WO2011141207A1

WO2011141207A1 - Circuit and operation of a lighting unit, as well as a light having a circuit such as this

Info

Publication number: WO2011141207A1
Application number: PCT/EP2011/054204
Authority: WO
Inventors: Bernd Rudolph
Original assignee: Osram Gesellschaft mit beschränkter Haftung
Priority date: 2010-05-10
Filing date: 2011-03-21
Publication date: 2011-11-17
Also published as: DE102010028795A1

Abstract

A circuit is specified for operation of a lighting unit, comprising a balanced circuit (Q2, Q3) which can be biased via a reference voltage source (110), with the balanced circuit (Q2, Q3) being connected to a controlled system (Q1) with the aid of which it is possible to adjust a current from a power source (120) to the lighting unit (130). Furthermore, a light is proposed which has a circuit such as this.

Description

description

Circuit for operating a light unit and luminaire with such a circuit

The invention relates to a circuit for operating a lighting unit and a lamp with such

Circuit. Conventional LED torches often use only a resistive resistor to adjust the LED current.

If the nominal supply voltage is not significantly higher than the LED voltage, there is a strong dependence of the LED current and thus the brightness of the LED

Supply voltage. Thus, the state of the affects

Battery or the accumulator clearly noticeable on the brightness of the LED flashlight. This results in a user having the batteries early

exchanges. Thus, the capacity of the chemical cell is rarely exploited until the possible lower voltage.

There are also known electronic constant current sources that use special circuits and a

need relatively high supply voltage for operation. This results in significant losses, for example, shorten the battery life of the flashlight accordingly.

The object of the invention is to avoid the disadvantages mentioned above and in particular one

Possibility for a simple (linear) constant current source to provide, for example, to operate a

Flashlight or light unit with at least one semiconductor element. This object is achieved according to the features of the independent claims. Further developments of the invention will become apparent from the dependent claims. To achieve the object, a circuit for operating a light unit is specified,

comprising a current mirror, which has a

Bias voltage source is biased,

- Where the current mirror with a controlled system

connected by means of which a stream of one

Energy source to the light unit is adjustable.

The power source may include at least one (rechargeable) battery.

The proposed solution has the advantage that the electrical energy stored in a battery is used efficiently. The constant current source proposed here can be operated with a small voltage drop and has a good constant current characteristic.

A further development is that the lighting unit

comprises at least one semiconductor element.

Another development is that the controlled system is connected in series with the lighting unit. In particular, it is a continuing education that one

Current measuring resistor is connected in series with the controlled system and the lighting unit, wherein the current measuring resistor is connected to the current mirror. Also, it is a continuing education that parallel to the

Series circuit of current measuring resistor, controlled system and lighting unit, the energy source is arranged. Furthermore, it is a development that the current mirror has two bipolar transistors, wherein the

Bipolar transistors via their base terminals with each other and with the collector terminal one of

Bipolar transistors are connected.

In the context of an additional development of a bipolar transistor of the current mirror is arranged in base circuit, wherein the of the current measuring resistor

detectable current can be coupled as a voltage drop to the emitter of this bipolar transistor. The other

Bipolar transistor of the current mirror is arranged in emitter circuit and connected to its collector with the controlled system, in particular an input of the controlled system.

A next development is that a switch between the controlled system and the power source is arranged.

In particular, the switch can disconnect the controlled system from the energy source. For example, the switch can be connected directly, via one or more resistors to the base of the transistor, which can be used as a controlled system. If the switch is opened, the transistor blocks, the circuit is inactive.

An embodiment is that the controlled system comprises a transistor.

In particular, the controlled system may be a bipolar transistor, e.g. a pnp transistor, act. Also, the transistors mentioned here may be replaced by others

Transistors (e.g., field effect transistors) or

electronic components for switching or amplifying

electrical signals are replaced. An alternative embodiment is that the base of the transistor is connected as a controlled system to the current mirror. Thus, the transistor allows a controlled system and is biased over from the reference voltage

Current mirror activated.

A next embodiment is that the transistor is a bipolar transistor with low collector-emitter saturation voltage.

Such a low saturation bipolar transistor is also referred to as a "low saturation" bipolar transistor.

