WO2014053933A1

WO2014053933A1 - Current balancing for current-source-fed-loads

Info

Publication number: WO2014053933A1
Application number: PCT/IB2013/058526
Authority: WO
Inventors: Yuanqiang LIU; Jian Jiang; Ling Xu; Julyee ZHU; Dong Zheng
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-10-02
Filing date: 2013-09-13
Publication date: 2014-04-10

Abstract

Circuits (1) for balancing first and second currents flowing through first and second channels comprise first and second regulators (4, 7) for regulating amplitudes of the currents, and first and second sensors (5, 8) for sensing the amplitudes of the currents. Controllers (9) control the regulators (4, 7) in response to sensing results from the sensors (5, 8). This way, even in case a sum of the currents is supplied by one and the same current source (2), the first and second currents can be balanced. The first and second channels are parallel channels comprising serial connections of the loads (3, 6), the regulators (4, 7) and the sensors (5, 8). The regulators (4, 7) may possibly comprise transistors (41, 71), the sensors (5, 8) may possibly comprise resistors (51, 81), and the controller (9) may possibly comprise a comparator (91) and a transistor (92).

Description

CURRENT BALANCING FOR CURRENT-SOURCE-FED-LOADS

FIELD OF THE INVENTION

The invention relates to a circuit for balancing a first current flowing through a first channel and a second current flowing through a second channel, a sum of the first and second currents being supplied by a current source. The invention further relates to a device.

Examples of such a device are lamps and current sources and drivers for driving the first and second loads.

BACKGROUND OF THE INVENTION

US 2004 / 0233144 Al discloses a method and apparatus for driving light emitting diodes fed via a voltage source.

Loads such as light emitting diodes and other kinds of loads can alternatively be fed via a current source. When two loads in a parallel construction are fed via one and the same current source, current balancing may become an issue.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved circuit. It is a further object of the invention to provide an improved device.

According to a first aspect, a circuit is provided for balancing a first current flowing through a first channel and a second current flowing through a second channel, a sum of the first and second currents being supplied by a current source, the circuit comprising

- a first regulator for regulating a first amplitude of the first current,

- a first sensor for sensing the first amplitude of the first current, the first channel comprising a first serial connection of a first load and the first regulator and the first sensor,

- a second regulator for regulating a second amplitude of the second current,

- a second sensor for sensing the second amplitude of the second current, the second channel comprising a second serial connection of a second load and the second regulator and the second sensor, and

- a controller for in response to sensing results from the first and second sensors controlling the first and second regulators.

The controller receives the sensing results from both sensors and controls both regulators. As a result, the currents flowing through the parallel channels can be balanced, even under the condition that the sum of both currents is substantially equal to a total current that has a relatively constant amplitude and that is supplied by the current source.

The sensors may sense the amplitudes of the currents directly or may sense the amplitudes of the currents indirectly by sensing voltages indicative for the amplitudes of the currents.

An embodiment of the driver is defined by said controlling comprising a control of the first and second regulators in a mutually opposite way. Preferably, in case the first regulator increases the first amplitude of the first current, the second regulator will reduce the second amplitude of the second current, and vice versa.

An embodiment of the driver is defined by said sensing results being simultaneous sensing results. Both channels are preferably to be watched and to be controlled simultaneously.

An embodiment of the driver is defined by said controlling comprising, in response to a first sensing result from the first and second sensors indicating that the first amplitude of the first current is too large, reducing the first amplitude of the first current and increasing the second amplitude of the second current.

An embodiment of the driver is defined by said controlling comprising, in response to a second sensing result from the first and second sensors indicating that the first amplitude of the first current is too small, increasing the first amplitude of the first current and reducing the second amplitude of the second current.

An embodiment of the driver is defined by said controlling comprising, in response to a third sensing result from the first and second sensors indicating that the second amplitude of the second current is too small, increasing the second amplitude of the second current and reducing the first amplitude of the first current.

An embodiment of the driver is defined by said controlling comprising, in response to a fourth sensing result from the first and second sensors indicating that the second amplitude of the second current is too large, reducing the second amplitude of the second current and increasing the first amplitude of the first current.

An embodiment of the driver is defined by the first regulator comprising a first transistor, the first sensor comprising a first resistor, the second regulator comprising a second transistor, the second sensor comprising a second resistor, and the controller comprising a comparator having a first input coupled to the first resistor and having a second input coupled to the second resistor. An embodiment of the driver is defined by the first input being an inverting input, the second input being a non-inverting input, the controller further comprising a third transistor, and the comparator having an output coupled to a control electrode of the first transistor and to a control electrode of the third transistor, a first main electrode of the third transistor being coupled to a control electrode of the second transistor.

