DE102015119241B4 - Current control circuit and circuitry therewith - Google Patents

Abstract

Current control circuit (30) for distributing a current from a common current source (P1) to a multiplicity of parallel consumer networks (40) with a predetermined current division ratio, the current control circuit (30) for each of the consumer networks (40) having:a power transistor (T1) , in particular field effect transistor, preferably MOSFET, in series with the load network (40);a load resistor (R2) in series with the power transistor (T1) on its side facing away from the load network (40), between the load resistor (R2) and the power transistor (T1) a working potential (V3) is defined;a control resistor (R4), one side of which is connected to a control reference potential (V6) which is uniform for the entire current control circuit (30);a control transistor (T2), in particular a bipolar transistor, which is connected in a between the working potential (V3) and the other side of the St, remote from the control reference potential (V6). is connected to a current path formed by a resistor (R4), the control electrode, in particular the base (b), of the control transistor (T2) being connected to the control electrodes, in particular bases, of the control transistors (T2) of all other load networks (40) in order to connect all control transistors ( T2) common base potential (V7) coupled to the current paths between the control transistor (T2) and the control resistor (R4);and wherein a control electrode of the power transistor (T1) is connected to the current path between the control transistor (T2) and the control resistor ( R4), which are provided for exactly one other of the consumer networks (40), is connected.

Description

The present invention relates to a current control circuit and a circuit arrangement with the current control circuit and a multiplicity of parallel consumer networks, each of which has a multiplicity of series-connected light-emitting diodes. The current control circuit serves to distribute a current from a common current source to the multiplicity of consumer networks with a predetermined current division ratio.

In optical inspection devices, in particular in optical spectrometers, circuits are used in which a number of light sources, each comprising a number of diodes, emit light with as much predefined light intensity as possible, in particular the same light intensity. A predetermined current is supplied with an external constant current source. So that the same current flows through all diodes, it is generally desirable to arrange all diodes in a single current path. However, this is not always possible, because since the voltage drop across the individual diodes (approx. 3 to 4V) would add up in each case, the total supply voltage required increases considerably. For approval reasons, however, one does not want to use voltages above 48V. It may therefore be necessary to distribute the diodes over several current branches connected in parallel. The accuracy of the distribution of the total supply current to the current branches over a wide current range (e.g. for dimming the brightness) is important.

Controlling the current through diodes is not easy because the behavior of diodes is extremely non-linear. The hotter a diode gets, the better it conducts. As a result, it draws more current, which would make it even hotter. Active control of the current is therefore necessary.

From the US 2007/0 080 911 A1 a controller circuit for light-emitting diodes (LED) emerges. An LED array has at least a first row of LEDs connected in parallel, each containing at least two LEDs.

In the US 2014/0 062 314 A1 discloses a current sharing circuit for LED lighting to provide active current sharing in lighting applications.

From the WO 2011/150 772 A1 discloses a multi-branch light emitting diode current balancing control circuit. It includes a constant current source and a plurality of light-emitting diode branches, each light-emitting diode branch corresponding to a control circuit.

In the WO 2014/053 933 A1 discloses power balancing for loads powered by a power source.

From the JP 2013-157493A discloses an LED driver circuit capable of balancing drive currents flowing through LEDs of a plurality of LED strings connected in parallel to a constant current source.

For the application described, it is known to use a current mirror in which one branch of the LED chain mirrors the current of the other branch. However, after the printed circuit board has been produced, a decision must be made as to which branch is the reference in order to then operate the other mirrored. The decision as well as the dimensioning of the mirroring is set manually with the help of jumpers after production.

A few circuit proposals of this type for current mirrors are known in the prior art, but none of them allow for automatic current division, with which manual calibration after production is no longer necessary. While circuit proposals for current dividers exist, none have been identified that are usable for large current applications of the above requirements.

• - eine automatische Stromteilung;
• - eine Verbesserung der Genauigkeit;
• - Robustheit (beispielsweise gegenüber Stromstärke und Schaltungselement-Toleranzen);
• - gutes dynamisches Verhalten (insbesondere beim Ein- und Ausschalten, sowie im Pulsbetrieb);
• - Einfachheit im Aufbau;
• - Wiederverwertbarkeit des gleichen LED-Ketten-Aufbaus wie in den bisherigen Beleuchtungen, sowie der gleichen Leistungstransistoren;
• - hohe Effizienz (insbesondere kleine Verlustleistung der Regelschaltung)
• - Anpassbarkeit an ungleiche Stromteilungsverhältnisse über einen weiten Bereich; sowie
• - Erweiterbarkeit auf mehrere (mehr als zwei) LED-Ketten-Zweige.

It is therefore an object of the present invention to provide a current control circuit for distributing a current from a common current source into a plurality of parallel current branches with a predetermined current division ratio of respective supply currents in the current branches in order to supply a respective consumer network in each current branch with the respective supply current that meets at least one of the following requirements:

• - an automatic current division;
• - an improvement in accuracy;
• - robustness (e.g. to current and circuit element tolerances);
• - Good dynamic behavior (especially when switching on and off, as well as in pulse mode);
• - Simplicity in construction;
• - Recyclability of the same LED chain structure as in the previous lighting, as well as the same power transistors;
• - high efficiency (especially small power loss of the control circuit)
• - Adaptability to unequal current sharing ratios over a wide range; such as
• - Expandability to multiple (more than two) LED chain branches.

