Driver circuit for an optoelectronic sensor

Abstract

Driver circuit (3) for supplying a light-emitting unit (5) of an optoelectronic sensor with a transmission current, wherein the driver circuit (3) comprises a voltage supply (7) for supplying the light-emitting unit (5). The driver circuit (3) comprises a first driver (3a) and a second driver (3b) connected in parallel, wherein the first driver (3a) has a first switching input (13a) and the second driver (3b) has a second switching input (13b) for switching the transmission current, wherein the first driver (3a) and the second driver (3b) each comprise a first transistor (Q1a, Q1b) and a second transistor (Q2a, Q2b);wherein the first transistors (Q1a, Q1b) are designed as PNP transistors and the second transistors (Q2a, Q2b) are each designed as NPN transistors, and the emitter of the first transistor (Q1a, Q1b) is each connected to the base of the second transistor (Q2a, Q2b), or wherein the first transistors (Q1a, Q1b) are designed as NPN transistors and the second transistors (Q2a, Q2b) are each designed as PNP transistors and the emitter of the first transistor (Q1a, Q1b) is each connected to the base of the second transistor (Q2a, Q2b); and wherein the two drivers (3a, 3b) are connected to a common control input (11) for controlling or regulating an amplitude of the transmission current, wherein the two drivers (3a, 3b) are further connected to a common driver output (9) which is connectable to the light transmission unit (5), wherein the first driver (3a) and the second driver (3b) have different operating ranges.;

Description

[0001] The invention relates to a driver circuit for an optoelectronic sensor, as well as a circuit with a driver circuit.

[0002] Optoelectronic sensors, such as proximity switches, rangefinders, or line scanners, have long been known and are also manufactured and sold by the applicant in large quantities. They usually have a pulsed light emitting unit, usually one or more light-emitting diodes (LEDs) or laser diodes. Depending on the type of light emitting unit, a customized circuit, in particular a customized driver with a corresponding operating range, must be used, which has a negative impact on manufacturing costs. Typical transmission currents for operating the light emitting unit have currents in the range of several tens of milliamperes in the case of laser diodes and in the range of several hundred milliamperes in the case of light-emitting diodes. Furthermore, it is often advantageous if the amplitude of the transmission current can be varied.This is particularly desirable when implementing automatic power correction or when avoiding receiver overloads with highly reflective or specular objects. Other reasons include compensating for temperature fluctuations and the decreasing efficiency of the aforementioned transmitting components over time. However, a large operating range, which allows for large amplitude variations, can have a negative impact on the adjustment resolution of the amplitude control. Typical pulse lengths are in the range of a few microseconds.

[0003] DE 195 46 562 C1 shows a circuit with a power FET. The disadvantage of this circuit is that the pulse length can be varied, but not the pulse height (amplitude).

[0004] WO 2010 / 117500 A2 discloses a current source for driving a light source in an optical sensor system. The current source is configured to receive a regulated DC voltage and provide a current to the light source via an inductor when a switch is closed, and to conduct current through the inductor when the switch is open.

[0005] EP 2 123 124 B1 discloses an electronic device for driving at least a first channel and a second channel of light-emitting diodes, wherein a driver means having a first driver part and a driver means having a second driver part are provided for separately driving the first and the second channel of light-emitting diodes.

[0006] The object of the invention is to provide a driver circuit and a circuit with a driver circuit for an optoelectronic sensor, which can be operated with different light emitting units, enables a large variation of the amplitude of the transmitting current and a precise control of the transmitting current for controlling a light emitting unit of an optoelectronic sensor, and which can be implemented simply and cost-effectively.

[0007] The object is achieved by a driver circuit according to claim 1. Advantageous embodiments of the invention, in particular also a circuit with a driver circuit, are specified in the dependent claims.

