secondary side of the transformer L2, for example via the LED).

The latching element C1 may be formed by a smoothing capacitor. The latching element C1 may alternatively be formed by a passive valley fill circuit.

The monitoring circuit U1 can be, for example, an integrated circuit (for example an ASIC, microcontroller or DSP).

As already mentioned, the monitoring circuit U1 can also activate the switch S1. In this case, the monitoring circuit U1, for example, on the one hand monitor the current through the switch S1 by means of a current detection Ip (for example, a power shunt) and additionally monitor the current amplitude of the supply voltage Vin. In addition, the control of the switch (S1) may be dependent on further monitoring, for example, by monitoring the demagnetization of the inductance L2, the detected voltage of the LED or the detected amplitude of the current through the LED ILED. Preferably, all feedbacks or monitors on the secondary side are electrically isolated, i. the feedback of the detected on the output side (secondary side) signals to the monitoring circuit U1 via a potential separation (for example by means of opto-coupler or transformer). Preferably, as already explained, the switch-off duration of the switch S1 depends on the detected amplitude of the current through the LED ILED.

The switch S1 can be turned on by the monitoring circuit U1 whenever a demagnetization of the transformer L2 is detected by the monitoring circuit U1. Switching on the switch S1 can also be controlled by the monitoring circuit U1 so that it always takes place only when the transformer L2 is de-magnetized. A demagnetization can be detected by means of the monitoring circuit U1, for example by means of a voltage monitoring via the transformer L2 (for example by means of an additional secondary winding) or via the switch S1.

The switch-on and / or switch-off duration of the switch S1, which is predetermined by the monitoring circuit U1, may be dependent on the detected amplitude of the current through the LED ILED, whereby a feedback of the signals detected on the output side (secondary side), in particular of the current through the LED ILED, via a potential separation. The monitoring circuit U1 are thus preferably supplied with the detected signals via a potential separation. Preferably, however, the switch-on and / or switch-off duration of the switch S1 does not decrease to zero or close to zero. In a simple variant, for example, a limitation of the current through the LED ILED can be done by limiting the duty cycle. The current detection Ip can also be done directly at the switch S1 (for example, in a so-called. SENSE FET, which contains an integrated monitoring of the current).

As already explained, the switch-off duration of the switch S1 may depend on the detected amplitude of the current through the LED ILED. Preferably, the feedback of the detection of the amplitude of the current by the LED ILED is carried out electrically isolated (i.e., the control loop for the dependence of the switch-off duration of the switch S1). The switch-off duration can, however, also be fixed, for example (ie fixed).

The switch-off duration of the switch S1 may, for example, also be directly or indirectly dependent on the degaussing current of the transformer L2.

The switch S1 can be switched on whenever a demagnetization of the inductance (L2) is detected.

However, a switch-on can always take place only when the inductance (L2) is de-magnetized, and a certain period of time can also be between the time of demagnetization and the restart.

The monitoring circuit U1 can detect, for example, the voltage across the buffer element C1 or at the (positive) output of the rectifier GR1 or else, if present, the voltage before the decoupling element or the voltage difference across the decoupling element (preferably by a respective voltage measurement before and after the decoupling element Decoupling) capture. In a simple variant, the voltage is measured by means of a voltage divider which picks up the voltage across the buffer element C1 or at the (positive) output of the rectifier GR1 and reduces it to a potential which can be evaluated by the monitoring circuit U1.

However, the monitoring circuit U1 can also be designed (for example in high-voltage technology) so that it can directly detect the voltage across the buffer element C1 or at the (positive) output of the rectifier GR1.

The monitoring circuit U1 may be constructed discretely, but it may also be designed as an integrated circuit as mentioned. When using an integrated circuit as a monitoring circuit U1 further functions such as the direct control of the switch S1 can be integrated with.

The transformer L2, when demagnetized, can feed a smoothing circuit formed by a rectifier D2 and a capacitor C2. In a simple variant, however, an LED as a smoothing element can also assume the function of the rectifier D2 and other or even completely omitted further smoothing elements. But it is also possible that the LED are connected to the secondary side L2s of the transformer L2 directly in antiparallel connection, the transformer L2 can generate, for example, by using a center tap on the secondary side L2s two opposing voltages that feed the secondary side in time sequentially. This results in a secondary-side current with alternating amplitude, which can serve as a supply for a primary winding L3a and thus also for feeding the feedback circuit. This would be an example of the case where the feedback circuit is fed directly by the LED current ILED.

It can also be provided a secondary-side converter circuit which provides or regulates the current through the LED. This further converter circuit may follow the smoothing circuit D2, C2 and have an additional switch which clocks an additional secondary-side choke (ie, a further inductance). The LED can be powered by the charge and discharge of this additional secondary-side throttle with energy.

The coupling point for the feedback circuit may also be linked to the additional secondary-side throttle. For example, the coupling of the capacitor C3 to the LED current ILED can take place via a second transformer in such a way that the additional secondary-side throttle simultaneously acts as a primary winding L3a and is coupled to the secondary winding L3b.

However, it may also be arranged in series with the additional secondary-side throttle a primary winding L3a, which is coupled to the secondary winding L3b and serves to feed the feedback circuit.

The transformer L2 is magnetized when the switch is closed, and the transformer L2 is demagnetized when the switch S1 is opened, and at least during the demagnetization phase, the current through the transformer L2 directly or indirectly feeds the LED.

