EP2801238B1

EP2801238B1 - Power supply circuit for control circuit of led lighting and led lighting

Info

Publication number: EP2801238B1
Application number: EP12812571.3A
Authority: EP
Inventors: Yaping Liu; Middel TJACO; Xuewei Dai; Chunjun JIANG
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2012-01-05
Filing date: 2012-12-17
Publication date: 2016-03-09
Anticipated expiration: 2032-12-17
Also published as: CN103200726B; EP2801238A1; WO2013102549A1; CN103200726A

Description

Technical field of the Invention

The application relates to a power supply circuit, and particularly to a power supply circuit for reliably supplying power to control circuit of Light Emitting Diode (LED) lighting. The application further relates to an LED lighting including the power supply circuit.

Background Art of the Invention

As the technology of LED light source advances, control circuits on board are necessary for LED light sources capable of working safely in various situations. The control circuit may trigger protecting activity in case of detecting overvoltage, overcurrent or overheat of driving power of the LED light sources, such as cutting off power supply to the LED light sources, thereby protecting effectively the LED light sources. However, the power supply is a problem in such a case since when power supply is cut off, voltage of the control circuit per se drops, and then the protecting activity cannot be triggered any longer.
US 2009 19 51 63 A1 discloses A solid state lighting unit constituted of a control circuitry; a single string of light emitting diodes, the single string constituted of a plurality of sections each comprising a plurality of light emitting diodes; and a plurality of bypass paths each responsive to the control circuitry, each of the plurality of bypass paths arranged to provide bypass to a particular one of the plurality of sections, wherein the control circuitry is operative to identify an open circuit condition of a particular one of the plurality of sections, and activate the bypass path arranged to bypass the open circuit section, thereby providing light through sections not exhibiting an open circuit condition. JP 2010 27 80 39 A discloses a LED illumination protection circuit which can be constituted inexpensively by monitoring a voltage at a mid point where a plurality of LEDs are connected in series by two transistors, detecting variations in the mid-point voltage of the supply voltage larger than or equal to a prescribed preset voltage width, and determining abnormalities in the plurality of LEDS.
The present solution to the technical problem is to supply the voltage regulator from the output voltage of driver directly. As shown in Fig. 1A, power input from a driver is directly connected to a voltage regulator 101 in addition to being supplied to LED light sources, the voltage regulator 101 generating suitable voltage and supplying the voltage to a control circuit 102, the control circuit 102 being connected to the gate of Metal Oxidation Semiconductor (MOS) transistor Q1 for controlling it. The control circuit 102 turns off Q1 in case of detecting failure such as overcurrent, so as to disconnect the current path of the LED light sources to protect the LED light sources. This solution is low cost, but low efficiency for this voltage is too high.
Another solution is to employ an additional switch power supply to supply power to the control circuit. As shown in Fig. 1B, an additional switch power supply 103 separately supplies power to a control circuit 104, such that the control circuit 104 can still be supplied with power unceasingly when protecting activity is triggered. This solution is complex and high cost, and that the duty cycle will be too small and efficiency will not be high.

Summary of the Invention

The technical problem to be solved by the application is to provide a simple, efficient and low cost power supply circuit for reliably supplying power to control circuit of the LED lighting, so as to ensure unceasing operation of control circuit no matter protecting activity is triggered or not. According to one aspect of the application, a power supply for control circuit of LED lighting is provided, the LED lighting comprising a plurality of LED light sources connected in series and a control switch for controlling on and off of current path of the LED light sources. The power supply circuit is characterized in that it comprises a first PNP transistor whose collector is coupled to a power input of the control circuit, emitter is coupled to a first node between a first group of LED light sources and a second group of LED light sources upstream the control switch, and a base is coupled to a second node between the control switch and the second group of LED light sources, such that when the control switch controls the current path to close, the first PNP transistor is on and when the control switch controls the current path to open, the first PNP transistor is off; a second NPN transistor whose base is coupled to the emitter of the first PNP transistor, emitter is coupled to the power input of the control circuit, and collector is coupled to power input of the plurality of LED light sources.
According to another aspect of the invention, an LED lighting comprising the above power supply circuit is provided.
In LED lighting using the above power supply circuit, in normal working situation, the power of control circuit is supported from middle tap of serial LEDs, and power supply may be utilized efficiently and energy is saved greatly. When protecting activities happen, even if the switch in serial with main circuit is off, the voltage supply will not be cut off since the current loop will be switched to another loop automatically, control circuit can work unceasingly, and control status will not change.

