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Circuit and method for the operation of an LED string supplied with alternating voltage

Patent

EP2792213

Owner

OSRAM GmbH

Filing Date

December 07, 2012

Priority Date

December 13, 2011

Portfolio

Lighting - OSRAM

Intro

Have a look the claims of this patent. Let's us know if you agree that they are relevant to circuit arrangements for filaments in LED retrofit lamps. The patent is active in Germany, the UK, France, Italy, Austria and Switzerland. It has counterparts in China and Korea.

Claims

1. Circuit arrangement (A, B, C) for operating a chain (14) comprising at least one light-emitting diode (13, 13') on an AC voltage, in particular...
  1. Circuit arrangement (A, B, C) for operating a chain (14) comprising at least one light-emitting diode (13, 13') on an AC voltage, in particular mains voltage, comprising - a rectifier (3) with an input circuit (1, 2) connected upstream of the rectifier for drawing the AC voltage and an output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8'', 9, 42, 43) connected downstream of the rectifier, into which a rectified AC voltage is output, characterized in that the circuit arrangement (A, B, C) further comprises: - an energy store provided in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43), in particular storage capacitor (5; 45, 46), to which the LED chain (14) can be connected in a parallel circuit, and - a current controller (6, 6', 6"), which is a control element (6, 6', 6"), which is connected in series, in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43), with the parallel circuit formed from the storage capacitor (5; 45, 46) and the LED chain (14), wherein during operation, it interrupts the charging of the storage capacitor (5; 45, 46) each time a current in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43) has risen to a specific threshold current and enables charging again when the rectified AC voltage in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6'', 8'', 9, 42, 43) has then fallen to a specific threshold voltage, in particular 0 V.
  2. Circuit arrangement (A, B, C) according to Claim 1, wherein the LED chain (14) has a forward voltage, for which 0.5 Vcc < Ufges < 0.9 Vcc, in particular 0.6 Vcc < Ufges < 0.8 Vcc and in particular 0.65 Vcc < Ufges < 0.75 Vcc, holds true, wherein Vcc is the peak value of the drawn AC voltage, and Ufges is the rated voltage of the LED chain (14).
  3. Circuit arrangement (A, B, C) according to one of the preceding claims, wherein 1.5 Iled < Ipeak < 4 Iled, in particular 2 Iled < Ipeak < 3 Iled, where Iled = rated current of the individual LEDs (13, 13') and Ipeak = threshold current.
  4. Circuit arrangement (A, B, C) according to one of the preceding claims, wherein the current controller (6, 6', 6''), during charging of the storage capacitor (5; 45, 46), transfers from a low-resistance state to a high-resistance state when the threshold current is reached and, when the voltage in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43) has fallen to the threshold voltage, returns from the high-resistance state to the low-resistance state again.
  5. Circuit arrangement (A, B, C) according to Claim 4, wherein the control element (6, 6', 6'') contains two branches (7-10; 7, 8', 9, 10; 42, 43, 8'', 9', 44) which are in parallel with one another in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8'', 9, 42, 43), of which branches a first branch (7, 8; 7, 8', 42, 43, 8") is conducting in the low-resistance state and is off in the high-resistance state, and a second branch (9, 10; 9', 44) is off in the low-resistance state and is conducting in the high-resistance state.
  6. Circuit arrangement (A, B, C) according to Claim 5, wherein the first branch (7, 8; 7, 8'; 42, 43, 8") contains a first switch (7; 42, 43) in series with a low-resistance resistor (8; 8'; 8"), and the second branch (9, 10; 9', 44) contains a high-resistance resistor (9; 9') in series with a second switch (10; 44).  
  7. Circuit arrangement (A, B, C) according to one of Claims 4 to 6, wherein, in the high-resistance state of the control element (6, 6', 6"), a current of at most 10%, in particular at most 5% and particularly preferably at most 2%, of the rated current of the LED chain (14) flows in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43).
  8. Circuit arrangement (A, B, C) according to one of the preceding claims, wherein the storage capacitor (5; 45, 46), in particular an electrolytic capacitor, has a capacitance of between 100 µF and 1000 µF per ampere of the rated current of the LED chain (14).
  9. Circuit arrangement (B, C) according to one of the preceding claims, which contains a phase-gating control unit (32, 33) for dimming purposes and an RC element is inserted into the input circuit of said phase-gating control unit.