The object is solved by the features of the independent claims. Advantageous further developments and embodiments form the subject matter of the dependent claims.

According to one aspect of the present invention, a current control circuit for distributing a current from a common current source to a plurality of parallel load networks with a predetermined current sharing ratio is provided. Each of the consumer networks has, in particular, a large number of light-emitting diodes connected in series. For each of the consumer networks, the current control circuit has a self-locking power transistor, in particular a field effect transistor, preferably a MOSFET, in series with the consumer network; a load resistor in series with the power transistor on its side facing away from the load network, with a load potential being defined between the load resistor and the power transistor; a control resistor, one side of which is connected to a control reference potential that is uniform for the entire current control circuit, a control transistor, in particular a bipolar transistor, which is connected in a current path formed between the working potential and the other side of the control resistor that is remote from the control reference potential. In this case, the control electrode of the control transistor is connected to the control electrodes of the control transistors of all other consumer networks in order to form a base potential common to all control transistors. A control electrode of the power transistor is connected to the current path between the control transistor and the control resistor provided for exactly one other of the load networks.

In this current control circuit, the current through the individual consumer networks is detected by means of the load resistors and coupled to the power transistor of another consumer network by means of the control transistors. The ratio of the currents through the individual consumer networks is regulated independently by this cross-coupling or negative feedback.

The common base potential can be coupled to the current paths between the control transistor and the control resistor by means of control diodes, one control diode being arranged between each current path between the control transistor and the control resistor and the base potential. A gate potential for driving the respective power transistor of the other consumer network is present in this current path. Due to the coupling of the base potential by means of the control diodes, the base potential is coupled to the respectively highest gate potential of all consumer networks.

The control electrodes of all current branches are preferably connected to one another and form a reference working potential which is connected to the base potential by means of a balancing resistor.

Furthermore, the current control circuit can have a zener diode which is connected between the control reference potential and a potential defined by the sides of the load resistors which are connected to one another and are remote from the respective power transistor.

For the purposes of the present invention, a plurality is a number of two or more. The plurality of consumer networks is preferably two, three or four. In the context of the invention, a consumer network is any circuit that requires a current supply and causes a voltage drop. The consumer network preferably has a series connection of a large number of light-emitting diodes, ie a so-called LED chain. However, the application of the invention is not limited to the supply of LED chains. A conductor section can be designed in any desired way, for example as a conductor track, connection pad or potential well on a printed circuit board, a cable, a busbar, stranded wire or the like. If, in the context of the invention, a certain, concretely named potential is spoken of in the physical sense, this is to be understood as meaning a conductor section that has the so-called has potential. This means that if a circuit element is connected to a potential, this is to be understood within the meaning of the invention in such a way that the circuit element is connected to the conductor section that has the potential. When two circuit elements are described as parallel, this is to be understood in the sense of the invention that the circuit elements are connected in parallel between a first conductor section (a first potential) and a second conductor section (a second potential). In terms of the invention, a current sink potential is a potential that is lower than an input potential of a circuit. Specifically, the current sink potential can be a collective sink potential of a circuit arrangement with the load networks and the current control circuit. In particular, but not necessarily, the current sink potential is identical to the zero potential (the "ground") of the current source. However, the current sink potential can also be decoupled from the zero potential by an ohmic resistor. According to the invention, a control reference potential is an external potential which is the same for the entire current control circuit, ie for all branches of the current control circuit, and which is decoupled from the consumer networks by an ohmic resistor (scaling resistor). When a circuit element is considered to be connected in a current path, or in series, it refers to the connection of the main electrodes (source/drain for a field effect transistor and collector/emitter for a bipolar transistor) in the current path for a transistor, or the two for two-terminal circuit elements Poles. Unless otherwise stated, identically named circuit elements in all branches of the current control circuit can be understood as having the same dimensions.

The current control circuit described above automatically distributes the current to the multiplicity of parallel consumer networks in such a way that a specified current division ratio can be maintained with high accuracy and stability. The current control circuit is simple in structure and can be applied to two or more consumer networks. It is robust against current strength and circuit element tolerances and has good dynamic behavior and low power dissipation. With the same working resistances, an even current sharing ratio between all consumer networks (50:50 with two consumer networks) can be achieved. The circuit allows reuse of the power transistors from conventional current control circuits and requires no further changes to the design of existing LED strings provided in the consumer networks.

According to the present invention, the control transistor can be a bipolar transistor. These can be constructed as an npn transistor or as a pnp transistor. Depending on the design of the control transistor, the sequence and polarization of the circuit elements of the current control circuit may need to be adapted to one another and to the consumer networks.

If the control transistor is an npn transistor, the load networks are provided on the side of a common main supply potential supplied by the current source and the load resistors are connected to a common current sink potential. In each case (i.e., with respect to each one of the consumer networks), the working potential is a source potential of the power transistor and connected to an emitter of the control transistor, the control electrode of the power transistor assigned to one consumer network is connected to the collector of the control transistor assigned to another consumer network, is the The control resistor is connected to the collector of the control transistor, the control reference potential is connected to the main supply potential via a scaling resistor, and the control diode is connected in such a way that its flow direction points to the reference working potential. Furthermore, the zener diode is connected in such a way that its flow direction points from the current sink potential to the control reference potential.