Also it is an embodiment that the

Reference voltage source provides a reference voltage which can be generated by the power source. A further development consists in that a diode, e.g. a zener diode and / or a light emitting diode, and / or a band-gap reference for adjusting the reference voltage is provided. An additional embodiment is that the

Current mirror has two pnp transistors and in which the controlled system comprises a pnp transistor.

The above object is also achieved by a luminaire comprising the circuit as described herein.

The lamp may be a flashlight or a flashlight. Embodiments of the invention are illustrated and explained below with reference to the drawing. It shows:

Fig.l is a schematic diagram of an LED linear constant current source.

Fig.l shows a schematic diagram of an LED linear constant current source. For example, such a circuit can be used in a mobile luminaire, e.g. a flashlight, are used.

A reference voltage source 110 provides a DC voltage Vref of, for example, 2.5V, and is connected to a node 101 through its positive pole and to a node 102 by its negative pole.

The reference voltage source 110 may be connected by means of a diode, e.g. a light emitting diode, a zener diode or a band gap reference can be set. The node 101 is further connected via a resistor R3 to the emitter of a pnp transistor Q2. The base of the transistor Q2 is connected to the base as well as to the

Collector of a pnp transistor Q3 connected. Furthermore, the collector of the transistor Q3 is connected to the node 102 via a resistor R4. The two transistors Q2 and Q3 represent a current mirror.

The collector of the transistor Q2 is connected to the base of a pnp transistor Ql, the base of the

Transistor Ql is still connected via a resistor R5 to the node 102.

The node 101 is connected via a resistor Rl both to the emitter of the transistor Q3 and to the emitter of the transistor Ql. The collector of the transistor Ql is connected to the negative pole of a battery 120 via a lighting unit 130 comprising a light-emitting diode D5. The Cathode of the LEDs D5 points in the direction of the negative pole of the battery 120. The positive pole of the battery 120 is connected to the node 101. The battery provides a voltage equal to Vbat (eg 4.5 volts). Instead of the light-emitting diode D5, a plurality of light-emitting diodes, for example in series, may be provided as lighting unit 130.

The lighting unit 130 may include at least one

Semiconductor lighting element include. For example, a white light-emitting diode (LED) can be used as the semiconductor light-emitting element.

The node 102 is connected through a resistor R6 and a

Switch Sl with the negative pole of the battery 120th

(Ground potential) connected. The switch Sl can also be implemented as an electronic switch (for example, as a transistor, a mosfet, an IGBT, etc.), so that by means of a known pulse width modulation (PWM) a

Brightness control (dimming) of the lighting unit 130 can be achieved.

If the switch S1 is closed, the lighting unit 130 via the battery 120 with electrical energy

supplied, wherein the current is adjusted by the lighting unit 130 by means of the transistor Ql so that a voltage drop of the battery voltage Vbat is compensated as long as possible.

The components shown in Fig.l can be as follows

be dimensioned: R1 = 1Q, R3 = 100Q, R4 = 2.2kQ, R5 = lkQ,

R6 = 0,5kQ. The light emitting diode D5 may be a Golden Dragon type white LED, the transistors Q2 and Q3 may be a BCV62, and the transistor Q1 may be a PBSS5250X type.

The current mirror comprising the transistors Q2 and Q3 is connected via the resistor R3 via the emitter of the transistor Q2 is set to a reference potential Vref. Of the

Resistor Rl serves as a current sensing resistor (shunt) at the emitter of transistor Q3. The collector current is

U B.E

Ic = Is (T, U _C E) · exp where

Ic the collector current,

I s a reverse current,

T the temperature,

U _CE a collector-emitter voltage,

Practice a base-emitter voltage,

U _{T is} a temperature voltage

describe

The temperature voltage U _T is about 26mV at 23 ° C. The current mirror comprises the transistors Q2, Q3, for example in the form of a double transistor with almost identical reverse current I s and almost identical collector current I _c . Thus follows for the ratio of the collector currents of the two

Transistors Q2 and Q3:

U BE.Q2

exp

^L C, Q2 u TUB, E, Q2

exp u B, E.Q3

U BE, Q3

exp u T

ur

The transistor Ql realizes a controlled system and wi over the biased from the reference voltage Vref

Current mirror controlled.