[0008] Advantageously, a driver circuit is provided for supplying a light-emitting unit of an optoelectronic sensor with a transmission current, wherein the driver circuit comprises a voltage supply for supplying the light-emitting unit. The driver circuit comprises a first driver and a second driver connected in parallel, wherein the first driver has a first switching input and the second driver has a second switching input for switching the transmission current. The first driver and the second driver each comprise a first transistor and a second transistor.wherein the first transistors are PNP transistors and the second transistors are each NPN transistors, and the emitter of the first transistor is connected to the base of the second transistor, or wherein the first transistors are NPN transistors and the second transistors are each PNP transistors, and the emitter of the first transistor is connected to the base of the second transistor; and wherein the two drivers are connected to a common control input for controlling or regulating an amplitude of the transmission current, wherein the two drivers are further connected to a common driver output that can be connected to the light transmission unit, and wherein the first driver and the second driver have different operating ranges.

[0009] The driver circuit thus makes it possible to provide different operating ranges for controlling the light emitting unit. Since both drivers share a common control input, a fine amplitude adjustment (with high adjustment resolution) of the transmitted current can be made in each of the operating ranges. The adjustment resolution can, for example, correspond to a minimal variation in the light emitting unit's light output of 0.1% to 5%.

[0010] The first driver can, in particular, have a first operating range that allows a maximum transmission current in a first current range, while the second driver can have a second operating range that allows a maximum transmission current in a second current range. In particular, it can be provided that the first current range and the second current range do not overlap. In a first example, the first current range can be selected to be in the range from 5 mA to 25 mA, and the second current range can be selected to be in the range from 25 mA to 125 mA. This allows, in particular, the dynamic range of an LED to be adapted.

[0011] In another example, the first current range can be selected to be in the range from 20 mA to 100 mA, and the second current range can be selected to be in the range from 80 mA to 400 mA. This makes it possible, in particular, to provide a driver circuit that is suitable for driving both an LED and a laser diode.

[0012] Preferably, the control input comprises a parallel circuit of a capacitor and an adjustable resistor.

[0013] The first transistors can each be designed as bipolar transistors, with the control input connected to a base of the first transistor. Likewise, the second transistors can advantageously be designed as bipolar transistors.

[0014] To adjust the operating ranges, the first driver and the second driver can have different component specifications. In particular, a resistor through which the transmit current flows, which is connected, for example, between the second transistor and a reference potential (e.g., ground), can be selected differently. In general, the resistors and capacitors can be adapted to the respective operating range. Similar transistors can advantageously be designed as double transistors.

[0015] Furthermore, the invention relates to a circuit with the aforementioned driver circuit, wherein the circuit comprises a first switching signal source and a second switching signal source. The first switching signal source is connected to the first switching input, and the second switching signal source is connected to the second switching signal input. Furthermore, the circuit can comprise an analog control signal source connected to the control input.

[0016] Preferably, the first switching signal source and the second switching signal source are each embodied as a pulse signal source and / or a digital switching signal source. A corresponding switching signal can, for example, have a high level and a low level and be modulated at a high frequency. The pulse signal can, for example, have a low level of 0 V and a high level with a voltage magnitude of up to 6 V.

[0017] The control signal source can preferably be configured to output an analog control signal. For example, the control signal source can comprise a digital-to-analog converter (DAC). For example, if a 12-bit DAC is used that outputs a variable voltage signal, the voltage signal can be varied in up to 4096 steps. For example, the variable voltage signal can have a magnitude in the range of 0.2 V to 6 V.

[0018] In some embodiments of the circuit, it is provided that it receives a pulse signal from the switching signal source and outputs a pulsed transmission current. The second transistor can then serve to transmit the pulse signal, and the first transistor can serve to transmit a control signal provided by the switching signal source for amplitude control. In particular, the emitter of the first transistor can be connected to a negative feedback resistor and to the base of the second transistor. Furthermore, the collector of the first transistor can be connected to a reference potential. The emitter of the second transistor can be connected to the reference potential via a resistor.

[0019] The circuit has the advantage that a temperature-stable and cost-effective circuit can be provided, which places little load on the amplitude source.

[0020] A particular advantage of the circuit is that the first switching input and the second switching input are designed separately from the control input. For example, the switching signal sources and the control signal source can be integrated into a microcontroller (µC) or an ASIC. The transistors can each be designed as a bipolar transistor. For example, a circuit board can be equipped with a corresponding µC, wherein the µC comprises two or four bipolar transistors, as well as an analog control output and two digital switching outputs. The circuit board can then be equipped with an additional capacitor, an additional resistor per driver, and optionally two additional bipolar transistors. This allows the circuit to be manufactured cost-effectively.