If the control transistor is a pnp transistor, the load resistors are connected to a common main supply potential supplied by the current source and the consumer networks are provided on the side of a common current sink potential. In each case (i.e., with respect to each one of the consumer networks), the working potential is a drain potential of the power transistor and connected to a collector of the control transistor, the control electrode of the power transistor assigned to one consumer network is connected to the emitter of the control transistor assigned to another consumer network, the The control resistor is connected to the emitter of the control transistor, the control reference potential is connected to the current sink potential via a scaling resistor, and the control diode is connected so that its flow direction points away from the reference working potential. Furthermore, the zener diode is connected in such a way that its flow direction points from the main supply potential to the control reference potential.

In a development, a compensating capacitor is connected in parallel with the compensating resistor. The dynamic behavior of the current control circuit can be optimized by dimensioning the compensation capacitor.

Preferably the power source is a direct current source. Alternatively, the current source can be a pulsed current source.

In a preferred embodiment, the working resistors are fixed resistors. The current division ratio can be determined by dimensioning the working resistors.

In an alternative embodiment, the load resistors are variable resistors (i.e., potentiometers). This allows the current sharing ratio to be adjusted.

The working resistors therefore have in particular a resistance ratio to one another which can be selected in accordance with the predetermined current division ratio.

The predetermined flow sharing ratio can be either a uniform or an uneven flow sharing ratio.

The supply voltage, which results from a difference between the main supply potential and the current sink potential, is preferably less than or equal to a predetermined limit value. The predetermined limit can be 48 V, for example, which facilitates the approval of a device equipped with the circuit. Depending on the legal or voluntary industrial requirements, the specified limit value can also be selected differently in other or changed legislation and/or technical contexts.

According to a further aspect of the present invention, a circuit arrangement with a multiplicity of parallel consumer networks, each of which in particular has a multiplicity of series-connected light-emitting diodes, and a current control circuit for distributing a current from a common power source to the multiplicity of parallel consumer networks with a provided predetermined current sharing ratio. According to the invention, the current control circuit is constructed as described above.

In a preferred embodiment, the consumer networks are constructed identically, in particular with an identical number of light-emitting diodes of identical type.

• 1 zeigt eine Schaltungsanordnung mit einer Stromsteuerschaltung gemäß einem ersten Ausführungsbeispiel der vorliegenden Erfindung.
• 2 zeigt eine Schaltungsanordnung mit einer Stromsteuerschaltung gemäß einem zweiten Ausführungsbeispiel der vorliegenden Erfindung.
• 3 zeigt eine Schaltungsanordnung mit einer Stromsteuerschaltung gemäß einem dritten Ausführungsbeispiel der vorliegenden Erfindung.

Other objects, features, characteristics and advantages of the present invention will become clearer from the description of preferred embodiments illustrated in the attached figures.

• 1 shows a circuit arrangement with a current control circuit according to a first embodiment of the present invention.
• 2 shows a circuit arrangement with a current control circuit according to a second embodiment of the present invention.
• 3 shows a circuit arrangement with a current control circuit according to a third embodiment of the present invention.

The figures are schematic circuit diagrams in the usual symbolic representation of the circuit elements. In the figures, for the sake of clarity, reference numbers may have an alphabetical prefix depending on the type of circuit element or physical quantity referred to. In the circuit arrangements shown, a prefix C denotes a capacitor, a prefix D denotes a diode, a prefix P denotes a current source, a prefix R denotes an ohmic resistor, a prefix T denotes a transistor, a prefix U denotes an electric voltage and a prefix V denotes an electric potential. The counting of the circuit elements or physical variables with a specific prefix, ie within a specific group of circuit elements or physical variables, is of a functional nature and is not intended to be an indication of the number of circuit elements in the circuit arrangement. In contrast to the usual representation in circuit diagrams, in which each individual circuit element has its own counter, in the figures presented here all circuit elements with the same or comparable function have the same counter. It is possible, possibly also preferable, but not mandatory in every case, for circuit elements with the same counter to be of the same type tion and/or dimensioning. It should also be pointed out that physical quantities that are provided with the same reference symbols in the figures can be variable and can assume different values at different points in the circuit arrangement, but this does not always have to be the case.

To simplify the description and understanding, it is assumed here that all conductor sections of the circuit arrangements shown are comparatively short and at least essentially free of potential losses. Thus, a conductor section that extends between two or more circuit elements can be addressed by its potential, which is assumed to be constant. If, for example, it is described below that a circuit element is connected to a specific potential, this should be read in such a way that the circuit element is connected to that conductor section which is addressed by the specific potential.

1 shows a circuit arrangement 100 with a current control circuit 30 according to a first embodiment of the present invention.

According to the illustration in 1 In the circuit arrangement 100, a supply circuit 10 (circled in dash-dotted lines in the figure), two parallel current branches 20 which are supplied with current by the supply circuit 10, and a current control circuit 30 (circled in dash-dotted lines in the figure) are provided.

The supply circuit 10 has a current source P1 whose negative pole is connected to a zero potential V0 and whose output potential is led via a series resistor R1 to a main supply potential V1 that is common to all current branches 20 and the current control circuit 30 .

Each current branch 20 branches off from the main supply potential V1 and each has a consumer network 40 (circled in the figure by dot-dashed lines). Each consumer network 40 has a large number of series-connected light-emitting diodes D1. It should be noted that the load networks 40 can be arranged on the same circuit board as the other parts of the circuit arrangement or alternatively can be provided externally and integrated into the circuit arrangement 100 by means of connection terminals 60 or the like. A voltage drop U1 occurs at each of the light-emitting diodes D1 of the consumer networks 40, so that a consumer potential V2 prevails at an output of the consumer networks 40 in each case.

