CN111989833A

CN111989833A - Light source for generating light pulses with short pulse duration and method for generating short light pulses with a light source

Info

Publication number: CN111989833A
Application number: CN201980025895.5A
Authority: CN
Inventors: 安德烈·斯洛维奇
Original assignee: Elmers Semiconductor Europe
Current assignee: Elmers Semiconductor Europe
Priority date: 2018-04-16
Filing date: 2019-04-12
Publication date: 2020-11-24
Anticipated expiration: 2039-04-12
Also published as: WO2019201805A1; DE112019001975A5; DE102018108910B3

Abstract

A method of generating short pulses and a light source for generating light pulses with a short pulse duration, in particular for a vehicle, comprising a light-emitting diode (3) for generating light pulses and a push-pull circuit (2) for controlling and supplying the light-emitting diode (3), wherein the light-emitting diode (3) has a first connection (10) and a second connection (12) which are connected to an output port (20) of the push-pull circuit (2), the push-pull circuit (2) can be switched to a first state in which positive electrical energy of the first supply line (42) is present at the output port (20) of the push-pull circuit (2) and the light-emitting diode (3) emits electromagnetic radiation, and the push-pull circuit can be switched to a second state in which, the negative electric energy of the second power supply line (44) exists on the output port (20), and wherein a difference between a potential of a center potential line (14) on a second terminal (12) of the light emitting diode (3) and a potential of the first power supply line (42) is smaller than a difference between a potential of the center potential line (14) and a potential of the second power supply line (44).

Description

Light source for generating light pulses with short pulse duration and method for generating short light pulses with a light source

Technical Field

The invention relates to a light source for generating light pulses with short pulse durations in the nanosecond range, in particular for vehicles. The light source comprises a light emitting diode for generating a light pulse and a push-pull circuit for controlling and powering the light emitting diode. The invention also relates to a method for generating short light pulses by means of a light-emitting diode and a push-pull circuit.

Background

In the field of automotive technology, driver assistance is becoming increasingly important. Assistance ranges from driving assistance systems to automatic driving of vehicles. For this purpose, systems for optical distance and speed measurement are used. LIDAR (laser radar) systems (Light Detection and Ranging) play an important role in a process similar to that of radar measurement, but using a laser beam or other Light source. In the future, the LIDAR system will play a more important role in an improved driving Assistance system (Advanced Driver Assistance Systems, ADAS Advanced driving Assistance system) and automatic driving. The current stringent requirements on functional safety require a reliable and sensitive system in order to be able to make correct decisions in extreme cases. Therefore, in many application areas, these systems require very short light pulses. For this reason, expensive laser diodes are generally employed in order to achieve pulses with pulse durations of less than about 10 ns. A main application of such pulsed light sources is the time-of-flight measurement for distance determination, as used, for example, in the so-called Flash laser radar (Flash-LIDAR).

Since the measurement information is contained in the edge of the pulse, shortening the pulse length is equivalent to improving the efficiency. This can directly translate into an increase in performance. However, especially for LIDAR systems with a large detection range, the system performance is limited by the allowed transmit power of the light source. Therefore, an efficient light source is at least as important as a sensitive sensor for system performance.

Conventional LIDAR systems typically use a deflectable laser beam that is directed by a mirror. The laser used has the problem of high energy density in order to build a system with a large detection range. Lasers with high energy density may damage the eye and thus their optical power is limited by legal regulations.

Currently used for flash LIDAR systems are dedicated infrared pulse sources. These infrared pulse sources are limited in their detection range and sensitivity by the emission power that is legally limited to ensure eye safety.

Based on predetermined boundary conditions, pulsed light sources with short light pulses have an increased importance for time-of-flight measurements, which are necessary for distance or distance determination. The efficiency of the time-of-flight measurement also depends on the pulse length. A reduction in the pulse length increases the efficiency, since a larger detection range can be achieved with a constant average light power.

In the automotive field, LIDAR systems known in the art are typically manufactured with dedicated light sources. For reasons of acceptance, the light sources used are limited to the wavelength range of invisible light, while at the same time the small size requirements dictated by the available structural space in the vehicle must be met. Both of these limitations have a diminishing and degrading impact on the maximum transmit power and system performance in view of the radiation power limits set to avoid eye damage.

Therefore, there is a relatively large need to increase the effective range. This can be achieved in particular by means of a pulsed light source. It has been recognized within the scope of the present invention that a key issue lies in the generation of light pulses of a light emitting diode, LED (light emitting diode) or laser diode, which have steep edges, i.e. with steep rising edges and steep falling edges. The rising edge reflects the turning on of the diode and the falling edge reflects the turning off of the diode.

In the prior art, the LED pulses are generated by a switchable current or voltage source. The rise and fall times of the light pulses thus achieved are typically in the order of 10 ns. For conventional light emitting diodes and laser diodes, this limitation is caused by the heavy loading of the barrier capacitance together with the diode and its connected parasitic elements.