[0021] In a further aspect, an optoelectronic sensor is specified with a light-emitting unit and with the aforementioned circuit or driver circuit. In particular, the optoelectronic sensor can be a proximity switch. The optoelectronic sensor can also, in particular, have a photodetector, for example a charge-coupled device (CCD) or a time-of-flight sensor, in particular a photonic mixer detector (PMD). The optoelectronic sensor can thus be equipped and operated with at least one LED or with at least one laser diode as the light-emitting unit.

[0022] In some embodiments, the optoelectronic sensor includes a circuit section for automatic power correction (APC). An actuator output of the APC can then be connected to the control signal input. This can be particularly advantageous for operating designs with one or more laser diodes as the light-emitting unit.

[0023] A method for operating an optoelectronic sensor with a light-emitting unit and with a driver circuit is also specified, wherein the driver circuit comprises a voltage supply for supplying the light-emitting unit, as well as a first driver and a second driver connected in parallel thereto; wherein the method provides for selecting or defining an operating range for controlling the light-emitting unit and controlling the light-emitting unit by means of the first driver or the second driver depending on the operating range.

[0024] Advantageously, the first driver comprises a first switching input and the second driver a second switching input, wherein the two drivers are connected to a common control input for controlling a transmission current of the light transmission unit. The light transmission unit can then be operated within the scope of the method by sending a switching signal to the first switching signal input or to the second switching signal input. The amplitude of the transmission current can be controlled via the common control input. In particular, the control input can be controlled using an analog voltage signal for control. Since a common control input is used, a maximum number of control steps, which is specified, for example, by a DAC, can be provided for each of the operating ranges. This enables fine control over a wide range of the transmission current.

[0025] Advantageously, the optoelectronic sensor can also comprise a photodetector. The method can then provide for selecting or defining the operating range of the driver circuit as a function of the sensor signal strength of the photodetector. For example, the sensor signal strength of the photodetector is compared with an upper and a lower threshold. If the upper threshold is reached, the transmission current can be reduced by controlling the light-emitting unit via the driver whose operating range is designed for lower transmission currents. Conversely, if the lower threshold is reached, the transmission current can be increased, whereby the light-emitting unit is controlled via the driver whose operating range is designed for higher transmission currents. Thus, a switching signal can be sent either to the first switching signal input or to the second switching signal input to switch on the relevant driver 3a or 3b.

[0026] Furthermore, a method for producing an optoelectronic sensor with a light-emitting unit and with a circuit is specified, wherein the circuit comprises a voltage supply for supplying the light-emitting unit and a driver circuit with a first driver and a second driver connected in parallel thereto; wherein the method provides for selecting a light-emitting unit and equipping the optoelectronic sensor with it, defining an operating range for controlling the light-emitting unit depending on the selected light-emitting unit, and configuring or setting up the optoelectronic sensor depending on the selected operating range for using the first driver or the second driver.

[0027] The optoelectronic sensor can in particular be operated, and / or manufactured, or configured by means of one of the methods mentioned.

[0028] The invention is explained in more detail below using exemplary embodiments with reference to the drawings.

[0029] They show schematically: - Fig. 1 an exemplary embodiment of a circuit with a driver circuit for an optoelectronic sensor, with two parallel drivers; - Fig. 2 an exemplary further development of the circuit from Fig. 1; - Fig. 2a an exemplary further development of the circuit from Fig. 2, wherein the control signal input here comprises an adjustable resistor; - Fig. 3 an exemplary further training of a driver; - Fig. 4 an exemplary further training of a driver; - Fig. 5 an exemplary further training of a driver; - Fig. 6 is a flow chart relating to a method for manufacturing an optoelectronic sensor; and - Fig. 7 a flowchart relating to a method for operating an optoelectronic sensor.

[0030] In the following description of the preferred embodiments, like reference numerals designate like or comparable components.