Since the individual voltage drops U1 can be different due to the non-linearity of the LEDs D1 described above, experience has shown that a different consumer potential V2 will occur in each current branch 20, which is why the currents I in the consumer networks 40 can be different without active current control. The current control circuit 30 serves to control the supply currents I divided into the current branches 20 in each case from the main supply potential V1 with a predetermined, here uniform, current division ratio. The current control circuit 30 has two control branches 50 which are each assigned to one of the current branches 20 and have both circuit elements in the respectively assigned current branch 20 and circuit elements outside of the respectively assigned current branch 20 .

A power transistor T1 and a load resistor R2, which are connected in series in the specified order in the respective current branch 20 downstream of the load network 40, form essential components of the current control circuit 30. The power transistor T1 is a normally-off field effect transistor, more precisely a normally-off MOSFET, where however, the scope of the invention is not limited to this particular case. The power transistor (MOSFET) T1 thus has a source s and a drain d as main electrodes and a gate g as control electrode. In this case, the drain d of the respective power transistor T1 is connected to the downstream end of the respective load network 40 and is therefore at the load potential V2. The source s of the power transistor T1 is connected to one side of the respective working resistor R2 and thus defines a working potential V3 for the working resistor R2. The other end of the load resistor R2 is connected to a sink potential V4 common to all current branches 20 . In the present exemplary embodiment, the current sink potential V4 is identical to the zero potential V0 of the current source P1, but in principle it can be any potential that is a suitable sink for the supply current (i.e. with respect to the main supply potential V1, taking into account the consumers that occur). A voltage drop U2 occurring across the working resistor R2 is, as will be described in more detail later, an essential variable for the control of the partial currents in the current branches 20.

The current control circuit 30 also branches off from the main supply potential V1 and initially has a scaling resistor R3 in order to scale the main supply potential V1 to a relatively lower main control potential V6, from which each control branch 50 is supplied. The main control potential V6 is also connected to the common current sink potential V4 via a zener diode D3 switched in the blocking direction. In other words, this also means that the sink-side sides of the working resistors R2 of the current branches 20 are connected to the common main control potential V6 of the control branches 50 via the Zener diode D3. Each control branch 50 is connected to the main control potential V6 via a control resistor R4. A control transistor T2 is provided downstream of the control resistor R4. In the present exemplary embodiment, the control transistor T2 is a bipolar transistor (BPT), more precisely an npn transistor. In other words, the control transistor T2 has a collector c and an emitter e as main electrodes and a base b as a control electrode. The collector c of the control transistor T2 is connected to the control resistor R4, and the emitter of the control transistor T2 is connected to the working potential V3 of the current branch 20 in question. The working voltage U2 is tapped off as a voltage drop across the working resistor R2 via the emitter e of the control transistor T2, since this voltage drop corresponds to the difference between the working potential V3 and the common current sink potential V4. This is significant for the current control since the voltage drop across the working resistor R2, and consequently the working voltage U2 and thus the working potential V3, is proportional to the current I flowing in the respective current branch 20.

The bases b of the control transistors T2 of the two control branches 50 are connected to one another and thus have a common base potential V7, via which they are supplied with current. For this purpose, the collector sides c of all control branches 50 are connected via a respective control diode D2 to a common main control potential V8, which in turn is led to the common base potential V7 via a parallel connection of a compensation capacitor C1 and a compensation resistor R5.

The current control circuit 30 is completed in that the collector side c of the control transistor T2 of the control branch 50 associated with a current branch 20 is connected to the gate g of the power transistor T1 of the other current branch 20 in each case.

C1

3 pF,

D1

LXK 2 - PW 14 (vorgegebener LED-Typ)

D2

1N914 (alternativ: 1/2 BAW 56),

D3

Z-Diode 15 V / 0,5 W (DFLZ33),

P1

PULSE (0 mA - 2000 mA für 1 µs - 1 µs bzw. 1 µs - 20 µs bzw. 140 µs -1s)

R1

0,001 Ω

R2

1 Ω,

R3

1 kΩ,

R4

10 kΩ,

R5

50 kΩ,

T1

PMV 31 XN

T2

BC547B (alternativ: BCM e 847 DS)

The following typifications and dimensionings can be specified as an example combination of circuit elements:

C1

3 pF,

D1

LXK 2 - PW 14 (default LED type)

D2

1N914 (alternatively: 1/2 BAW 56),

D3

Zener diode 15 V / 0.5 W (DFLZ33),

P1

PULSE (0 mA - 2000 mA for 1 µs - 1 µs or 1 µs - 20 µs or 140 µs -1s)

R1

0.001Ω

R2

1Ω,

R3

1kΩ,

R4

10kΩ,

R5

50kΩ,

T1

PMV 31 XN

T2

BC547B (alternative: BCM e 847 DS)

The properties of the specified types can be found in the manufacturer's relevant data sheets and are therefore not explained in detail here.

The automatic control of the currents I of the current branches 20 takes place with the circuit arrangement described above as follows.

As described above, the working potential V3 of each current branch 20 is tapped off by means of an emitter circuit with the two control transistors T2. The two control transistors are supplied with the same base potential V7. Depending on the voltage drops U2 over the working resistance stands R2, so ultimately depending on the working potentials V3, a base current is distributed over the control transistors T2.