Brief Description of the Drawings

To further illustrate the above and other advantages and features of the invention, embodiments of the invention will be described hereinafter in detail in conjunction with the Drawings. It shall be understood that those drawings describe only typical embodiments of the invention, and thus cannot be regarded as a limitation to the invention. In the Drawings:

Figs. 1A and 1B are schematic views showing known solutions for supplying power to a control circuit;
Fig. 2 is a schematic view describing simply an LED lighting 200 of the application;
Fig. 3 shows an embodiment of a power supply circuit for control circuit of LED lighting of the application;
Fig. 4 is another embodiment of a power supply circuit for control circuit of LED lighting of the application.

Detailed Description of the Specific Embodiments

Generally, the embodiments of the invention relate to a power supply circuit. More specifically, the embodiments of the invention relate to a power supply circuit for reliably supplying power to control circuit of the LED lighting, thereby allowing ensuring unceasing working of the control circuit no matter the protecting activity is triggered or not.
An LED lighting 200 according to the application is briefly described by referring to Fig. 2 first.
As can be seen from Fig. 2, the LED lighting 200 comprises: a power input from a driver; N LED light sources D1-Dn for lighting, N≥1; a control circuit 202 for controlling and protecting safe operation of LED light sources; a power supply circuit 201 of the control circuit 202, which is coupled to a power input of LED light sources (via node 1), to a node 2 (which is also called as "middle tap" of a plurality of LED light sources) located between first group of LED light sources D4-Dn and second group of LED light sources D3-D1 upstream the control switch, and to a node 4 located between the control switch and the second group of LED light sources D3-D1; a control switch for controlling on and off of current path of a plurality of LED light sources, which is indicated typically by MOS transistor Q here, its gate being coupled to the control circuit 202 (via node 5) and being controlled by the control circuit 202, source being connected to ground and drain being coupled to node 4.
The application takes the following fact into account: LED conducting current can be more than 700mA, forward voltage is about 3.5V, and it is stable. So we can get the power to be supplied to the control circuit from the middle tap of LEDs. It should be noted that the "coupled to" used here is to define a direct connection between two circuit objects or among more circuit objects without any insertion circuit, and an indirect connection between two circuit objects or among more circuit objects implemented through one or more insertion circuits. For example, two circuit objects connected to each other directly is called as being "coupled to" each other. Also, provided two circuit objects are connected with one or more insertion circuits therebetween, they are also called as being "coupled to".
When the control circuit 202 does not detect abnormality of power input, power supply to control circuit 202 from positive electrode of the LED light sources is controlled by the control switch. On the contrary, when the control circuit 202 detects abnormality of power input, power supply to the control circuit 202 is switched by the control switch from middle tap of the LED light sources to power input of the plurality of LEDs.
Although the control switch is described typically as MOS transistor above, a person skilled in the art shall appreciate easily from the above that the control switch may comprise other active switch (like NPN transistor) or passive switch capable of implementing similar function.
Fig. 3 shows an embodiment of the power supply circuit 202 in the LED lighting 200 in Fig. 2. In Fig. 3, the control switch is still represented by MOS transistor Q3, and has a connection manner similar to that in the preceding description. The power supply circuit 201 comprises: a first PNP transistor Q2 whose collector is coupled to a power input of the control circuit 202, emitter is coupled to a node 2 between a first group of LED light sources D4-Dn and a second group of LED light sources D3-D1 upstream the control switch Q3, and base is coupled to a node 4 between the control switch and the second group of LED light sources D3-D1; a second NPN transistor Q1 whose base is coupled to emitter of the first PNP transistor Q2, emitter is coupled to power input of the control circuit 202, and collector is coupled to power input of the plurality of LED light sources D1-Dn.
