EP1894300A1

EP1894300A1 - Power supply system and method for the operation of an electrical load

Info

Publication number: EP1894300A1
Application number: EP06743161A
Authority: EP
Inventors: Peter Trattler
Original assignee: Austriamicrosystems AG
Current assignee: Ams Osram AG
Priority date: 2005-06-20
Filing date: 2006-06-14
Publication date: 2008-03-05
Anticipated expiration: 2026-06-14
Also published as: KR101159931B1; KR20100018074A; KR20080032090A; JP2008547368A; DE102005028403B4; US20090212717A1; DE202005021665U1; US8063585B2; KR100989021B1; WO2006136321A1; DE102005028403A1; EP1894300B1; JP4955672B2

Abstract

Disclosed is a power supply system comprising at least one branch that encompasses a power source (1) and means (2) for connecting an electrical load (3). A comparator (5) with a transistor (7) that is mounted downstream thereof is connected to a voltage tapping node (4) of said branch. The transistor (7) is connected to a joint signal line (8) which is connected to a feedback input of a direct voltage regulator (10). The inventive system can be expanded by any number of additional branches which share the same signal line (8). The disclosed power supply system is particularly suitable for supplying several LED lines used for illumination purposes and display units.

Description

description

Power source arrangement and method for operating an electrical load

The present invention relates to a power source arrangement, the use thereof, and a method for operating an electrical load.

Power source arrangements serve, for example, to supply one or more electrical loads with electrical energy. In this case, for example, a plurality of series circuits, each comprising a current source and an associated load, may be provided. If the branches connected in parallel are supplied with a common supply voltage, it may be desirable to regulate the supply voltage. In this case, for example, the voltage drop across each current sink voltage can be measured and then the minimum of the current sink voltages can be determined. This lowest current sink voltage is compared with a desired value and depending on the comparison result, the supply voltage is varied. This ensures that the minimum voltage drop across the current sink corresponds at least to the threshold value. As a result, all power sources work in a predetermined voltage range.

The object of the present invention is to provide a current source arrangement and a method for operating an electrical load, in which a simple Schaltungsauf- construction with good efficiency is possible. According to the invention the object is achieved with respect to the device by a current source arrangement having the features of patent claim 1.

With regard to the method, the object is achieved by a method having the features of patent claim 18.

Advantageous developments of the proposed principle are each the subject of the dependent claims.

The proposed power source arrangement includes a power source and associated means for connecting an electrical load. The current source and the means for connecting an electrical load are connected to one another such that a common current path is formed when the electrical load is connected. A voltage tap node is coupled to the means for connecting an electrical load. This is designed such that a voltage dropping across the electrical load and / or the current source or a signal derived therefrom can be tapped off. A comparator is connected at its first input to the tap node. A second input of the comparator is arranged to supply a reference threshold. An output of the comparator is connected to a control input of a transistor. The transistor has a controlled path, which is connected between a signal line and a reference potential connection. A DC voltage regulator, for example a DC / DC converter, is designed at an input for supplying an input voltage. An output of the DC regulator is connected to the means for connecting the electrical load. A feedback input of the DC regulator is connected to the signal line. If too low a voltage drops above the power source, the signal line is pulled down. Thus, the feedback input of the DC regulator is pulled down. As a result, the DC regulator compensates for this by increasing its output voltage to regain the correct feedback voltage at the feedback input.

Of course, instead of a branch comprising a current source and means for connecting an electrical load, a plurality of such branches may be provided. In this case, preferably each branch, comprising a means for connecting an electrical load and an associated current source, each associated with a comparator with downstream transistor. Common to all branches, however, is the signal line and the DC voltage regulator.

Preferably, at least one further current source and at least one further means for connecting an electrical load is provided, which is connected to the at least one further current source. At least one further voltage tapping node is coupled to the at least one further means for connecting an electrical load. At least one further comparator with a first input, which is connected to the at least one further tap node, and with a second input configured for supplying at least one further reference source is provided. At least one further transistor is connected to it, which is connected on the load side to the common signal line.