Since the collector sides of the control transistors T2 are connected to the gate of a power transistor T1 of the respective other current branch 20, an increase in the working potential V3 of a current branch 20 is amplified via the respective control transistor T2, as a result of which the current flow in the respective other current branch 20 is increased.

With this cross-coupling, the current I in one of the current branches 20 is tapped off as the working potential V3, amplified and used to control the current flow in the other current branch 20.

The "amplification" is carried out by reducing the potential difference (V7 - V3) between the base and the emitter at the control transistor T2 with an increase in the working potential V3, so that the electrical resistance of the transistor T2 between the collector side c and the emitter side e increases, which also increases the voltage drop between the collector side c and the emitter side e. This additional voltage drop is added to the increased working potential V3 and forms the gate potential V5, with which the power transistor T1 of the respective other current branch 20 is driven. Thus, an increase in the current in one current branch 20 leads to an increase in the current in the other current branch 20. Since the two resistors R2 of the two current branches are identical in the present exemplary embodiment, the two currents in the two current branches 20 are regulated to the same value. The ratio of the currents is set in the ratio of the two resistors R2. By changing the two resistors R2, the ratio of the currents in the two current branches can be changed accordingly. In principle, one or both resistors R2 can also be formed by a potentiometer, so that the current ratio can be freely adjusted.

It should be noted that once the gate potential V5 of a power transistor T1 has increased over a certain range, it is difficult to counteract and rebalance.

The gate potential V5 of the power transistors T1 is therefore set to the reference working potential V8 by means of the control diodes D2, with the reference working potential V8 corresponding to the higher of the two amplified working potentials V3 that form the gate potentials V5 of the power transistor T1. A base current for the control transistors T2 is generated from the main control potential V8 via the compensating resistor R5. This has the effect that the greater the main control potential V8, the greater the base current at the control transistors T2 and the more these transistors T2 conduct. As a result, more voltage drops across the upstream control resistors R4. The control resistors R4 are preferably adjusted in such a way that the gate voltage at the power transistors T1 cannot exceed a predetermined limit value, which in the present case is approximately 1V.

In the control branch 50, the voltage is limited by the zener diode D3 to a suitable value of about 33V or so. This ensures a constant behavior of the circuit independent of the potential difference V1-V4 and thus independent of the total current of the current source P1.

As in 1 shown, one of the consumer networks 40 (in Fig 1 the right-hand consumer network 40) has one light-emitting diode D1 more than the other consumer network 40. The additional light-emitting diode D1 is separated from the other light-emitting diodes D1 by a further connection terminal 60. From the two connection terminals 60 which bracket the additional light-emitting diode D1, a stub line branches off in each case and leads to a further connection terminal 60 in each case, via which the additional light-emitting diode D1 can be bridged. The additional light-emitting diode D1 can be used, for example, to check the current flow or, for example by connecting or bridging the additional light-emitting diode D1, to test the control circuit.

The circuit concept separates the power control with the power transistors T1 from the regulation of the current intensity, which is implemented with a pair of control transistors T2, T2. This results in a high control gain, which results in very precise current division/mirroring. The control transistor pair T2, T2 works with coupled bases as a differential amplifier. The amplified current difference, which is tapped off as a voltage by means of the emitters e across the working resistors R2, is then applied to the gates g of the power transistors T1 via the collector outputs c. In the actual implementation, the power transistors T1 were taken over from an existing LED circuit as self-locking MOSFETs. These are so-called "digital power transistors" that have a small gate voltage range from blocking to switching on (high gain of the gate voltage on the MOSFET on-resistance).

1. 1. Auskopplung einer Konstant-Spannung V3 mittels der Zener-Diode D3
2. 2. Rückkopplung der Kollektorspannungen auf die Basis des NPN-Paars T2, T2 mittels der Dioden D2, D2.

A special feature of the present invention lies in the definition of the reference working potential V8 (also referred to as the reference working point), since the supply voltage in the application varies over a wide range in order to be able to dim the LED strands. The reference operating point is stabilized in order to obtain a high control gain. The working point stabilization is achieved by two measures:

1. 1. Extraction of a constant voltage V3 by means of the zener diode D3
2. 2. Feedback of the collector voltages to the base of the NPN pair T2, T2 by means of the diodes D2, D2.

It goes without saying that the person skilled in the art will be able to suitably adapt the circuit arrangement depending on the type and number of LEDs used (specification D1) and to select suitable circuit elements.

2 shows a circuit arrangement 200 with a current control circuit 30 according to a second embodiment of the present invention.

According to the illustration in 2 a supply circuit 10, four parallel current branches 20, which are supplied with current by the supply circuit 10, and a current control circuit 30 are provided in the circuit arrangement 200.

Unlike the circuit arrangement 100 of the first exemplary embodiment, the current control circuit 30 does not have two but four control branches 50, corresponding to the number of current branches 20 to be supplied and controlled. Otherwise, what was said for the previous exemplary embodiment applies to the structure and interconnection of each of the circuit parts 10, 20, 30, 40, 50, so that a renewed description is dispensed with in order to avoid repetition. For reasons of clarity, in 2 the circuit parts 10, 30, 40 are not redrawn.