[0031] The Fig. Figure 1 shows a circuit 1 with a driver circuit 3 for an optoelectronic sensor with a light emitting unit 5. The driver circuit 3 comprises a first driver 3a and a second driver 3b, with the two drivers 3a, 3b being connected in parallel and having different operating ranges. The light emitting unit 5 is connected to the driver circuit 3 via a driver output 9 on the one hand, and to a voltage source 9 on the other. In the example, the light emitting unit 5 is illustrated as a light-emitting diode (LED).

[0032] The driver circuit 3 further comprises a control input 111. Furthermore, the first driver 3a comprises a first switching input 13a, and the second driver 3b comprises a second switching input 13b.

[0033] A control signal source 111 of circuit 1 is connected to the control input 11. Furthermore, a first switching signal source 113a is connected to the first switching input 13a, and a second switching signal source 113b is connected to the second switching signal input 13b.

[0034] By means of the first switching signal source 113a and the second switching signal source 113b, the respective drivers 13a, 13b can be switched on and off, so that a transmission current flowing through the light transmission unit 5 is switched. The amplitude of the transmission current can be controlled and / or regulated by means of the control signal source 111. The control signal source 111 can, for example, comprise a digital-to-analog converter (DAC). In particular, it can be provided that the DAC is controlled by a microcontroller with a digital signal and outputs an analog signal to the control input 11. For example, a variable voltage in the range from 1V to 5V can be provided at the control input 11. Alternatively, the control input 11 can be connected to an actuator output of an APC.

[0035] In a first application, the circuit 1 can be used in an optoelectronic sensor, which, for example, has a light-emitting unit 5 designed as an LED. The first driver 3a has, for example, a first operating range that extends around a first operating point. Correspondingly, the second driver 3b has, for example, a second operating range that extends around a second operating point. For example, the operating ranges can be spaced apart from one another. To adjust the transmission current, and thus the emitted light power, either the first driver 3a can be switched on by means of the switching signal source 113a or the second driver 3b can be switched on by means of the second switching signal source 113b. In particular, a pulse signal for switching the transmission current on and off can be applied to the switching signal source.

[0036] The optoelectronic sensor can further comprise a photodetector. By adjusting the transmission power, the detected signal strength of the photodetector can also be influenced. If the photodetector reaches saturation, the driver 3a or 3b with a lower operating range can be switched on, for example. The number of control steps, which is limited, for example, by a DAC, remains constant in each of the operating ranges, allowing precise amplitude control over a wide amplitude range.

[0037] In the Fig. In the embodiment shown in Figure 2, the two drivers 3a, 3b each comprise a circuit with a first transistor Q1a, Q1b and a second transistor Q2a, Q2b. The first transistors Q1a, Q1b are each designed as PNP transistors and the second transistors Q2a, Q2b are each designed as NPN transistors, and the emitter of the first transistor is connected to the base of the second transistor. The base of the second transistor Q2a, Q2b then serves in a known manner as an input for a switching signal, for example a digital switching signal or pulse signal. The current signal generated at the collector of the second transistor Q2a, Q2b serves to supply the light emitting unit 5, e.g., an LED. The negative feedback resistor R1a, R1b, together with the collector-emitter path of the first transistor Q1a, Q1b, forms a voltage divider for adjusting the amplitude of the output signal.The base of the first transistor Q1a, Q1b serves as the amplitude input.

[0038] While the switching signal is at a high level, the emitter of the second transistor Q2a, Q2b has approximately the same potential as the control input (control signal source 111) supplied with a control voltage Vadj. Thus, a current I flowing through the resistor R2a R2a approximately to I R2a = Vadj / R2a, or a current I flowing through the resistor R2b R2b to I R2b = Vadj / R2b.

[0039] Since the base-emitter junctions of the first transistor Q1a, Q1b and the second transistor Q2a, Q2b are each connected in parallel, their temperature drift is compensated. Only minimal requirements are placed on the control signal source 111. The control signal source 111 can have a high internal resistance because it is subjected to only a small load. The control voltage Vadj provided by the control signal source 111 can always be present, even while both drivers 3a, 3b are switched off. Therefore, the control voltage Vadj can be generated by voltage dividers, pulse-width-modulated signals with low-pass filters, or D / A converters. Low-pass capacitors can be provided to reduce the radiation of high-frequency interference signals.