In one embodiment variant, the power supply circuit 201 further comprises a resistor R1 coupled between collector of the second NPN transistor Q1 and power input of the plurality of LED light sources D1-Dn, a resistor R2 coupled between base of the second NPN transistor Q1 and emitter of the first PNP transistor, and a resistor R3 coupled between base of the first PNP transistor Q2 and node 4, although it is not required the same in all embodiments. Resistors R1, R2 and R3 provide suitable working points for transistors Q1 and Q2. Values of those resistors are selected in such a manner that when the control circuit 201 does not detect abnormality, transistor Q2 is turned on stably and transistor Q1 is turned off stably; and when the control circuit 201 detects abnormality, the transistor Q2 is stably turned off and the transistor Q1 is stably turned on, detailed introduction to this is provided as follows.
When power input of LED light sources is normal, the control circuit 202 sets base of control switch Q3 as high level to turn on Q3, current flows through LED light sources D1-Dn to make the LED light sources D1-Dn to light, meanwhile, voltage difference between emitter and base of the first PNP transistor Q2 is sufficient to exceed PN junction voltage between the emitter and the base to turn on the Q2, the turning on of the Q2 further allows power supply to the control circuit 202 from node 2 via emitter and collector of the first PNP transistor Q2. At this time, since voltage difference between base and emitter of the second NPN emitter Q1 is lower than PN junction voltage, Q1 is turned off, current will not flow to control circuit 202 via Q1, thereby prohibiting power supply to control circuit 202 from power input of the LED light sources via emitter and collector of Q1, wherein there is no power consumption on R1.
On the contrary, when control circuit 202 detects power input abnormality, the control circuit 202 sets base of control switch Q3 as low level to turn off Q3, current cannot flow through LED light sources D1-Dn to terminate lighting of the LED light sources D1-Dn to protect the LED light sources Dl-Dn, meanwhile, voltage difference between emitter and base of the first PNP transistor Q2 is smaller than PN junction voltage between the emitter and the base to turn off the Q2, the turning off of the Q2 further prohibits power supply to the control circuit 202 from node 2 via emitter and collector of the first PNP transistor Q2. At this time, since voltage difference between base and emitter of the second NPN emitter Q1 exceeds PN junction voltage, Q1 is turned on, current flow to control circuit 202 via Q1, thereby allowing power supply to control circuit 202 from power input of the LED light sources D1-Dn via emitter and collector of Q1. By such way, when failure is detected, power supply to control circuit 202 is switched from node 2 to power input of the LED light sources D1-Dn.
Fig. 4 shows another embodiment of power supply circuit 201 in LED lighting 200 shown in Fig. 2. In Fig. 4, first PNP transistor Q2, second NPN transistor Q1 and resistors R2 and R3 in power supply circuit 301 correspond to first PNP transistor Q2, second NPN transistor Q1 and resistor R2 and R3 in the preceding embodiment, respectively, so repetitive descriptions are omitted here. The power supply circuit 301 differs from the preceding embodiment in further comprising a resistor R4 coupled between node 2 and emitter of first PNP transistor Q2, and a resistor R5 coupled between emitter of second NPN transistor Q1 and power input of the control circuit 302.
Values of resistors R4 and R5 are selected in such a manner that when control circuit 302 does not detect abnormality and whereby Q2 is turned on, the resistor R4 provides suitable current feedback, when control circuit 302 detects abnormality and whereby Q1 is turned on, R5 provides suitable current feedback. Due to prohibition function of feedback on the system parameter fluctuation, the whole system is influenced less by the voltage fluctuation especially by short circuit of a single LED.
The above paragraphs explain preferred embodiments of a power supply circuit reliably supplying power to the control circuit. For example, node 2 between the first group of LED light sources and the second group of LED light sources may be set flexibly according to actual power requirement of the control circuit, for example, it may be located at positive electrode of D2. The power supply circuit may also not be limited to the PNP transistor and NPN transistor described above, and may be implemented by any device such as MOS transistor capable of implementing the above processes. MOS transistor Q3 may also be connected at other suitable position in current path of the plurality of LED light sources.
In such a manner, in normal working situation, the power of control circuit is supported from middle tap of serial LEDs, and power supply may be utilized effectively and energy is saved greatly. In addition, when protecting activities happen, control switch connected to the LED light sources in series turns off, no current flowing through LED light source, so LED light sources can be protected effectively; meanwhile, the voltage supply to the control circuit will not be cut off since the current loop will be switched automatically from middle tap of the LED light sources to power input of the LED light sources, control circuit can work unceasingly, and control status will not change.