For clarity, it is pointed out that all current branches 20 as well as the current control circuit 30 branch off from the main supply potential V1 supplied by the supply circuit 10, all control branches 50 branch off from the potential V6 supplied by the scaling resistor 50, the bases of all four control transistors T2 on the common base potential V7 lead and the gate of the power transistor T1 of each current branch 20 is connected to the collector of the control transistor T2 of exactly one control branch 50 assigned to another current branch 20 .

In other words, in this exemplary embodiment, four consumer networks 40 are provided, in each of which a plurality of light-emitting diodes D1 are arranged. The individual current branches 20 with the respective consumer network 40 are coupled in a circular manner via a respectively assigned control branch 50 of the current control circuit 30 . Otherwise, this circuit arrangement 200 works in exactly the same way as with two current branches 20.

The more current branches 20 there are, the more difficult and sensitive stable current control becomes. Simulations have shown that the currents in three or four current branches can be regulated well with the circuit concept according to the invention.

3 shows a circuit arrangement 300 with a current control circuit according to a third embodiment of the present invention.

In the 3 The circuit arrangement 300 shown in this exemplary embodiment is the one shown in FIG 1 The circuit arrangement 100 shown in the first exemplary embodiment is functionally equivalent, with the difference that a PNP transistor is used as control transistor T2 instead of an NPN transistor, and a PMOS power transistor T1 is used instead of the NMOS power transistor. This fundamental difference requires a reversal of the circuit structure, ie the order of the circuit elements. In each current branch 20, the working resistor R2 is initially at the main supply potential V1, followed by the self-locking power transistor T1 with drain d and then at its source s the consumer network 40, which finally falls to the current sink potential V4. The working potential V3 is tapped off at the source s of the power transistor T1 and is at the emitter e of the control transistor (PNP transistor) T2, whose collector c falls to the common main control potential V6 via the control resistor R4. Of the Scaling resistor R3 leads the common main control potential V6 to the current sink potential V4. The control diode D2 leads from the common reference working potential V7 to the emitter side e of the respective control transistor T2, and the gate g of the power transistor T1 is also located on the emitter side e of the control transistor T2 of the other current branch 20. The zener diode points from the main supply potential V1 to the main control potential V6

In other words, the working potential V3 of each current branch 20 is tapped off here by means of a collector circuit with the two control transistors (pnp transistors) T2, unlike in the case of control by npn transistors. The two control transistors are supplied with the same base potential V7. Depending on the voltage drops U2 across the working resistors R2, ie ultimately depending on the working potentials V3, a base current is distributed across the control transistors T2.

Thus, the current control circuit 30 operates basically the same as in the first embodiment, only with the arrangement direction reversed. A detailed description of the mode of operation is therefore omitted in order to avoid repetition; instead, reference is made to the description of the first exemplary embodiment, which is to be applied analogously. It should also be noted that the working voltage U2 results here as the difference between the main supply potential V1 and the working potential V3, which occurs here as the source potential of the power transistor T1.

The circuit arrangements 100, 200, 300 are basically intended for direct current operation. Simulations have shown that they can also be operated in pulsed mode. The circuits show good dynamic behavior.

Different current distributions in the individual current branches 20 can be set with different working resistances R2. The working resistors R2 can also be embodied by potentiometers, so that the current flow in the individual current branches 20 can be set individually by hand.

The circuit concept described above was first simulated in circuit simulation software (LTSpice), then implemented and tested. The simulations cover unequal current ratios as well as extension to multiple branches. The implementation was carried out for equal current ratios and two branches.

The circuit was tested both in the simulation and in practice by bridging a single LED D1 in one branch 20 and in the other branch. Without the current control circuit 30 according to the invention, the resulting asymmetry of the total flow voltages of the LED strings would lead to very different currents in the two current branches 20 . Table 1 below uses a measurement protocol to show the effect of the current control circuit 30 according to the invention in accordance with the first exemplary embodiment, which is shown in 1 shown and explained above. Table 1: Measurement results on the circuit implementation total current I(R1) [mA] 200 600 1000 1400 1800 symmetrical (no LED bridged) Supply voltage V1-V4 [V] 30.86 34.40 36:10 37.30 38.20 Working current left branch I(R2) [mA] 102.3 303 504 705 907 Working current right branch I(R2) [mA] 101.9 303 504 705 907 Leakage voltage left branch V2-V3 [V] 0.047 0.055 0.114 0.213 0.440 Leakage voltage right branch V2-V3 [V] 0.017 0.055 0.076 0.193 0.389 asymmetrical (one LED bridged) Supply voltage V1-V4 [V] 30.86 34.40 36:10 37.30 38.20 Working current left branch I(R2) [mA] 103.0 304 505 706 908 Working current right branch I(R2) [mA] 102.0 303 504 705 907 Leakage voltage left branch V2-V3 [V] 2,836 2,974 3.103 3,242 3,388 Leakage voltage right branch V2-V3 [V] 0.017 0.055 0.104 0.153 0.209

Table 1 shows that the current control circuit 30 compensates almost 100% for the asymmetry provoked by bridging an LED. This is a very safe estimate of the reliability of the current control, because in practical application it is more about the compensation of different forward voltages of individual light-emitting diodes D1, which have a much less drastic effect overall than bridging a light-emitting diode D1.

While the above embodiments and the simulations and test circuits are designed for a 1:1 split, the application of the present invention is not limited to equal current ratio splitting. For division into unequal currents, only the ratio of the load resistances R2 must be selected accordingly. This ratio can also be varied by means of different control resistors R4.