EP 0470780 a1 describes a device for improving the pulse shape, in particular the rising edge, of an LED. In which four bipolar transistors are interconnected in an H-bridge for operating light emitting diodes, LEDs. The disclosed circuit must have two resistors in the blocking direction in order to limit the cross current in the two H-bridges that occurs with use. Thereby limiting the turn-off behavior of the circuit. Furthermore, the proposed circuit has to comprise a current source, which requires the integration of at least one further current source transistor in the circuit. Thus, the circuit shown does not use voltage supply, but current supply by an existing current source. However, the additional current sources create additional space requirements on the chip when integrating the circuit into an integrated microelectronic circuit. The LED operates in an off state when the first high-side transistor of the first half-bridge is turned off, the second high-side transistor of the second half-bridge is turned off and at the same time the first low-side transistor of the first half-bridge is turned on, and the second low-side transistor of the second half-bridge is turned off. That is to say, the light-emitting diode is connected to the current source only by its anode via the first low-side transistor of the first half-bridge. This is shown in fig. 1 of EP 0470780 a 1. In this state, the cathode of the LED is not wired, and therefore, the LED is not connected to the energy source in the off state. In order to generate the shortest possible light pulse, shortly after the first high-side transistor and the two low-side transistors are switched on, this second high-side transistor is switched on with a delay time τ, and thus receives a portion of the current source. The LED is switched off only by the first low-side transistor. However, the "cancellation current" is limited by the current source. Only for times determined by current source t＝Q_LED/I_{Current source}＝C_LEDx U_LED/I_{Current source}To turn off the LED. In this case, the discharge process is also impeded by the resistance. This prolongs the discharge time. Although the circuit is adapted to cause a particularly sharp increase in optical power. Due to the parasitic effects described above, short light pulses or steep turn-off edges of the LED cannot be realized with this circuit.

The document Wesen, which is incorporated by reference,

[et al.]: "fast way of doing/off-modulation of a LED" ("Fastest method of on/off modulation of LED"), 22 months 6 and 2011, edited in 23 months 6 and 2014, 4. s.url: https: combo/queries/15818/fast-way-of-doing-on-off-modulation-of-a-LED [ search 1/23/2018 ] discloses a control device for an LED with two half-bridges. Other half-bridge control arrangements and half-bridge Drivers not using LEDs are known, for example, from the application guide "TPS 28226 High-Frequency 4-a Sink Synchronous MOSFET Driver" of Texas Instruments (Texas Instruments) and the application guide "2A Synchronous Buck Power MOSFET Driver" for the Microchip product MCP14628 of Microchip (american Microchip) corporation ("2A Synchronous Buck current MOSFET Driver").

EP 2761978B 1 shows an H-bridge for controlling LED light emitting devices of different colors and polarities. But here polarity inversion is used to select different colors. This device is not suitable for emitting short light pulses.

EP 0762651 a2 describes switching on the LED with an initially higher current than the subsequently reduced operating current. This achieves a steep turn-on edge of the light pulse.

DE 102016116718 a1 describes a dimming circuit for LED lamps.

The combination of a light pulse source with a TOF camera (time-of-flight camera) is known, for example, from DE 102014105482 a 1.

JP S587941 also describes a light source for short light pulses with a driver circuit, in which first a positive switch-on pulse is generated and then a negative voltage pulse for switching off the LED is generated.

WO 2016/187566 describes a bipolar control circuit for a laser diode or LED, this control circuit providing two pulses of different polarity and different value and temporally succeeding one another in order to generate ultrashort light pulses in the laser diode or LED with pulse durations in the range of 100 picoseconds to 2 nanoseconds.

US 9,681,514B 1 and US 9,603,210B 1 describe control circuits for switching on LEDs or light emitting diodes, respectively, wherein US 9,681,514B 1 discloses a push-pull control circuit for dimming a light source, wherein the output of this push-pull circuit is operated by means of electrical energy on a positive supply voltage line and a negative supply voltage line.

The publications known in the prior art are mainly concerned with the problem of achieving light pulses with as short rise times as possible. These publications do not address the problem of how to be able to generate an overall very short light pulse in a light emitting diode with a large inherent capacitance and how to deal with the difficulties that arise when lighting fixture LEDs are typically very large in terms of both off-area and capacitance.

There is also a great need in the art for an improved and more reliable measurement system, in particular a LIDAR system. In order to increase the effective range or achieve visibility of dark objects, the sensitivity of the system must be increased. In principle, this can be achieved by photosensitive sensors or by improved emitters (emitting diodes) or by increased emission power. Whereas today's sensors have operated close to physical limits and technical possibilities. In contrast, the transmission power is restricted by law in order to protect people in the vicinity of the system. Therefore, there is a great need for an improved emitting diode for a measurement system, in particular a LIDAR system.