In particular, a so-called low-saturation bipolar transistor Q1 is used as the transistor Ql, which up to very small voltage drops (eg 100mV) over its emitter-collector path is operable.

The LED current is measured via the resistor Rl (shunt resistor) in the emitter circuit of the transistor Ql and operated on the base circuit as well as the

Reference voltage source Vref biased transistor Q3 coupled to the bipolar current mirror. The other

Transistor Q2 of the current mirror is arranged in emitter circuit and with its collector to the base of

Transistor Ql connected. This will close the loop.

In active operation of the circuit (ie, when switch S1 is closed), a distribution of the supplied current takes place at a node 103 in such a way that a part flows off through the transistor Q2 and another part is supplied to the transistor Q1. By the proposed dimensioning of the resistors Rl, R3 and R5 of the current mirror is achieved that a decreasing current through the light emitting diode D5 is approximately proportional to the current through the

Resistor R3. This increases with decreasing current

Current, which is passed via the node 103 to the base of the transistor Ql to. Thus, a decrease in power of the battery 120 can be at least temporarily compensated, without this leading to a strong loss of brightness of the lighting unit 130.

Preferably, the switch Sl serves to turn on and off the whole system with low power consumption without having to disconnect the battery. Nevertheless, it is

ensures that no power is consumed when switch S1 is open. For example, at a supply voltage Vbat in a range of 0V to 5V even at a low voltage drop across the resistor Rl and the transistor Ql in the amount of 280mV an LED current of about 142mA (this already corresponds to about 97.5% of the maximum at the SV supply voltage) can be achieved. With this cost-effective circuit, a very good current constancy of the LED with minimal voltage drop, so up to very small battery voltages possible. As a result, the battery is used efficiently, as long as possible, a nearly constant brightness of the LED is guaranteed.

It should be noted that the circuit shown in Fig.l can also be constructed according to npn transistors (dual).

List of reference numbers:

101 knots

102 knots

103 knots

110 reference voltage source

120 battery (power supply)

130 light unit

Ri resistance

Qi pnp transistor

Sl switch

Vref reference voltage

Vbat battery voltage

Claims

claims

1. Circuit for operating a lighting unit (130),

- comprising a current mirror (Q2, Q3), over

a reference voltage source (110) can be prestressed,

- wherein the current mirror (Q2, Q3) with a

Controlled system (Ql) is connected, by means of which a current from an energy source (120) to the

Light unit (130) is adjustable.

2. A circuit according to claim 1, wherein the lighting unit (130) comprises at least one semiconductor element (D5). 3. A circuit according to any one of the preceding claims, wherein a current measuring resistor (Rl) in series with the controlled system (Ql) and the lighting unit (130)

is connected, wherein the current measuring resistor (Rl) is connected to the current mirror (Q3).

Circuit according to Claim 3, in which the energy source (120) is arranged parallel to the series connection of current measuring resistor, controlled system and lighting unit.

A circuit according to any one of claims 3 or 4, wherein the current mirror comprises two bipolar transistors (Q2, Q3), the base terminals of the

Bipolar transistors with each other and with the

Collector terminal of one of the bipolar transistors (Q3) are connected.

Circuit according to Claim 5,

- In which a bipolar transistor (Q3) of the

Current mirror is arranged in base circuit, wherein the of the current measuring resistor (Rl) detectable current on the emitter of this

Bipolar transistor (Q3) can be coupled,

in which the other bipolar transistor (Q2) of the

Current mirror arranged in emitter circuit and connected to its collector with the controlled system (Ql).

Circuit according to one of the preceding claims, in which a switch (S1) is arranged between the controlled system (Q2) and the energy source (120).

Circuit according to one of the preceding claims, in which the controlled system comprises a transistor (Ql).

A circuit according to any one of the preceding claims, wherein the reference voltage source provides a reference voltage which is producible by the power source.

A circuit according to claim 9, wherein a band-gap reference is for adjusting the reference voltage

is provided.

A circuit according to claim 9, wherein a diode,

in particular a zener diode or a light emitting diode, is provided for setting the reference voltage.

Circuit according to one of the preceding claims be the current mirror has two pnp transistors and wherein the controlled system comprises a pnp transistor.

13. Luminaire comprising the circuit according to one of

previous claims.