  10. Circuit arrangement (B, C) according to one of the preceding claims, wherein the current controller (6', 6'') contains an additional control loop used for the closed-loop control of the current flowing through the LED chain (14) (LED current) by detection of the averaged AC voltage in the input circuit (1, 2) of the rectifier (3). 
  11. Lighting apparatus (LB; LC) comprising a circuit arrangement (B, C) according to Claim 10 and an LED chain (14) connected to the circuit arrangement, wherein the current controller (6', 6'') contains an additional control loop which is used for closed-loop control of the current flowing through the LED chain (14) (LED current) by detection of the LED current.
  12. Lighting apparatus (LB; LC) according to Claim 11, comprising means which detect and filter the LED current, subject the mean value obtained by filtering to a setpoint/actual value comparison and, using the difference signal obtained by the comparison, adjust the level of the threshold current to the LED rated current.
  13. Lighting apparatus (LB; LC) according to Claim 11 or 12, comprising means for reducing the setpoint value depending on the operating temperature.
  14. Lighting apparatus (LA; LB; LC) comprising a circuit arrangement (A, B, C) according to one of Claims 1 to 10, wherein the circuit arrangement (A, B, C), together with the LED chain (14), is accommodated on a printed circuit board, in particular on one of the two sides of the printed circuit board.
  15. Method for operating a chain (14) comprising at least one light-emitting diode (13, 13') on an AC voltage, in particular mains voltage, comprising a circuit arrangement having: - a rectifier (3) with an input circuit (1, 2) connected upstream of the rectifier for drawing the AC voltage and an output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8'', 9, 42, 43) connected downstream of the rectifier, into which a rectified AC voltage is output, - an energy store provided in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43), in particular storage capacitor (5; 45, 46), to which the LED chain (14) can be connected in a parallel circuit, and - a current controller (6, 6', 6"), which is a control element (6, 6', 6"), which is connected in series, in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6", 8", 9, 42, 43) with the parallel circuit formed from the storage capacitor (5; 45, 46) and the LED chain (14), characterized by the following steps: - during operation, the charging of the storage capacitor (5; 45, 46) is interrupted each time the current in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6'', 8", 9, 42, 43) has risen to a specific threshold current and is enabled again when the voltage in the output circuit (5-12; 5, 6', 7, 8', 9-12; 45, 46, 6'', 8'', 9, 42, 43) has then fallen to a specific threshold voltage, in particular 0V, - during steady-state operation, current flows both through the energy store (5; 45, 46) and through the LED chain (14) during the charge phase, and - in the discharge phase, the charge of the energy store (5; 45, 46) is conducted into the LED chain (14). 
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Buggi
January 08, 2018

Easy Micro storage converter Circuit with an added storage capacitor that is charged within a predefined current range of the LEDs. and discharged within another cuurent range. As these converter topologies are cheap and easy to set up, the relevance in lighting applications is growing. GoodIP: Thank you for your review, Buggi.


Aidin
January 04, 2018

This invention is related to LED drivers. Traditional techniques to drive a LED circuit, either by converting supply voltage to LED’s forward voltage or use switched regulators. Disclosed are simplified LED driver circuits using a rectifier, energy storage capacitor and a current controller, so that luminaires are robust, efficient and able to operate on high voltages even in presence of power fluctuations. Such circuits are simple and easy to use. The invention may be implemented in LED drivers, LED circuits having multiple LEDs etc.


Patent101
December 03, 2017

Argh, I do not speak German! But the English claims seem to confirm Mickey's view. GoodIP: Hi Patent101, You may want to have a look at the U.S. patent application. It's not alive any longer but it is in English ;-)


Mickey
December 02, 2017

Looks like a clever and simple circuit arrangement for operating a chain of LED on AC voltage. Instead of using a converter, the invention relies on a rectifier, an energy store and a circuit controller.


Franz
November 27, 2017

Smart invention for low cost applications of LEDs directly coupled to mains voltage.


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