If a voltage that is too low drops across any one of the current sources, it pulls the common signal line down via the comparator and the transistor. Consequently Also, the feedback input of the DC regulator is pulled down, which is compensated by the DC voltage regulator by increasing the supply voltage at its output until the voltage at the feedback input again corresponds to the desired target value.

The proposed principle is characterized in particular by a high efficiency. The proposed circuit can be realized in a simple manner and in a small size. Furthermore, it is characterized by the fact that it can be easily extended, cascaded and configured almost arbitrarily. Any number of power sources can be added without the need for additional circuitry, even across different semiconductor chips. Between several power sources, only a single line is required, namely the designated here as a signal line line. If in each case a plurality of different load types are to be controlled, for example red, green and blue (RGB) light-emitting diodes, abbreviated LEDs, the current sources can preferably be arranged in groups such that a common signal line is provided for each load type.

The reference thresholds may be the same or different.

The electrical loads each comprise at least one light emitting diode or a series connection of a plurality of light emitting diodes.

Alternatively, the branches, each comprising a current source and a means for connecting an electrical load, may be grouped together such that there is a means between the tap nodes of such a group and the comparator is switched to select a minimum input voltage.

If different types of electrical loads to be controlled, it can be provided for each type of electrical loads depending on a common signal line. For example, the types of loads may be light emitting diodes of different colors, such as red, green and blue light emitting diodes.

The voltage tap node may be coupled to the means for connecting an electrical load such that the voltage tap node is formed at a control terminal of a current source transistor, wherein the controlled path of the current source transistor is formed in a common current path with the means for connecting the electrical load. This has the advantage over a voltage tapping between the current source and the electrical load, that a safer signal tapping is ensured in the event of production fluctuations of the transistor parameters.

The comparator may comprise an operational amplifier. The combination of comparator and downstream transistor is preferably designed so that at different input levels at the input of the comparator not a rapid tilting of the output level to an extreme value, but rather that at the output to the difference at the input proportional signal is provided. This means that preferably a finite amplification is provided. This gain can be expressed in amperes per volt (current output to voltage input). The DC voltage regulator preferably comprises a so-called DC / DC converter. This is preferably designed as a so-called inductive Bück converter or down converter, Boost Converter or boost converter, buck / boost converter, capacitive charge pump, LDO (linear regulator) or the like.

In order to stabilize the control circuit of the DC-DC converter, a low-pass filter is preferably provided.

Minimum and maximum limits for the output voltage of the DC-DC converter can be set exactly by resistor divider ratios. This can be achieved with advantage that even if an electrical load fails, the supply voltage at the output of the DC voltage converter always remains within the specified limits for this output voltage.

The proposed principle is preferably generally suitable for lighting applications. In particular, the proposed principle for the backlighting of liquid crystal displays, LCD, is suitable. Preferably, the proposed principle can be used in such lighting applications in which a plurality of LED series circuits or chains are provided.

The invention will be explained in more detail below with reference to several embodiments with reference to the drawings.

Show it:

1 shows an embodiment of a current source arrangement according to the proposed principle based on a circuit diagram, FIG. 2 shows a further exemplary embodiment of a current source arrangement according to the proposed principle on the basis of a circuit diagram,

3 shows an embodiment of an arrangement with DC voltage regulator according to the proposed principle,

FIG. 4 shows a further exemplary embodiment of a current source arrangement according to the proposed principle,

FIG. 5 shows another embodiment of a current source arrangement according to the proposed principle,

FIG. 6 shows an exemplary embodiment of a current source arrangement according to the proposed principle with different load types,

FIG. 7 shows a first exemplary embodiment of a comparator transistor arrangement,

FIG. 8 shows another embodiment of a comparator transistor arrangement,

9 shows a still further embodiment of a comparison transistor arrangement for use in a circuit according to one of the figures 1, 2, 4 to 6, and

10 shows an exemplary embodiment of a voltage tap formed on the control input of the current source transistor according to the proposed principle.