An embodiment of the driver is defined by the output being coupled to the first input via a third serial connection of a third resistor and a capacitor.

An embodiment of the driver is defined by the first main electrode of the third transistor being coupled to one side of a fourth resistor, another side of the fourth resistor being connectable to the current source.

An embodiment of the driver is defined by a first main electrode of the first transistor being connectable to the first load, a first main electrode of the second transistor being connectable to the second load, a second main electrode of the first transistor being coupled to one side of the first resistor and to the first input, a second main electrode of the second transistor being coupled to one side of the second resistor and to the second input, a second main electrode of the third transistor being coupled to ground, and the other sides of the first and second resistors being coupled to ground.

An embodiment of the driver is defined by the output being coupled to the control electrode of the third transistor via a fifth resistor. When two units are coupled, a third unit may be present in between, or not. This fifth resistor has a current limiting function.

According to a second aspect, a device is provided comprising the circuit as defined above and further comprising the first and second loads and/or the current source and/or a driver for driving the first and second loads. The circuit may form part of the first and second loads or of the current source or of the driver for driving these loads.

An embodiment of the device is defined by, when comprising the first and second loads, each one of the first and second loads comprising one or more light emitting diodes. The one or more light emitting diodes may be of whatever kind and in whatever combination. Especially for loads each comprising one or more light emitting diodes, current balancing may become an issue, for example to get the same light intensity per load.

An insight is that a current source provides a total current having a relatively constant amplitude and that, in case two parallel channels are to be connected to the current source, the total current will be divided over both channels. A basic idea is that a controller, in response to sensing results from first and second sensors, should control first and second regulators for regulating first and second amplitudes of the first and second currents. A problem to provide an improved circuit has been solved. A further advantage is that the circuit can be simple, low-cost and robust.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

Fig. 1 shows a circuit coupled to loads, and

Fig. 2 shows an embodiment of the circuit.

DETAILED DESCRIPTION OF EMBODIMENTS

In the Fig. 1, a circuit 1 coupled to loads 3, 6 is shown. The circuit 1 can balance a first current flowing through a first channel, comprising a first serial connection of a first load 3 and a first regulator 4 and a first sensor 5, and a second current flowing through a second channel, comprising a second serial connection of a second load 6 and a second regulator 7 and a second sensor 8. The first and second loads 3, 6 are coupled to a current source 2, that supplies a total current substantially equal to a sum of the first and second currents. The circuit 1 comprises the first regulator 4 for regulating a first amplitude of the first current, the first sensor 5 for sensing the first amplitude of the first current, the second regulator 7 for regulating a second amplitude of the second current, and the second sensor 8 for sensing the second amplitude of the second current. The circuit 1 further comprises a controller 9 for in response to sensing results from the first and second sensors 5, 8 controlling the first and second regulators 4, 7.

Preferably, said controlling comprises a control of the first and second regulators 4, 7 in a mutually opposite way. Further preferably, said sensing results are simultaneous sensing results.

In the Fig. 2, an embodiment of the circuit 1 is shown. The first regulator 4 comprises a first transistor 41, the first sensor 5 comprises a first resistor 51, the second regulator 7 comprises a second transistor 71, the second sensor 8 comprises a second resistor 81, and the controller 9 comprises a comparator 91 having a first input coupled to the first resistor 51 and having a second input coupled to the second resistor 81. The first input is an inverting input, and the second input is a non- inverting input. The controller 9 further comprises a third transistor 92. The comparator 91 has an output coupled to a control electrode (gate) of the first transistor 41 and coupled to a control electrode (basis) of the third transistor 92, for example via a fifth resistor 95. A first main electrode (collector) of the third transistor 92 is coupled to a control electrode (gate) of the second transistor 71.

The output of the comparator 91 is further coupled to the first input of the comparator 91 via a third serial connection of a third resistor 93 and a capacitor 96, which third serial connection has a timing parameter of for example 1 μβεα or 10 μβεα or 100 μβεΰ. without having excluded other values. The third serial connection of the third resistor 93 and the capacitor 96 provides feedback (proportional integral control) from the output of the comparator 91 to the first input of the comparator 91, but could alternatively be left out. The first main electrode (collector) of the third transistor 92 is coupled to one side of a fourth resistor 94, another side of the fourth resistor 94 is connectable to the current source 2.