Disclosure of Invention

The solution to this problem is based on the following recognition: the main objective is to optimize the emitting light emitting diodes used as emitting diodes or light sources. In this case, one aspect of the invention relates to the generation of light pulses with as short rise and fall times as steep edges as possible. Another aspect of the invention relates not only to the generation of steep light pulses, but also to particularly short light pulses without slow rise or fall times of the pulse width. In general, in conventional light emitting diodes, parasitic effects of the light emitting diode generally cause longer rise and fall times. This is particularly true for light-emitting diodes used in vehicle technology, in particular if the light-emitting diodes are also used for illumination purposes.

The above-mentioned problem is solved by a light source having the features of claim 1 and by a method having the features of claim 16.

The proposed technical solution considerably shortens the rise time and fall time of the LED light pulse, thus enabling the production of extremely short light pulses with a pulse duration of a few nanoseconds, preferably less than 2 nanoseconds. In particular, the off time of the optical pulse can be significantly shortened. This allows for efficient and high power use of Light Emitting Diodes (LEDs) in applications such as flash LIDAR systems. In many cases, expensive laser diodes can be replaced with LEDs (light emitting diodes).

According to the invention, a light source for generating light pulses with short pulse durations in the nanosecond range comprises a light emitting diode for generating the light pulses and a push-pull circuit for controlling and powering the light emitting diode. The light source may preferably be used in a vehicle, for example to be used as part of a LIDAR system for object recognition and distance measurement.

According to the invention, the light-emitting diode of the light source has a first connection to the output port of the push-pull circuit. The second connection of the light emitting diode is connected to a central potential line, which may preferably be the system ground.

The push-pull circuit has a first input port connected to a first supply voltage line and a potential thereof. The second input of the push-pull circuit is connected to a second supply line and its potential, wherein the second supply line preferably provides a negative potential. The potential of the center potential line (GND) is between the potential of the first power supply line and the potential of the second power supply line.

The push-pull circuit may be switched to a first state in which positive electrical energy of the first supply line is present at the output port. In a second state of the push-pull circuit, a negative electrical energy of the second supply line is present at the output port. The push-pull circuit may be switched back and forth between the first state and the second state.

When the push-pull circuit is switched to the first state and then positive electrical energy is present on the output port, the light emitting diode emits electromagnetic radiation, for example in the form of visible or invisible light or in the infrared region. In this case, there is a positive potential on the first connection of the light-emitting diode which is greater than the potential of the central potential line connected to the second connection of said light-emitting diode.

According to the present invention, the light source is constructed such that a difference between the potential of the central potential line and the potential of the first power supply line is smaller than a difference between the potential of the central potential line and the potential of the second power supply line. That is to say that the absolute value of the positive voltage present at the first connection of a light-emitting diode (LED) in the first state is greater than the absolute value of the negative voltage present at the first connection of this light-emitting diode in the second state.

The LED is switched on in a first state of the push-pull circuit so that charge carriers are accumulated in the light-emitting diode, while in a second state of the push-pull circuit a negative voltage is present across the first connection of the light-emitting diode. By applying a reverse voltage in the blocking direction across the light-emitting diode, the charge stored in the LED need not be eliminated by "radiative recombination" at turn-off, but rather is eliminated primarily by "pumping" by means of an applied reverse field. This removes charge carriers from the space charge region of the LED. The presence of a negative voltage on the first connection of the light-emitting diode causes the light-emitting diode to turn off very quickly. Finally, in the LED, a turn-off pulse with particularly steep edges is thereby generated. In the measuring system, a large turn-off edge of the light pulse of the light-emitting diode leads to a large bandwidth and a correspondingly high resolution. This also enables the overall shortening of the light emission pulse or light pulse of the LED, since the rise time and fall time of the light emission pulse are very short and preferably shorter than 1 ns. The luminaire according to the invention is therefore particularly suitable for use in vehicles.

As described, for example, in EP 0470780 a1, the push-pull circuit according to the invention has no internal current source and therefore no parasitic effects and boundary conditions due to the current source occur either. This circuit is only voltage controlled and not current controlled, thus enabling shorter turn-off times and consequently steeper edges at turn-off.

Contrary to the general technical idea that applying a reverse voltage to a light emitting diode would significantly shorten the lifetime, the present invention just utilizes the application of a reverse voltage. In this case, it has been recognized that the absolute value of the reverse voltage (the potential difference between the second power supply line and the intermediate potential line) may be larger and should be larger than the absolute value of the "forward voltage" (the operating voltage). This is also contrary to the generally accepted expertise.

In the present invention, it has been recognized that the reverse voltage may take a value, for example, equivalent to two or three times the value of the forward voltage of the light emitting diode. Higher blocking voltages, for example values five, ten or twenty times higher than the value of the forward voltage, are preferably also possible. With careful quality management, even a reverse voltage of fifty times the forward voltage can be applied to the light emitting diode without damaging the latter. In the present invention, such reverse voltages or cancellation voltages over the leds have been tested, wherein these cancellation voltages are in the range of 20V to 40V, even up to 60V, whereas for a series circuit with several leds the forward voltage is about 1.2V.