FIG. 1 shows a current source arrangement according to the proposed principle. A power source 1 is in a common Current path connected to a means 2 for connecting an electrical load 3. Between the power source 1 and the electrical load 3, a voltage tap node 4 is formed. The voltage tap node 4 is connected to an inverting input of a comparator 5. Another input of the comparator 5 is provided with reference numeral 6, non-inverting and designed to supply a reference threshold V _c . The output of the comparator 5 is connected to the control input of an associated transistor 7. Transistor 7 may be a MOSFET or bipolar transistor. The controlled path of the transistor 7 is connected between a common signal line 8 and a reference potential connection 9. The signal line 8 is connected to a feedback input of a DC voltage regulator 10 for its control. The DC voltage regulator 10 has a

Input 11 for supplying an input voltage and an output 12 for providing a supply voltage VDD as a function of the input voltage and the level of the common signal line 8. This output 12 of the DC voltage regulator 10 is connected to another terminal of the terminal 2 for connecting the electrical load 3rd connected.

By analogy with the current branch, comprising the electrical load 3 and the current source 1, further current branches, each comprising a further electrical load 13, 23, and a further current source 20, 21 are provided. In each case, a connection of the electrical loads 3, 13, 23 is connected to the output 12 of the DC voltage regulator. At each of these branches, comprising an electrical load 3, 13, 23 and a current source Ie, 20, 21, a comparator 5, 15, 25 with a downstream transistor 7, 17, 27 is connected across the respective voltage tapping node 4, 14, 24 connected. Each of these transistors 7, 17, 27 is connected to a load connection to the common signal nalleitung 8 connected, which leads a return voltage UV.

The signal UV of the common signal line controls the supply voltage VDD. If one of the current sources 1, 20, 21 has too low a voltage (a voltage below the comparison potential V _c ), the line 8 is pulled slightly downward with respect to the voltage UV. Thus, the voltage at the feedback input of the DC regulator 10 is pulled down. This is compensated by the DC voltage controller 10 in that the voltage VDD at the output 12 is increased. The voltage VDD at the output is increased until the correct voltage UV is present at the feedback input.

The DC voltage regulator 10 can be any adjustable DC / DC

Be a converter. This serves to control the loads 3, 13, 23 with high efficiency. For example, the voltage regulator 10 may be an inductive buck, boost, buck / boost regulator or a capacitive charge pump or a simple series regulator.

The circuit according to FIG. 1 has a simple circuit structure, which can be implemented in particular in integrated circuit technology with a small area requirement. The circuit can be easily extended, cascaded and configured with additional branches. Any number of power sources can be added, requiring no additional circuitry. An advantageous feature of the circuit of Figure 1 is that only one line, namely the common signal line 8, is required for coupling the individual power source branches together. FIG. 2 shows a further exemplary embodiment of a current source arrangement according to the proposed principle, which largely coincides with the circuit according to FIG. 1 in the components used and their advantageous interconnection. In that regard, the description of the circuit will not be repeated here. The electrical loads 3, 13, 23 are each in Figure 2 as a series circuit of a plurality of light-emitting diodes, LEDs 30, 31; 32, 33; 34, 35 executed. The current sources 1, 20, 21 are each implemented in FIG. 2 with a respective current source transistor 36, the controlled path of which is connected between the respective tap nodes 4, 14, 24 and a resistor 37 connected to reference potential. The control input of the current source transistor 36 is connected to the output of a differential amplifier 38 having two inputs. One input is formed as a terminal for supplying a reference threshold, while the other input is connected to the load terminal of the transistor 36, which is connected to the resistor 37. The DC voltage regulator 10 is not shown in FIG. 2 for reasons of clarity.

Compared with a conventional current source, the current source 36, 37, 38 according to FIG. 2 is particularly advantageous with regard to stability and adjustability.