A first main electrode (drain) of the first transistor 41 is connectable to the first load 3, here comprising one or more first light emitting diodes. A first main electrode (drain) of the second transistor 71 is connectable to the second load 6, here comprising one or more second light emitting diodes. The first and second loads 3, 6 are further connectable to the current source 2. A second main electrode (source) of the first transistor 41 is coupled to one side of the first resistor 51 and to the first input, and a second main electrode (source) of the second transistor 71 is coupled to one side of the second resistor 81 and to the second input. A second main electrode (emitter) of the third transistor 92 is coupled to ground, and the other sides of the first and second resistors 51 , 81 are coupled to ground as well.

The circuit 1 functions as follows. In case an amplitude of a voltage across the first resistor 51 is larger than an amplitude of a voltage across the second resistor 81 (this corresponds to a first sensing result from the first and second sensors 5, 8 indicating that the first amplitude of the first current is too large), the comparator 91 produces an output signal of a relatively low voltage amplitude. As a result, the first transistor 41 reduces the first amplitude of the first current. Further, the third transistor 92 reduces a third amplitude of a third current flowing through the third transistor 92 and through the fourth resistor 94, and this results in a voltage signal of a relatively high voltage amplitude being present at the control electrode (gate) of the second transistor 71. As a result, the second transistor 71 increases the second amplitude of the second current.

The same happens in case an amplitude of a voltage across the second resistor

81 is smaller than an amplitude of a voltage across the first resistor 51 (this corresponds to a third sensing result from the first and second sensors 5, 8 indicating that the second amplitude of the second current is too small). In case an amplitude of a voltage across the first resistor 51 is smaller than an amplitude of a voltage across the second resistor 81 (this corresponds to a second sensing result from the first and second sensors 5, 8 indicating that the first amplitude of the first current is too small), the comparator 91 produces an output signal of a relatively high voltage amplitude. As a result, the first transistor 41 increases the first amplitude of the first current. Further, the third transistor 92 increases a third amplitude of a third current flowing through the third transistor 92 and through the fourth resistor 94, and this results in a voltage signal of a relatively low voltage amplitude being present at the control electrode (gate) of the second transistor 71. As a result, the second transistor 71 reduces the second amplitude of the second current.

The same happens in case an amplitude of a voltage across the second resistor 81 is larger than an amplitude of a voltage across the first resistor 51 (this corresponds to a fourth sensing result from the first and second sensors 5, 8 indicating that the second amplitude of the second current is too large).

Any transistor 41 , 71 , 92 may be any kind of transistor. Any transistor 41, 71,

92 may be replaced by another transistor in a same connection or by another transistor in another connection or by a group of two or more transistors. The comparator 91 has a comparing function and may be replaced by another comparator or by one or more transistors. The third transistor 92 has an inverting function and may be replaced by another inverting element or by another transistor or by a group of two or more transistors. A combination of the comparator 91 and the third transistor 92 may be replaced by another comparing / inverting circuit and may be replaced by a group of two or more transistors. The first and second sensors 5, 8 may comprise further resistors in addition and may alternatively be realized through other kinds of current detectors. In case the inputs of the comparator 91 are interchanged, the output of the comparator 91 is to be connected to the control electrode of the second transistor 71 and for example via the fifth resistor 95 to the control electrode of the third transistor 92, and the first main electrode of the third transistor 92 is to be connected to the control electrode of the first transistor 41 etc. The fourth and fifth resistors 94, 95 may be replaced by other elements for limiting currents and/or for creating changing voltages etc.

A device may comprise the circuit 1 as defined above and may further comprise the first and second loads 3, 6 and/or the current source 2 and/or a driver for driving the first and second loads 3, 6. So, the circuit 1 may be sold as a solitary unit and may be sold as a part of a larger unit. The total current as supplied by the current source 2 is "substantially" equal to the sum of the first and second currents owing to the fact that via the fourth resistor 94 the third transistor 92 will draw some current too, but this third current will usually much smaller than the first and second currents. And even in case this third current disturbs the balance between the first and second currents, the circuit 1 will respond to that and restore the balance.

A voltage supply for feeding the comparator 91 may be realized in any possible way known to a person skilled in the art. And in each serial connection, two or more units may trade places. So, for example the load 3 (6) may alternatively be located between the regulator 4 (7) and the sensor 5 (8), or below that sensor 5 (8) etc.