The light source according to the invention is therefore particularly suitable as a light emitter of a LIDAR system. The effect of the fast turn-off and the steep turn-off edges associated therewith establish a particularly large bandwidth of this system. This results in a higher resolution and a larger effective range of the measurement system.

The light source according to the invention and its advantages are particularly embodied in light-emitting diodes for illumination purposes (so-called illumination light-emitting diodes or illumination LEDs). A single-frequency laser diode emits coherent radiation and the charge carrier density in the barrier layer drops rapidly after the highly stimulated emission has been switched off, whereas with illuminated LEDs the barrier layer substantially maintains its state first of all at the switching off, since the stimulated emission is very low. Thus, the illumination LED will continue to emit light for a long time, in any case much longer than the laser diode. Finally, the goal of illuminating leds towards continuing to emit light for long periods of time has been developed in order to achieve a minimum perception of flicker due to pulse width modulation control (PWM). In this regard, the requirements for laser diodes and signaling diodes (signaling light emitting diodes) are in contrast to illumination LEDs. Thus, the illumination LEDs are slower than the faster signal transfer diodes, which have significantly less barrier capacitance.

The barrier capacitance of the laser diode is in the range of about 50 pF. In contrast, the barrier capacitance of a lighting led is about a multiple thereof, typically in the range of a few nanofarads, in particular 10nF to 100 nF.

The illumination LEDs known in the art are typically fluorescent LEDs. Here, the ultraviolet LED irradiates the phosphor layer. But these LEDs cannot be modulated because the phosphor layer continues to emit light. Accordingly, the head lamp generally uses RDG-LEDs in which three-color LEDs, the primary colors of which are self-mixed into white light, are used instead of the white phosphor layer.

Since the illumination LEDs preferably have the advantage of emitting diffuse light, the individual LEDs are preferably controlled and synchronized individually, in particular during the switching-off process, when a negative voltage is present at the first connection of the light-emitting diode.

In a preferred embodiment, the light source comprises three light-emitting diodes, preferably each having a different color, and three driver circuits (push-pull circuits), so that each LED is controlled by the push-pull circuits. The control and synchronization is preferably performed by a control unit which handles the control inputs of the LEDs.

The application of a reverse voltage of greater absolute value compared to the operating voltage leads to a rapid emptying of the space charge region of the light-emitting diode, in particular in illumination LEDs. The barrier capacitance of the diode is rapidly emptied. This effect is particularly pronounced in light emitting diodes with high intrinsic capacitance and inertia. In a preferred embodiment of the invention, the light-emitting diode is used not only as a radiation source or emitter in a measuring system, but at the same time also for illumination purposes, for example as a headlight or vehicle headlight. These leds have a large inertia and intrinsic capacitance, making the circuit according to the invention more efficient. The inertia of the light source is overcome by controlling the light emitting diodes using a push-pull circuit.

In order to simultaneously also be able to use the light-emitting diode as an emitting diode of a measuring system and as a lighting fixture or headlight in a vehicle, the first connection of the light-emitting diode is preferably connected to the third supply voltage by means of a third switch. In this case, the light-emitting diode can be supplied from a third supply line, which also has a positive potential, i.e. a positive voltage is present at the first connection. In this way, the light emitting diode can be used for illumination purposes. The voltage potential of the third power supply line can be selected accordingly. Therefore, the potential of the third power supply line may be independent of the potentials of the other power supply lines, wherein the potential of the first power supply line and the potential of the second power supply line may be different from each other. The push-pull circuit can preferably be switched to a third state in which the output port of this push-pull circuit is separated from the first and second supply lines. Preferably, the above operation is performed when the light source is used for illumination purposes.

It is therefore preferred to switch back and forth between a pulsed mode of operation of the light emitting diodes for the measurement system and a continuous mode of operation with an on-time of at least 1s for illumination purposes. When used in automobiles, the light source is used as a headlamp. During the measurement with the aid of a measuring system (for example a LIDAR system), the headlights which have been switched on are always switched off. The switch-off is usually carried out in a time period of less than or equal to 1ms, preferably in the microsecond range, particularly preferably in the range of less than 1 μ s. And switching the light emitting diode to a pulse working mode within the turn-off time of the third power supply line separated from the light emitting diode, wherein the push-pull circuit does not work in the third state under the pulse working mode. The push-pull circuit is first switched to the first state, thereby turning on the light emitting diode again. The push-pull circuit is then switched to a second state, thereby turning off the light emitting diode. At this time, the blocking capacitance of the light emitting diode is cleared, i.e., charge carriers are discharged out of the space charge region. As mentioned above, a steep turn-off edge will thus be generated to turn off the light emitting diode. The light emitting diodes are then switched to the illumination mode again. The human eye cannot see it because the illumination pattern of the leds is turned off in a time span of less than 1 ms. The user cannot recognize the transition from the illumination mode to the measurement mode. Therefore, there is no limitation in using the light source as a vehicle headlamp.