FIG. 3 shows another exemplary embodiment of a DC-DC converter for use in the circuits according to FIGS. 1 or 2. The actual DC / DC converter 39 has an input 40 for supplying an input voltage which drops with respect to reference potential 41. At the output 42, the supply voltage VDD is provided. The common signal line 8 is not directly connected to the feedback input 43 of the DC-DC converter. Rather, a low-pass filter, comprising a series resistor 44 and a downstream capacitance 45 connected to reference potential. This low-pass filter 44, 45 is connected via a coupling resistor 46 to the actual feedback input 43. In addition, a voltage divider 49 is provided which comprises a first resistor 47 and a second resistor 48. The first resistor 47 is connected between the output 42 and the feedback input 43. The second resistor 48 is connected between the feedback input 43 and a reference potential. The resistors 47, 48 have resistance values Rl, R2. The resistor 44 of the low-pass filter has the resistance R4. The capacity 45 of the low-pass filter has the capacitance value Cl. The coupling resistor 46 has the resistance value R3.

In order to stabilize the control loop, the low-pass filter comprising the components 44, 45 is used. These form the dominant pole in the transfer function of the control loop. The minimum output voltage VDD _MIN at the output 42 is set by the ratio of the resistance values Rl, R2. The maximum output voltage VDD _MAX at the output 42 is set by the values of the resistors Rl to R4. Vref is the voltage at node 43 that the DC / DC converter keeps constant.

The following rules apply:

VDD MIN = Vref - -

R

Accordingly, if, for example, one of the LED chains 30, 31; 32, 33; 34, 35 breaks, whereby the return voltage UV is forced to reference potential, yet the supply voltage VDD remains within the predetermined limits VDD _MIN and VDD _MAX .

Figure 4 shows another embodiment of the circuit of Figure 2. This corresponds to that largely in structure and advantageous interconnection and will not be described at this point again. The current branches, each comprising a current source, a comparator and a transistor, are each formed in pairs in FIG. 4 in pairs on common monolithically integrated chips 50, 51, 52. In the implementation according to FIG. 4, it becomes clear that despite the execution of the individual branches on different chips, a common signal line 8 can nevertheless be provided. There are no additional circuits needed.

Figure 5 shows a development of the circuit of Figure 4, in which the proposed principle is combined with the principle of selecting a minimum voltage. For this purpose, a minimum selection circuit 53, 54, 55 is provided on each of the chips 50 ', 51', 52 ', whose inputs are connected to the tap nodes of all branches on the respective chip. The output of the minimum selector 53, 54, 55 is connected to a common comparator 56, 57, 58 on each chip, whose output in turn drives a common transistor 59, 60, 61 on each chip. A load terminal of this transistor 59, 60, 61 is in turn connected to a common signal line 8 all chips 50 ', 51', 52 '. As a result, the flexibility can be further increased. Channels based on the selection of a minimum voltage can be arbitrarily combined with the proposed principle. FIG. 6 shows another development of the circuit of FIG. 4 with an example. The chips 50 ", 51", 52 "each have three branches in this example, each comprising a current source, a comparator and a transistor connected thereto. Each of the chips 50 'to 52' is configured to drive different types of electrical loads, for example, red diodes 62r, blue diodes 62b, and green diodes 62g. In this case, those branches which are designed to drive the red light-emitting diodes 62r are connected to a first common signal line 8r, while those branches which are designed to drive the blue diodes 62b are each connected to a second common signal line 8b via different chips , Those branches which are designed to drive the green LEDs 62g are connected to a third common signal line 8g. The red, blue and green diodes 62r, 62b and 62g are supply voltage side to each one associated supply voltage line, different for each type, for guiding different supply voltages

VDDB, VDDR, VDDG connected.

This serves, for example, in RGB applications in the control of color displays advantageous to group together different types of electrical loads and to control with equally grouped power sources, each have a common signal line 8r, 8b, 8g per type of electrical load.

Figure 7 shows the embodiment of the comparator 5 with downstream transistor 7 according to Figures 1, 2 and 4 to 6. Instead of this combination of comparator and transistor can in the figures 1, 2 and 4 to 6, for example, an arrangement according to Figure 8, 9 or 10 be turned on.