The capacitor C1 can be chosen to optimize the dynamic properties in the practical circuit.

• - eine automatische Stromteilung;
• - eine Verbesserung der Genauigkeit (<5% Abweichung);
• - eine Verbesserung der Robustheit gegenüber Stromstärke und Schaltungselement-Toleranzen;
• - ein gutes dynamisches Verhalten beim Ein- und Ausschalten, sowie im Pulsbetrieb;
• - ein einfacher Aufbau durch eine geringe Anzahl von Schaltungselementen;
• - die Möglichkeit einer Wiederverwertung des gleichen LED-Ketten-Aufbaus wie in den bisherigen Beleuchtungen, sowie einer Wiederverwertung der gleichen Leistungstransistoren;
• - eine hohe Effizienz aufgrund geringer Verlustleistung der Regelschaltung

erzielt werden. Die Schaltung hat des Weiteren den Vorteil, dass sie sich auch über einen weiten Bereich an ungleiche Stromteilungsverhältnisse anpassen kann, sowie auf mehrere (also zwei oder mehr) LED-Ketten-Zweige erweitert werden kann.According to the simulation and test results

• - an automatic current division;
• - an improvement in accuracy (<5% deviation);
• - an improvement in robustness to current and circuit element tolerances;
• - Good dynamic behavior when switching on and off, as well as in pulsed mode;
• - A simple structure with a small number of circuit elements;
• - the possibility of recycling the same LED chain structure as in the previous lighting, as well as recycling the same power transistors;
• - High efficiency due to low power loss of the control circuit

be achieved. The circuit also has the advantage that it can also adapt to unequal current sharing ratios over a wide range and can be extended to several (i.e. two or more) LED chain branches.

The exemplary embodiments explained above have a current source P1 which generates current pulses with different durations (1 μs -1 s) and with different current strengths (0.1 nA - 2A). The invention can also be operated with a current or voltage source with a constant output voltage or with a constant current signal.

Even short pulses can be safely and reliably regulated in the desired ratio with the current control circuit according to the invention. The current control circuit according to the invention thus shows a very fast response.

In the exemplary embodiments explained above, the power transistors T1 are in the form of normally-off field-effect transistors. Within the scope of the invention, normally on transistors can also be used, in which case the potential V4 present at the gate electrode should then be correspondingly inverted. In the case of self-conducting field-effect transistors, it can be expedient first to apply a blocking potential to them when the entire current control circuit is switched on, before the regulation by the current control circuit becomes effective.

The present invention has been described on the basis of several exemplary embodiments, which relate to the distribution of a supply current to two or more parallel current branches 20 with respective consumer networks 40, each of the consumer networks 40 being constructed by way of example as an LED chain with a large number of light-emitting diodes D1 connected in series . The current control circuit described However, 30 can also be applied to other types of consumer networks 40 connected in parallel, in which it is desired or necessary to maintain a specific current division ratio as precisely as possible. Non-linear loads can be used and a predetermined distribution is still achieved.

If there are more than two current branches 20, it is also conceivable to select a nested arrangement in which two or three current branches are combined and controlled in parallel and several such parallel circuits are combined and controlled to form an overall parallel circuit, instead of connecting all current branches 20 in parallel and closing them Taxes. In other words, each of the parallel circuits is understood as a consumer network. In this way, a two-stage or multi-stage control can be carried out, which may require a more complex circuit structure and more circuit elements, but may have advantages in terms of control technology.

Within the scope of this application, the term control is used throughout. In the context of this application, this term does not differentiate between simple forward control and regulation with feedback of the controlled variable.

It should also be pointed out that the qualitative designation of circuit elements such as resistors as ballast resistors, working resistors, scaling resistors, control resistors, equalizing resistors, diodes as control diodes, capacitors as equalizing capacitors, transistors as control or power transistors only indicates the functional assignment within the Circuit arrangements is used and does not have to mean any restriction with regard to the type, type and dimensioning of these circuit elements, unless this is expressly mentioned in the context.

Reference List

10

supply circuit

20

power branch

30

power control circuit

40

consumer network

50

control branch

60

terminal block

100

circuit arrangement

200

circuit arrangement

300

circuit arrangement

b

Base

c

collector

i.e

drainage

e

emitter

G

Gate

s

Source

C1

compensation capacitor

D1

light emitting diode (LED)

D2

control diode

D3

zener diode

P1

power source

R1

series resistor

R2

working resistance

R3

scaling resistance

R4

control resistor

R5

balancing resistance

T1

Power transistor (field effect transistor, nspecial MOSFET)

T2

Control transistor (bipolar transistor npn or pnp)

U1

Voltage drop across an LED

U2

Working voltage (voltage drop across working resistor R2)

V0

zero potential

V1

main supply potential

v2

consumer potential

V3

work potential

V4

current sink potential

V5

gate potential

V6

control main potential

V7

base potential

V8

reference work potential

Claims (18)