It has also been recognized in the present invention that it is important to tune the length of time that the reverse voltage or erase voltage is present on the light emitting diode. If the reverse voltage is still present after the space charge region is cleared (barrier capacitance cleared), the light emitting diode can be damaged or destroyed. It has been realized that the length of time the push-pull circuit switches to the second state has to be defined.

In a preferred embodiment of the light source, the light source has a current monitoring circuit, by means of which the discharge current occurring at the light-emitting diode is monitored when the push-pull circuit is switched into the second state. Preferably, the reverse voltage present at the first connection of the light-emitting diode is reduced when the discharge current is below a predetermined current limit value. In this case, the reverse voltage is preferably reduced to a predetermined continuous blocking voltage value. This is a voltage value at which the light emitting diode is not damaged when operating in the blocking mode. It is particularly preferred to reduce the reverse voltage over the light emitting diode below the predetermined continuous blocking voltage value. The continuous blocking voltage value is dependent on the light-emitting diode used and is known or can be determined by simple measurement.

In an equally preferred embodiment, the light source comprises a voltage monitoring unit which monitors the blocking voltage or the reverse voltage present at the light emitting diode when the push-pull circuit is switched into the second state. The discharge of the barrier capacitance is preferably accomplished by means of an elevated voltage across a pre-resistor, which may consist of the internal resistance of the discharge voltage source. The barrier capacitance may short the voltage across the diode if it has not been discharged. As the discharge current decreases, the voltage increases. When the voltage over the light emitting diode exceeds a predetermined voltage limit value, the reverse voltage is reduced, for example to below a predetermined continuous blocking voltage value, preferably to zero. As an alternative, it may also be preferred to separate the second supply voltage of the light source from the output port of the push-pull circuit, so that no voltage in the blocking direction is present anymore at the light emitting diode.

In a further preferred embodiment, the length of time the push-pull circuit switches to the second state is limited. The second state is ended at a predeterminable time point, so that the two states are present only for a predetermined length of time. This point in time can be determined or calculated in case the exact setting of the light source, including all parasitic parameters of all circuit elements, is known in advance. That is, the turn-off time points substantially correspond to the above-mentioned two time points, i.e., when the discharge current is lower than the current limit value or when the erase voltage exceeds the voltage limit value.

The second state of the push-pull circuit is switched off after a predetermined length of time, preferably at most 2 ns. The length of time is particularly preferably at most 1ns, further preferably at most 0.5 ns. For some configurations of the light source, the predetermined point in time is at most 0.2ns, particularly preferably at most 0.1 ns. But the predetermined point in time may also be shorter, for example at most 0.05 ns. In particular in the case of short switching times of the second state, a very short light pulse can be achieved overall in the measuring mode, since the turn-off time is also very short, and therefore the turn-off edge of the light-emitting diode is very steep, which short switching time leads to a very rapid emptying of the barrier capacitance of the light-emitting diode.

In the present invention, it has been recognized that after applying the blocking voltage (reverse voltage) or the cancellation voltage, i.e. after switching the push-pull circuit to the second state, these voltages need to be "normalized" again in order to avoid an avalanche effect in the space charge region of the light emitting diode. The push-pull circuit can therefore preferably be switched to a third state in which the output port is separated from the two supply lines. The third state, in which the output port of the push-pull circuit is separated from the two supply lines, is called the tri-state.

In a preferred embodiment, the light source has a short-circuit line comprising a fourth switch. The short circuit line connects the first terminal of the light emitting diode with the second terminal of the light emitting diode to short-circuit the light emitting diode when the switch is closed. But only when this push-pull circuit has previously switched to its third state will the light emitting diode be short-circuited.

In a further preferred embodiment, the light source comprises a measuring unit or a voltage monitoring unit which measures the open circuit voltage present across the light emitting diode when the push-pull circuit is switched to the third state. The open circuit voltage is preferably measured when the push-pull circuit leaves the second state, i.e. when no negative voltage is present anymore at the first connection of the light emitting diode.

It is particularly preferred to measure the open circuit voltage across the light emitting diode between two control pulses. I.e. when the led is no longer switched to the second state and has not yet been switched to the first state for the next measurement pulse.

In the ideal case, when the push-pull circuit leaves the second state and the first connection of the light-emitting diode is disconnected from the two supply lines, the open-circuit voltage across the light-emitting diode is zero, which corresponds to the third state of the push-pull circuit. The space charge region of the light emitting diode is now completely emptied. If this space charge region still contains charge, the open circuit voltage is not zero. After this, the open circuit voltage will be regulated by adjusting the negative switching pulses at the output port of the push-pull circuit and at the first junction of the light emitting diode.

In a preferred embodiment, the open circuit voltage is adjusted to zero or to a practically negligible value, preferably by fine or fine adjustment of the charging or discharging pulses (positive or negative voltage pulses on the first terminals of the LEDs). This may be achieved, for example, by adjusting the pulse duration and/or the edge steepness of the control pulses or by changing the voltage level of the control pulses (for example by using a charge pump or another, preferably adjustable, voltage boosting unit). This adjustment can be carried out by means of a regulator or a regulating unit.