In FIG. 8, the comparator formed as OTA (operational transconductance amplifier-transconductance amplifier) 64 with a downstream current mirror 65 whose output transistor corresponds to the transistor 7 of FIG. 7 is characterized in particular by the small chip area requirement. With this circuit, a drain current is only delivered to the output 66, ie to the common signal line, if the voltage at the negative input 67 is smaller than that at the positive input 68. This is exactly the desired behavior of the control principle.

FIG. 9 shows a further development of the circuit of FIG. 8, likewise with an OTA 64 and a current mirror 65. However, additional current mirrors 69, 70, 71 are provided for their coupling to one another, resulting in an improved amplification factor and a better driver capability for the output transistor 72 to lead. To increase the gain, the transistor 65 may optionally be removed - as in the embodiment according to FIG. 8.

Instead of the embodiment of the tap node 4 between the electrical load 3 and the current source 1, as shown for example in FIGS. 1 and 2, the voltage tap may also be provided at the control input of the current source transistor 36 instead of at the load terminal of the current source transistor 36.

The circuit of Figure 10 is thus also an alternative to the formation of the current sources of Figures 2 and 4 to 6. The sampling of the voltage at the gate of the current source transistor as the tap node has the advantage that the gate voltage This transistor is monitored and is within a predetermined limited range, namely limited by the reference voltage Vg at the input of the comparator 5. This is particularly advantageous in view of manufacturing variations of the current source transistors. It should be noted that the inputs of the comparator 5 must be replaced. All circuit arrangements according to FIGS. 7 to 10 can, as shown in field effect transistor technology, eg. B. as MOSFETs, or alternatively be executed in bipolar technology.

The proposed principle is particularly advantageous for driving LED arrays in RGB or single colors. For example, the principle can be used in the following fields of application, namely general illumination, backlighting of liquid crystal display, LCD RGB

Screens and any lighting application in which multiple strands, each series circuits of light-emitting diodes comprising used.

LIST OF REFERENCE NUMBERS

1 power source

2 means for connecting an electrical load 3 electrical load

4 tap nodes

5 comparators

6 Connection for supplying a reference threshold

7 transistor 8r common signal line 8b common signal line 8g common signal line

9 reference potential connection

10 DC regulator 11 input

12 output

13 electrical load

14 picking knots

15 comparator 16 reference input

17 transistor

20 power source

21 power source

22 means for connecting an electrical load 23 electrical load

24 tap nodes

25 comparators

26 input for supplying a reference threshold 27 transistor 30 diode

31 diode

32 diode

33 diode 34 diode

35 diode

36 current source transistor

37 resistor 38 differential amplifier

39 DC voltage regulator

40 entrance

41 Reference potential connection 42 Output 43 Input

44 resistance

45 capacity

46 resistance

47 resistor 48 resistor

49 voltage divider

50 chip

51 chip

52 chip 53 minimum selection block

54 minimum selection block

55 minimum selection block

56 comparators

57 comparators 58 comparators

59 transistor

60 transistor

61 transistor 62r red LED 62b blue LED

62g green LED

64 OTA

65 current mirror Output Input Input Current mirror Current mirror Current mirror Transistor

Claims

claims

1. Current source arrangement, comprising

a current source (1), a means (2) for connecting an electrical load (3) connected to the current source (1),

a voltage tap node (4) coupled to the means (2) for connecting an electrical load,

a comparator (5) having a first input connected to the voltage tap node (4) and a second input arranged to supply a reference threshold (Vc),

a transistor (7) which is connected on the control side to an output of the comparator (5) and the load side to a signal line (8),

- A DC voltage regulator (10) having an input (11) for supplying an input voltage, having an output (12) connected to the means (2) for connecting the electrical load, and having a feedback input connected to the signal line (8 ) connected is.

2. Current source arrangement according to claim 1, characterized by

at least one further current source (20), at least one further means for connecting an electrical load (13) which is connected to the at least one further current source (20),

at least one further voltage tapping node (14) coupled to the at least one further means for connecting an electrical load (13),

at least one further comparator (15) having a first input, which is connected to the at least one further voltage tapping node (14), and having a second input arranged to supply at least one further reference threshold,

- At least one further transistor (17), the control side with an output of the at least one further comparator (15) and the load side is connected to the signal line formed as a common signal line (8).