[0040] In the example, the second transistors Q2a and Q2b are each designed as NPN transistors and drive the transmit current through the light emitting unit. The first transistors Q1a and Q1b are designed as PNP transistors in the example and serve to control the amplitude of the transmit current.

[0041] The Fig. 2a essentially corresponds to the Fig. 2, however, the control signal source 111 here comprises a potentiometer Rvar, in particular an adjustable resistor. The potentiometer is connected between the light emitting unit 5 and ground GND, with an adjustment tap for adjusting the resistance value connected to a capacitor C and the control signal input 11.

[0042] The Fig. Figure 3 shows an exemplary further development of the first driver 3a. The second driver 3b can be designed analogously. In contrast to the Fig. 2, the light emitting unit 5 is grounded, which can be advantageous for its cooling or electrical shielding. The illustrated embodiment of the driver 3a functions in the manner described above. Only the control signals need to be inverted.

[0043] Fig. Figure 4 shows an example with signal sources 111 and 113a referenced to the operating voltage Ub. For clarity, only a further development of the first driver 3a is shown. The second driver 3b can be designed analogously.

[0044] Fig. 5 shows an embodiment of the first driver 3a with two control signal sources 111, which can be logically linked with OR. The second driver 3b can in turn be designed analogously and likewise connected to the two control signal sources 111. The smaller of the control voltages Vadj1 or Vadj2 generated by the two control signal sources 111 determines the current amplitude. This can be useful for controlling a light emitting unit 5 designed as a laser diode with a soft start ramp (Vadj1) and amplitude control (Vadj2). The control signals must be independent of one another, since the soft start function is a reaction to the switching on of the operating voltage, and the amplitude control is a reaction to the monitor diode current or light generation of the light emitting unit 5, e.g., a laser diode.

[0045] In some embodiments, the first driver 3a or the second driver 3b can be optimized for operating an LED, while the other driver 3a or 3b is optimized for operating a laser diode.

[0046] The Fig. 6 shows a flowchart illustrating a method for manufacturing an optoelectronic sensor. The optoelectronic sensor comprises a driver circuit 3 with two parallel drivers 3 and 3b. In a first step S1, a light-emitting unit 5 is selected to be installed in the optoelectronic sensor, and the circuit 1 is equipped with it. Depending on the selected light-emitting unit 5, an operating range for operating the light-emitting unit 5 is then defined in a step S3. In a subsequent step S5, the optoelectronic sensor is set up or configured to control the light-emitting unit 5 using the first driver 3a or the second driver 3b, depending on the selected operating range. This can be done, for example, by loading appropriate firmware onto a microcontroller and / or by transmitting configuration data.Thus, a method can be provided by which a circuit 1 with a driver circuit 3 can be provided for operating different types of light emitting units 5. In particular, the method makes it possible to operate light emitting units 5 configured as LEDs or laser diodes with the same circuit 1. This enables cost-effective production of the optoelectronic sensor.

[0047] A method for operating an optoelectronic sensor is described as a schematic flow diagram in the Fig.7. The method makes it possible to control and / or regulate a transmission current, and thus a light output of the optoelectronic sensor, over a wide range, whereby a small increment of control steps is enabled. In a step S11, an operating range for controlling the light transmission unit 5 can be selected. The light transmission unit 5 can then be operated by means of the first driver 3a or the second driver 3b, depending on the selected operating range. A corresponding switching signal for switching on the light transmission unit 5, for example a pulse signal, can therefore be sent to the first switching signal input 113a or the second switching signal input 113b. For example, this can be done depending on a detector signal output by a photodetector. The first driver 3a can, for example, be designed to control the light transmission unit 5 with a low current.Accordingly, the second driver 3b can be designed to drive the light-emitting unit with a low current. If the photodetector now reaches a saturation range while the light-emitting unit 5 is being operated via the second driver 3b, a switch can be made by sending corresponding signals to the switching signal inputs 113a, 113b of the drivers 3a, 3b. The light-emitting unit 5 can then continue to be operated with a low transmission current using the first driver 3a. Conversely, if the signal strength of the detector signal of the photodetector falls below a lower threshold while it is being operated by the first driver 3a, a switch can be made to operation using the second driver 3b, thus increasing the transmission current. In an optional method step S15, the amplitude of the transmission current can be controlled within the selected operating range via the common control input 13. List of reference symbols 1 circuit 3 Driver circuit 3a, 3b drivers 5 Light emitting unit 7 Voltage source 9 Drive exit 11 Control input 13a first switching signal input 13b second switching signal input 111 Control signal source 113a first switching signal source 113b second switching signal source C capacity GND ground connection Q1a, Q1b transistors Q2a, Q2b transistors R1a, R1b negative feedback resistors R2a, R2b resistors Rvar adjustable resistance S1, S3, S5 process steps S11, S13, S15 process steps