Summarizing, circuits 1 for balancing first and second currents flowing through first and second channels comprise first and second regulators 4, 7 for regulating amplitudes of the currents, and first and second sensors 5, 8 for sensing the amplitudes of the currents. Controllers 9 control the regulators 4, 7 in response to sensing results from the sensors 5, 8. This way, even in case a sum of the currents is supplied by one and the same current source 2, the first and second currents can be balanced. The first and second channels are parallel channels comprising serial connections of the loads 3, 6, the regulators 4, 7 and the sensors 5, 8. The regulators 4, 7 may possibly comprise transistors 41, 71, the sensors 5, 8 may possibly comprise resistors 51, 81, and the controller 9 may possibly comprise a comparator 91 and a transistor 92.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A circuit (1) for balancing a first current flowing through a first channel and a second current flowing through a second channel, a sum of the first and second currents being supplied by a current source (2), the circuit (1) comprising

- a first regulator (4) for regulating a first amplitude of the first current,

- a first sensor (5) for sensing the first amplitude of the first current, the first channel comprising a first serial connection of a first load (3) and the first regulator (4) and the first sensor (5),

- a second regulator (7) for regulating a second amplitude of the second current,

- a second sensor (8) for sensing the second amplitude of the second current, the second channel comprising a second serial connection of a second load (6) and the second regulator (7) and the second sensor (8), and

- a controller (9) for in response to sensing results from the first and second sensors (5, 8) controlling the first and second regulators (4, 7).

2. The circuit (1) as defined in claim 1, said controlling comprising a control of the first and second regulators (4, 7) in a mutually opposite way.

3. The circuit (1) as defined in claim 2, said sensing results being simultaneous sensing results.

4. The circuit (1) as defined in claim 3, said controlling comprising, in response to a first sensing result from the first and second sensors (5, 8) indicating that the first amplitude of the first current is too large, reducing the first amplitude of the first current and increasing the second amplitude of the second current.

5. The circuit (1) as defined in claim 4, said controlling comprising, in response to a second sensing result from the first and second sensors (5, 8) indicating that the first amplitude of the first current is too small, increasing the first amplitude of the first current and reducing the second amplitude of the second current.

6. The circuit (1) as defined in claim 3, said controlling comprising, in response to a third sensing result from the first and second sensors (5, 8) indicating that the second amplitude of the second current is too small, increasing the second amplitude of the second current and reducing the first amplitude of the first current.

7. The circuit (1) as defined in claim 6, said controlling comprising, in response to a fourth sensing result from the first and second sensors (5, 8) indicating that the second amplitude of the second current is too large, reducing the second amplitude of the second current and increasing the first amplitude of the first current.

8. The circuit (1) as defined in claim 1, the first regulator (4) comprising a first transistor (41), the first sensor (5) comprising a first resistor (51), the second regulator (7) comprising a second transistor (71), the second sensor (8) comprising a second resistor (81), and the controller (9) comprising a comparator (91) having a first input coupled to the first resistor (51) and having a second input coupled to the second resistor (81).

9. The circuit (1) as defined in claim 8, the first input being an inverting input, the second input being a non-inverting input, the controller (9) further comprising a third transistor (92), and the comparator (91) having an output coupled to a control electrode of the first transistor (41) and to a control electrode of the third transistor (92), a first main electrode of the third transistor (92) being coupled to a control electrode of the second transistor (71).

10. The circuit (1) as defined in claim 9, the output being coupled to the first input via a third serial connection of a third resistor (93) and a capacitor (96).

11. The circuit (1) as defined in claim 9, the first main electrode of the third transistor (92) being coupled to one side of a fourth resistor (94), another side of the fourth resistor (94) being connectable to the current source (2).

12. The circuit (1) as defined in claim 9, a first main electrode of the first transistor (41) being connectable to the first load (3), a first main electrode of the second transistor (71) being connectable to the second load (6), a second main electrode of the first transistor (41) being coupled to one side of the first resistor (51) and to the first input, a second main electrode of the second transistor (71) being coupled to one side of the second resistor (81) and to the second input, a second main electrode of the third transistor (92) being coupled to ground, and the other sides of the first and second resistors (51, 81) being coupled to ground.

13. The circuit (1) as defined in claim 9, the output being coupled to the control electrode of the third transistor (92) via a fifth resistor (95).

14. A device comprising the circuit (1) as defined in claim 1 and further comprising the first and second loads (3, 6) and/or the current source (2) and/or a driver for driving the first and second loads (3, 6).

15. The device as defined in claim 14 when comprising the first and second loads (3, 6), each one of the first and second loads (3, 6) comprising one or more light emitting diodes.