It can therefore transmit the driver circuit by high-frequency clocking of the switch S1 energy via the transformer L2 to the LED. The switch S1 may be, for example, a field effect transistor, such as a MOSFET, or a bipolar transistor.

The secondary winding L2s magnetically coupled to the primary winding L2p is preferably connected to a smoothing circuit having a rectifier D2 and a capacitor C2 to which the LED can be connected. The rectifier (D2) on the secondary winding L2s of the transformer can be formed by a diode D2 or by a full-wave rectifier.

The inductance L2 can feed a smoothing circuit during its demagnetization, this smoothing circuit can be for example a capacitor C2 or an LC (capacitor inductance C2-LG3) or CLC (capacitor-inductance - capacitor C2-LG3-CG3) filter.

The secondary side with the smoothing circuit is preferably designed so that a constant current supply of the LED is made possible.

The unidirectional decoupling element D1 can be formed by a diode.

Optionally, an additional diode can be interposed between the node between rectifier GR and the unidirectional decoupling element D1, preferably a fast diode, wherein additionally a capacitor can be arranged above the outputs of the rectifier GR. It can also be arranged between the rectifier GR and the junction of unidirectional decoupling element D1 and capacitor C3 an inductance as a support throttle. The support throttle can buffer energy while a current flows from the rectifier GR into the driver circuit, and release it again during a demagnetization phase.

It is also possible according to the invention that the transformer L2 is controlled by more than one switch, there are basically quite different switching control topologies used, such as an isolated flow converter or an isolated half-bridge converter. In this case, the course of the demagnetization of the transformer L2 and L2 can be dependent on the arrangement of the switch.

Of course, the switching regulator can also be operated by utilizing a resonance peaking, for example with a series or parallel resonant circuit, in order to minimize the switching losses in the switching elements (eg in the switch S1).

It can thus be formed with a socket for use of the light source in a commercially available lamp base, comprising a driver circuit according to the invention for an LED.

At least part of the driver circuit may be integrated in the socket.

The driver circuit can be connected to a commercially available dimmer. The driver circuit may be designed such that the voltage that drops across the buffer element C1 can be controlled via the dimmer, and thus the brightness of the LED can be controlled. By the feedback circuit according to the invention, a uniform charge of the latch element C1 can be carried out, wherein the position of the dimmer, the amount of energy supplied can be specified. The longer the time phase in which the dimmer passes a line voltage, the higher the voltage across the latching element C1 may become due to the uniform charge by the feedback circuit. About this voltage (over the latch element C1) can be adjusted directly or indirectly, the brightness of the LED by the driver circuit. For example, in the case of a fixed operation of the switch S1 (that is to say with a defined frequency and duty cycle), the current through the LED ILED is directly dependent on the voltage across the intermediate storage element C1.

Claims (10)

1. Driver circuit for an LED, having a connection for a mains voltage, a filter circuit, a rectifier (GR) and a buffer storage element (C1),
   an isolated switching regulator circuit having at least one switch (S1) and a transformer (L2), to the output of which at least one LED is connected,
   a unidirectional decoupling element (D1) being included between the rectifier and the buffer storage element (C1),
   characterized in that one connection of a capacitor (C3) is coupled to the node between the rectifier (GR) and the unidirectional decoupling element (D1), and the other connection of this capacitor (C3) is coupled to the transformer (L2),
   the capacitor (C3) being coupled to the transformer (L2) by means of an additional secondary winding on the transformer (L2).
2. Driver circuit for an LED,
   having a connection for a mains voltage, a filter circuit, a rectifier (GR) and a buffer storage element (C1),
   an isolated switching regulator circuit having at least one switch (S1) and a transformer (L2), to the output of which at least one LED is connected,
   a unidirectional decoupling element (D1) being included between the rectifier and the buffer storage element (C1),
   characterized in that one connection of a capacitor (C3) is coupled to the node between the rectifier (GR) and the unidirectional decoupling element (D1), and the other connection of this capacitor (C3) is coupled to the LED current,
   the capacitor (C3) being coupled to the LED current via a second transformer, the primary winding (L3a) of which has the LED current flowing through it and the secondary winding (L3b) of which is coupled to the capacitor (C3).
3. Driver circuit for an LED according to either of Claims 1 and 2,
   characterized in that
   the buffer storage element (C1) is formed by a smoothing capacitor.
4. Driver circuit for an LED according to one of Claims 1 to 3,
   characterized in that
   the buffer storage element (C1) is formed by a passive valley fill circuit.
5. Driver circuit for an LED according to one of Claims 1 to 4,
   characterized in that
   the switch (S1) is switched on whenever demagnetization of the transformer (L2) is determined.
6. Driver circuit for an LED according to one of Claims 1 to 4,
   characterized in that
   switching-on is always carried out only when the transformer (L2) is demagnetized.
7. Driver circuit for an LED according to one of Claims 1 to 6,
   characterized in that
   the switched-on and/or switched-off duration of the switch (S1) depends on the recorded amplitude of the current through the LED.
8. Driver circuit for an LED according to one of Claims 1 to 7,
   characterized in that the transformer (L2) supplies a smoothing circuit (D2, C2) during its demagnetization.
9. Driver circuit for an LED according to one of Claims 1 to 8,
   characterized in that
   the unidirectional decoupling element (D1) is formed by a diode.
10. Luminous means having a cap for using the luminous means in a commercially available lamp cap, having a driver circuit for an LED according to one of the preceding claims.

Images