Claims

A power supply circuit (201, 301) adapted to supply power to a control circuit (202, 302) of a LED lighting, wherein the LED lighting comprises:
- a plurality of LED light sources (D1, D2, ..., Dn) connected in series, wherein the plurality of LED light sources (D1, D2, ..., Dn) comprises a first group of LED light sources (D4 .. Dn) and a second group of LED light sources (D1 .. D3)

- a power input (1) of the plurality of LED light sources, wherein the first group of LED light sources (D4 .. Dn) is coupled between the power input (1) and the second group of LED light sources (D1 .. D3),

- the control circuit (202, 302),

- a control switch (Q3) adapted to be controlled by the control circuit (202, 302) so as to control on and off of a current path of the plurality of LED light sources (D1, D2, ..., Dn), wherein the second group of LED light sources (D1 .. D3) is coupled between the first group of LED light sources (D4 .. Dn) and the control switch (Q3), the power supply circuit (201, 301) being characterized in that it comprises:

- a first PNP transistor (Q2) whose collector is coupled to a power input (3) of the control circuit, whose emitter is coupled to a first node (2) between the first group of LED light sources (D4 .. Dn) and the second group of LED light sources (D1 .. D3) and whose base is coupled to a second node (4) between the control switch (Q3) and the second group of LED light sources (D1 .. D3), such that when the control switch (Q3) controls the current path to close, the first PNP transistor (Q2) is switched on and when the control switch (Q3) controls the current path to open, the first PNP transistor (Q2) is switched off;

- a second NPN transistor (Q1) whose base is coupled to the emitter of the first PNP transistor (Q2), and whose emitter is coupled to the power input (3) of the control circuit, and whose collector is coupled to the power input (1) of the plurality of LED light sources (D1, D2, ..., Dn).
The power supply circuit (201, 301) according to claim 1, wherein the control switch (Q3) comprises a metal oxide semiconductor transistor, whose gate is coupled to the control circuit (202, 302), whose source is coupled to ground and whose drain is coupled to the second node (4).
The power supply circuit according to claim 1 or 2, further comprising a first resistor (R1) coupled between the collector of the second NPN transistor (Q1) and the power input of the plurality of LED light sources.
The power supply circuit according to claim 3, further comprising a second resistor (R2) coupled between the base of the second NPN transistor (Q1) and the emitter of the first PNP transistor (Q2).
The power supply circuit according to claim 4, further comprising a third resistor (R3) coupled between the base of the first PNP transistor (Q2) and the second node (4).
The power supply circuit according to claim 1 or 2, further comprising a fourth resistor (R4) coupled between the first node (2) and the emitter of the first PNP transistor (Q2).
The power supply circuit according to claim 6, further comprising a fifth resistor (R5) coupled between the emitter of the second NPN transistor (Q1) and the power input of the control circuit (3).
A LED lighting, comprising the power supply circuit (201, 301) cording to any of claims 1-7.