Alternatively, it is also preferable that the center potential, that is, the potential of the center potential line, may be moved or changed.

In a particularly preferred embodiment, the switching time of the push-pull circuit to the first state is at most 0.5 ns. The switching time is particularly preferably at most 0.2ns, further preferably at most 0.1ns, particularly preferably 0.05 ns. This enables a particularly steep rise of the light pulse emitted by the light-emitting diode. This is also a prerequisite for the emission of as short a light pulse as possible by the light-emitting diode.

In a preferred embodiment of the light source, the light-emitting diode emits short light pulses in the nanosecond range in the electromagnetic radiation. The pulse duration of the generated light pulses is at most 1 ns. The pulse duration of the light pulse is preferably at most 0.7 ns. It is further preferred that the pulse duration of the light pulses emitted by the light emitting diodes is at most 0.5ns, further preferred at most 0.3ns, especially preferred at most 0.1 ns. This may result in a steep and extremely short light pulse, which is sufficient for a LIDAR system. Since this pulse duration is so short, the height of the light pulse can be very high, since only the entire energy content, i.e. the emission power, is limited to a certain limit value. Thus, a LIDAR system with a particularly large effective range can be realized with the light source according to the invention. This effective range is twice the conventional effective range, which is five to ten times the conventional effective range with very short pulse durations. In the case of very narrow pulses, a larger effective range can also be achieved.

In a preferred embodiment, the light source has a charge pump between one of the first or second power supply lines and the output port, thereby increasing the potential of the respective power supply line. This charge pump (charge pump) increases the potential value of the first or second power supply line. Depending on the specific implementation of the charge pump, a voltage doubling or multiple multiplication can be achieved. The polarity of the switching voltage is also conceivable. Of course, other dc voltage converters may be used. This charge pump is preferably arranged between the supply lines and the switching elements in the bundles, so that the capacitance in the charge pump has no or only a negligible effect on the signal waveform for controlling the light-emitting diodes.

When charge pumps are used in the light source, the output terminals of the charge pumps have a potential difference therebetween that is larger than the potential difference between the two supply voltages (the first power supply line and the second power supply line).

The solution of the invention to achieve the above object is also a method for generating light pulses by means of a light-emitting diode, wherein the light-emitting diode can preferably be used in a vehicle. The method comprises providing a light source having a light emitting diode for generating the light pulses, the light emitting diode having a first connection and a second connection, and a push-pull circuit for controlling and powering the light emitting diode. And the first joint of the light emitting diode is connected with the output port of the push-pull circuit. And a second joint of the light emitting diode is connected with the central potential line. According to the invention, the push-pull circuit is switched to a first state, and in the first state, an output port of the push-pull circuit is connected with a first power supply line so as to supply power to the light emitting diode. The potential of the first power supply line is positive and greater than the potential of the central potential line.

According to a further step of the method, the push-pull circuit stays in the first state for a first time period. The first period of time is typically at most 1ns, preferably at most 0.2 ns.

In a further step, the push-pull circuit is switched from a first state to a second state in which an output port of the push-pull circuit is connected to a second supply line. The output port is disconnected from the first power supply line. The potential of the second power supply line is negative and is smaller than the potential of the central potential line. In a further step, the push-pull circuit stays in the second state for a second time period, which is again preferably at most 1ns, preferably at most 0.5 ns. The second time period corresponds to the time until the discharge current does not fall below a predetermined current limit value or the reverse voltage across the light-emitting diode does not exceed a predetermined voltage limit value. The second length of time may also be equal to a predetermined value, which may be determined or calculated knowing all parasitic parameters of the entire configuration.

In this case, the light source is constructed and arranged in such a manner that the difference between the potential of the central potential line and the potential of the first power supply line is smaller than the difference between the potential of the central potential line and the potential of the second power supply line. In other words, the light source is switched in such a way that the reverse voltage or the erase voltage applied to the light emitting diode is larger than the operating voltage of the light emitting diode, preferably by a large multiple.

In a preferred embodiment, the first and second time periods of the method are selected in such a way that the light emitting diode emits light pulses having a pulse duration of at most 1.5ns, preferably at most 1.0 ns. Further preferably, the pulse duration of the light pulses of the light emitting diode is at most 0.7ns, preferably at most 0.5ns, further preferably at most 0.2ns, particularly preferably at most 0.1 ns. The aim is to generate such short light pulses with the light emitting diodes of the light source that the requirements of the measuring system are met.

In a further preferred embodiment of the method according to the invention, the following steps are carried out: and switching the push-pull circuit to a third state in which both power supply lines are separated from the output port. In a further step, the closing of a third switch is completed, which connects the first connection of the light-emitting diode to a third supply line, wherein the potential of the third supply line is positive. The emission of electromagnetic radiation for illumination purposes of the light-emitting diode is thereby accomplished. The light-emitting diode or the light source can therefore be used in particular for illumination purposes, for example as a headlight for a vehicle. The potential of the third power supply line may be different from the potentials of the other potential lines.