Current control circuit (30) for distributing a current from a common current source (P1) to a plurality of parallel consumer networks (40) with a predetermined current division ratio, the current control circuit (30) for each of the consumer networks (40) having: a power transistor (T1), in particular a field effect transistor, preferably a MOSFET, in series with the consumer network (40); a working resistor (R2) in series with the power transistor (T1) on its side remote from the load network (40), a working potential (V3) being defined between the working resistor (R2) and the power transistor (T1); a control resistor (R4), one side of which is connected to a control reference potential (V6) which is uniform for the entire current control circuit (30); a control transistor (T2), in particular a bipolar transistor, which is connected in a current path formed between the working potential (V3) and the other side of the control resistor (R4) which is remote from the control reference potential (V6), wherein the control electrode, in particular base (b), of the control transistor (T2) is connected to the control electrodes, in particular bases, of the control transistors (T2) of all other consumer networks (40) in order to form a base potential (V7) common to all control transistors (T2), coupled to the current paths between the control transistor (T2) and the control resistor (R4); and wherein a control electrode of the power transistor (T1) is connected to the current path between the control transistor (T2) and the control resistor (R4) provided for exactly one other of the load networks (40). Current control circuit (30) according to claim 1 , characterized in that the coupling of the common base potential (V7) is formed in each case by means of a control diode (D2) between the current path between the control transistor (T2) and the control resistor (R4) and the base potential (V7). Current control circuit (30) according to claim 2 , characterized in that the control diodes (D2) of all current branches are connected to one another and form a reference working potential (V8) which is connected to the base potential (V7) by means of a compensating resistor (R5). Current control circuit (30) according to any one of Claims 1 until 3 , characterized in that the current control circuit (30) has a zener diode (D3) which is connected between the control reference potential (V6) and a potential defined by the interconnected sides of the load resistors (R2) remote from the respective power transistor (T1). Current control circuit (30) according to claim 3 or 4 , characterized in that the control transistor (T2) is an npn transistor, the load networks (40) being provided on the side of a common main supply potential (V1) supplied by the current source (P1), the load resistors (R2) having a common current sink potential (V4), with respect to each of the consumer networks (40) in each case the working potential (V3) is a source potential of the power transistor (T1) and is connected to an emitter (e) of the control transistor (T2), the control electrode of one power transistor (T1) assigned to the consumer network (40) is connected to the collector (c) of the control transistor (T2) assigned to another consumer network (40), the control resistor (R4) is connected to the collector (c) of the control transistor (T2) which Control reference potential (V6) is connected to the main supply potential (V1) via a scaling resistor (R3), and the flow direction of the control diode (D2) to the Reference working potential (V8) indicates, and wherein the flow direction of the zener diode (D3) from the current sink potential (V4) to the control reference potential (V6) has. Current control circuit (30) according to claim 3 or 4 , characterized in that the control transistor (T2) is a pnp transistor, the load resistors (R2) being connected to a common main supply potential (V1) supplied by the current source (P1), the consumer networks (40) on the side of a common Current sink potential (V4) are provided, with respect to each of the consumer networks (40) in each case the working potential (V3) is a source potential of the power transistor (T1) and is connected to an emitter (e) of the control transistor (T2), the control electrode of one power transistor (T1) assigned to the consumer network (40) is connected to the collector (c) of the control transistor (T2) assigned to another consumer network (40), the control resistor (R4) is connected to the collector (c) of the control transistor (T2) which Control reference potential (V6) is connected to the current sink potential (V4) via a scaling resistor (R3), and the flow direction of the control diode (D2) depends on the Refe enzarbeitspotential (V8) points away, and wherein the flow direction of the zener diode (D3) from the main supply potential (V1) to the control reference potential (V6) has. Current control circuit (30) according to any one of the preceding claims 3 , 5 or 6 , characterized in that the compensating resistor (R5) is connected in parallel with a compensating capacitor (C1). A power control circuit (30) according to any one of the preceding claims, characterized in that the power source (P1) is a direct current source. Current control circuit (30) according to any one of Claims 1 until 7 , characterized in that the current source (P1) is a pulsed current source (P1). Current control circuit (30) according to one of the preceding claims, characterized in that the load resistors (R2) are fixed resistors. Current control circuit (30) according to any one of Claims 1 until 9 , characterized in that the working resistors (R2) are adjustable resistors. Current control circuit (30) according to one of the preceding claims, characterized in that the load resistors (R2) have a resistance ratio to one another which is selected in accordance with the predetermined current division ratio. A current control circuit (30) as claimed in any preceding claim, characterized in that the predetermined current sharing ratio is an equal current sharing ratio. Current control circuit (30) according to any one of Claims 1 until 12 , characterized in that the predetermined flow sharing ratio is a non-uniform flow sharing ratio. Current control circuit (30) according to one of the preceding claims, characterized in that a supply voltage resulting from a difference between the main supply potential (V1) and the current sink potential (V4) is less than or equal to a predetermined limit value, the predetermined limit value in particular is 48V. Circuit arrangement (100; 200; 300) with a multiplicity of parallel load networks (40), each of which has a multiplicity of series-connected light-emitting diodes (D1), and with a current control circuit (30) for distributing a current from a common current source (P1 ) to the plurality of parallel consumer networks (40) with a predetermined current division ratio, wherein the current control circuit (30) is constructed according to one of the preceding claims. Circuit arrangement (100; 200; 300) according to Claim 16 , characterized in that the consumer networks (40) are constructed identically, in particular with an identical number of light-emitting diodes (D1) of the same type. Circuit arrangement (100; 200; 300) with a multiplicity of parallel load networks (40) and with a current control circuit (30) for distributing a current from a common power source (P1) to the multiplicity of parallel load networks (40) with a predetermined current division ratio, wherein the current control circuit (30) according to any one of the preceding Claims 1 until 15 is constructed and each of the consumer networks has a non-linear consumer, in particular a light-emitting diode.

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