3. Current source arrangement according to claim 2, characterized in that the reference threshold and the further reference threshold are the same.

4. Current source arrangement according to one of claims 1 to 3, characterized in that the electrical load comprises at least one light emitting diode (30).

5. Current source arrangement according to one of claims 1 to 3, characterized in that the electrical load comprises a series circuit a plurality of LEDs (30, 31).

6. Current source arrangement according to one of claims 1 to 5, characterized in that a means (53) for switching a smaller of at least two input voltages between at least two each with an associated current source and an associated means for connecting an electrical load coupled Spannungsabgriffsknoten and the first input of the comparator (56) is connected.

7. Current source arrangement according to one of claims 1 to 6, characterized in that for different types of electrical loads (62, 63) depending on a common signal line (8, 9) is provided.

8. Current source arrangement according to one of claims 1 to 7, characterized in that the current source comprises a current source transistor (36).

The current source arrangement according to claim 8, characterized in that the voltage tap node is coupled to the means for connecting an electrical load by the voltage tap node being formed at a control terminal of the current source transistor (36), the controlled path of the current source transistor (36) being in one common current path with the means (2) for connecting the electrical load is formed.

10. Current source arrangement according to claim 8 or 9, characterized in that - the current source transistor (36) with its controlled

Connected between the means (2) for connecting the electrical load and a resistor (37) connected against a reference potential terminal,

- A differential amplifier (38) is connected with its output to the control input of the current source transistor (36),

a first input of the differential amplifier (38) is designed to supply a reference voltage,

a second input of the differential amplifier (38) to the reference potential side terminal of the controlled path of

Current source transistor (36) is connected.

11. Current source arrangement according to one of claims 1 to 10, characterized in that the comparator (5) comprises a finite gain amplifier (64).

12. Current source arrangement according to claim 11, characterized in that the comparator (5) comprises a current mirror (65) whose input transistor is connected to an output of the amplifier (64) ^• , wherein the transistor of the Stromquellenanord- voltage, the load side with the signal line (8), which is the output transistor of the current mirror (65).

13. Current source arrangement according to claim 11 or 12, characterized in that the output of the operational amplifier is an unbalanced output, and in that current mirrors (69, 70, 71) are provided which connect a differential stage (64) of the operational amplifier to the unbalanced output.

14. Current source arrangement according to one of claims 1 to 13, characterized in that an electrical load (3) is connected to the means (2) for connecting the electrical load.

15. Current source arrangement according to one of claims 1 to 14, characterized in that the current source arrangement is monolithically integrated in semiconductor circuit technology.

16. Use of one or more current source arrangements according to one of claims 1 to 15 for the power supply matrix-arranged light-emitting diodes (62, 63) in a display device.

17. Use of at least one current source arrangement according to one of claims 1 to 15 for the power supply of light-emitting diodes (62r, 62b, 62g) each of a color type in a display device.

18. A method for operating an electrical load, characterized by the following steps:

Providing a supply current for the electrical load (3) with a current source (1),

Picking up a voltage dropping across the electrical load (3) and / or the current source (1) or a voltage derived therefrom,

Comparing the voltage thus determined with a reference threshold (Vc),

- driving a signal line (8) by means of a transistor (7) as a function of the comparison,

- Providing a supply voltage (VDD) for the electrical load (3) in response to an input voltage and a signal on the signal line (8).

19. The method according to claim 18, characterized by 'following steps:

Providing a further supply current for a further electrical load (13) with a further current source (20),

Picking up a voltage dropping above the further electrical load and / or the further current source, or a voltage derived therefrom, comparing the voltage thus determined with a further reference threshold, Activating the signal line (8) designed as a common signal line by means of a further transistor (17) as a function of the comparison,

- Providing the supply voltage (VDD) for the electrical load (3) and the further electrical load (13) in response to the input voltage and the signal on the common signal line (8).