In an equally preferred embodiment of the method, the push-pull circuit is switched into its third state in which both supply lines are separated from the output port. In another step, a fourth switch is closed, and the fourth switch closes a short-circuit line between the first terminal of the light-emitting diode and the second terminal of the light-emitting diode, thereby short-circuiting the light-emitting diode.

Of course, it is fully clear to the skilled person that the third switch and the fourth switch must not both be closed at the same time. The control device of the light source according to the invention is constructed accordingly.

The push-pull circuit is preferably switched to the third state by separating the output port from the power supply line. According to the invention, said separation is accomplished by opening the switching elements of the push-pull circuit.

The method preferably has the following steps: monitoring a discharge current present on the light emitting diode when the push-pull circuit is switched to the second state; identifying a current value below a predetermined current limit value; the voltage present at the first connection of the light-emitting diode is reduced, preferably to a predetermined continuous blocking voltage value, particularly preferably to a voltage value below the predetermined continuous blocking voltage value.

The method can also preferably have the following steps: monitoring a voltage present on the light emitting diode when the push-pull circuit is switched to the second state; identifying that a predetermined voltage limit has been exceeded; reducing the voltage present at the first connection of the light-emitting diode, preferably to a predetermined continuous blocking voltage value, particularly preferably to a voltage value below the predetermined continuous blocking voltage value; or to separate the second supply voltage from an output port of the push-pull circuit.

In a preferred embodiment of the method, a measuring device is used to measure the open circuit voltage of the light-emitting diode. In one step, the open circuit voltage over the light emitting diode is measured when the push-pull circuit leaves the second state and has not yet (again) entered the first state. The push-pull circuit is preferably switched to a third state in which the switching element or transistor of the push-pull circuit is blocked and the supply lines are preferably not connected to a light-emitting diode.

The method preferably comprises the further step of: when the push-pull circuit is switched into the first state and/or into the second state, the voltage at the first connection of the light-emitting diode is preferably adjusted by means of a regulator, optionally until the open-circuit voltage at the light-emitting diode is equal to zero. The adjustment is preferably done by changing the voltage on the output port of this push-pull circuit, particularly preferably by using a charge pump.

In a further preferred step, the adjustment of the control pulses is carried out in the second state of the push-pull circuit, preferably by changing the edge steepness or pulse duration of the control pulses applied to the first connection of the light-emitting diode.

For the sake of completeness and clarity, it is noted that a light-emitting diode emits electromagnetic radiation when it is supplied with positive electrical energy. Although theoretically correct, a small amount of electromagnetic radiation is also emitted when the LED is biased in the blocking direction. However, it is not considered that this is only a theoretical point of view, i.e. that the light-emitting diode is considered ideal here, i.e. that it emits light in only one direction when energized, which is true in practice.

Drawings

The invention will be described in detail below with reference to the drawings in connection with selected embodiments. Wherein:

FIG. 1 is a first embodiment of a light source according to the present invention;

FIG. 2 is a second embodiment of a light source according to the present invention;

FIG. 3 is a third embodiment of a light source according to the present invention;

FIG. 4 is a fourth embodiment of a light source with a charge pump according to the present invention;

FIG. 5 is another embodiment of a light source according to the present invention; and

Fig. 6 is a simulation of the current flowing through an LED of a light source according to the invention compared to two LEDs with other interface connections.

Detailed Description

Fig. 1 shows a light source according to the invention with a push-pull circuit 2 and a light-emitting diode 3. The push-pull circuit 2 is used for controlling and powering the light emitting diode 3.

The led has a first terminal 10, which is the anode. The second terminal 12 of the light-emitting diode 3 constitutes the cathode. The first terminal 10 of the light emitting diode 3 is connected to the output port 20 of the push-pull circuit 2. The second terminal 12 is connected to a central potential line 14, also called Ground (GND). The central potential line 14 is preferably the system ground.

The push-pull circuit 2 has a first input port 22 and a second input port 24. The push-pull circuit 2 has two switching elements 26. The switching element 26 located between the first input port 22 and the output port 20 is a first transistor 28. The switching element 26 located between the output port 20 and the second input port 24 is a second transistor 30. The two

transistors

28, 30 are controlled by

control connections

32 and 34, respectively. The control joint is controlled by a control unit 36 for controlling the light source 1. Of course, in contrast to the circuit implemented here by means of the two

transistors

28 and 30, more complex lines of a plurality of electronic components having the same function can also be used.

The first transistor 28 of the push-pull circuit 2 can be switched into the first or second state by means of the first control electrode 38 via the first control connection 32. In a first state of the first transistor 28, the first input port 22 of the push-pull circuit is connected to the output port 20 with a lower resistance than in a second state. This low resistance state in which the first transistor 28 is turned on is referred to as an on state. In this case, the first input port 22 is connected to a first power supply line 42. The potential of the first supply line 42, also referred to as VCC, is positive, so that a positive voltage is present at the anode of the light-emitting diode 3 (first terminal 10) and the light-emitting diode 3 emits electromagnetic radiation in the form of light (visible or invisible) or infrared radiation or ultraviolet radiation.