Claims

[1] Driver circuit (3) for supplying a light transmitting unit (5) of an optoelectronic sensor with a transmitting current, wherein the driver circuit (3) comprises a voltage supply (7) for supplying the light transmitting unit (5), wherein the driver circuit (3) comprises a first driver (3a) and a second driver (3b) connected in parallel thereto, wherein the first driver (3a) has a first switching input (13a) and the second driver (3b) has a second switching input (13b) for switching the transmission current, wherein the first driver (3a) and the second driver (3b) each comprise a first transistor (Q1a, Q1b) and a second transistor (Q2a, Q2b); wherein the first transistors (Q1a, Q1b) are designed as PNP transistors and the second transistors (Q2a, Q2b) are each designed as NPN transistors, and the emitter of the first transistor (Q1a, Q1b) is connected to the base of the second transistor (Q2a, Q2b), or wherein the first transistors (Q1a, Q1b) are designed as NPN transistors and the second transistors (Q2a, Q2b) are each designed as PNP transistors and the emitter of the first transistor (Q1a, Q1b) is connected to the base of the second transistor (Q2a, Q2b); and wherein the two drivers are connected to a common control input (11) for controlling or regulating an amplitude of the transmission current, wherein the two drivers (3a, 3b) are further connected to a common driver output (9) which can be connected to the light transmission unit (5), and wherein the first driver (3a) and the second driver (3b) have different operating ranges. [2] Driver circuit (3) according to claim 1, wherein the control input (11) comprises a parallel circuit of a capacitance and an adjustable resistor (Rvar). [3] Driver circuit (3) according to one of claims 1 or 2, wherein the first transistors (Q1a, Q1b) are each designed as bipolar transistors and wherein the control input (11) is each connected to a base of the first transistor (Q1a, Q1b). [4] Circuit (1) with a driver circuit (3) according to one of claims 1 to 3, wherein the circuit (1) comprises a first switching signal source (113a) and a second switching signal source (113b), wherein the first switching signal source (113a) is connected to the first switching signal input (13a) and the second switching signal source (113b) is connected to the second switching signal input (13b) and / or wherein the circuit (1) comprises an analog control signal source (111) which is connected to the control input (11). [5] Circuit (1) according to claim 4, wherein the first driver (3a) is designed to receive a pulse signal from the first switching signal source (113a) and the second driver (3b) is designed to receive a pulse signal from the second switching signal source (113b), wherein the drivers (3a, 3b) each output a pulsed current signal, wherein the second transistor (Q2a, Q2b) is used to transmit the pulse signal and the first transistor (Q1a, Q1b) is used to transmit a control signal provided by the control signal source (111) for controlling an amplitude of the transmission current, wherein the emitter of the first transistor (Q1a, Q1b) is connected to a negative feedback resistor (R1a, R1b), the emitter of the first transistor (Q1a, Q1b) is connected to the base of the second transistor (Q2a, Q2b), and the collector of the first transistor (Q1a, Q1b) is connected to the base of the second transistor (Q2a, Q2b). connected to a reference potential (GND), and the emitter of the second transistor (Q2a,Q2b) is each connected to the reference potential (GND) via a resistor (R2a, R2b).

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