A second state of the first transistor 28, which is referred to as the off-state, is reached when the first control electrode 38 switches the first transistor 28 high-resistively, i.e. with a resistance which is at least higher than in the first state. The first supply line 42 is then separated from the output port 20 of the push-pull circuit 2, at least in a manner so high-resistively that the light-emitting diode 3 emits no light and emits no or only practically negligible electromagnetic radiation.

The second transistor 30 can also be switched by the control unit 36 via the second control connection 34 and the second control electrode 40 into an on state with low resistance or into an off state with high resistance. In the on-state, the second transistor has a lower resistance than in the off-state, so that the output port 20 is connected to the second power supply line 44 through the second input port 24. The second power supply line 44 is also referred to as (-VCC), and its potential is lower than that of the first power supply line 42. The potential of the second power supply line 44 is preferably negative. The potential of the central potential line 14 is between the potential of the first power supply line 42 and the potential of the second power supply line 44.

In the off state, the second supply line 44 is connected to the output port 20 via the low-resistance switching second transistor 30, so that a negative potential is present at the first connection 10 (anode) of the light-emitting diode 3. Thus, the light emitting diode 3 operates in the blocking direction.

In a first state of the push-pull circuit 2, the first transistor 28 is low-resistive, while the second transistor 30 is switched to high-resistive. This is achieved by a control unit 36, which may be part of the light source 1 or a separate component. In a first state of the push-pull circuit 2, the light-emitting diode 3 emits electromagnetic radiation.

In a second state of the push-pull circuit, the second transistor 30 switches to a low resistance, while the first transistor 28 switches to a high resistance. In this case, a negative potential of the second power supply line 44 exists on the anode of the light emitting diode 3. The light emitting diode 3 is operated in the blocking direction in order to empty the charge in the blocking capacitance of the light emitting diode 3.

In the third state of the push-pull circuit 2, both

transistors

28 and 30 are switched to a high resistance and are thus not connected to either of the two

supply lines

42, 44. In order to solve the problem of the large diode capacitance of the light emitting diode 3, which causes a large inertia of the light emitting pulse of the light emitting diode 3, the present invention proposes that the potential difference between the potential of the first power supply line 42 and the center potential of the center potential line 14 is smaller than the potential difference between the potential of the second power supply line 44 and the center potential of the center potential line 14. This condition is contradictory to the statement to be found in the prior art, i.e. a higher reverse voltage would shorten the service life and should therefore be avoided.

The push-pull circuit 2 can only be switched to the second state for a certain length of time, in which second state the potential of the second supply voltage 44 is present at the first connection 10 of the light-emitting diode 3. As soon as the space charge region or the blocking layer capacitance of the light-emitting diode 3 is emptied, i.e. there are no free charge carriers in the space charge region anymore, the second state of the push-pull circuit 2 has to be ended. For this purpose, for example, the discharge current in the light-emitting diode 3 or the voltage across the light-emitting diode 3 can be measured. If all parameters and parasitic parameters of the wiring of the light source 1 are known, the length of time for operating the push-pull circuit 2 in the second state can be determined and the second state can be ended after a predetermined time.

Fig. 2 shows a preferred embodiment of a light source 1 according to the invention, in which the first connection 10 (anode) of the light-emitting diode 3 is connected to a third supply line 48 by way of a supply line 46. A switch 50, which can also be embodied in the form of a transistor, is arranged in the supply line 46. The closing of the third switch 50 establishes the connection of the anode of the light emitting diode 3 with the third power supply line 48. Preferably, the push-pull circuit 2 switches to the third state when the third switch 50 is closed. In this case, the light emitting diode 3 is supplied with power from the third power supply line 48. This occurs, for example, when the light-emitting diodes 3 are used for illumination purposes in continuous operation, for example as headlights of a vehicle. The potential of the third power supply line 48 is preferably positive.

In a preferred embodiment, the voltage difference between the potential of the third power supply line 48 and the potential of the central potential line 14 is smaller than the voltage difference between the potential of the second power supply line 44 and the potential of the central potential line 14.

Fig. 3 shows an embodiment which is likewise preferred, in which the switching of the short-circuit line 52 by the light-emitting diode 3 is added in comparison with the embodiment shown in fig. 1. The short-circuit line 52 has a fourth switch 54, which is referred to as a short-circuit switch. The led 3 and its space charge region can be standardized by closing the fourth switch 54 in order to prevent an avalanche effect, in particular at the edges of the space charge region. This normalization is done after removing charge carriers from the space charge region or the barrier capacitance. Before the fourth switch 54 can be closed, the push-pull circuit 2 has to be switched to its third state such that its output port 20 is not connected to either of the two

supply lines

42, 44.

Of course, the embodiments shown in fig. 2 and 3 may be combined with each other, so that in case the light emitting diode 3 is further connected with the third power supply line 48, a short-circuit line 52 may also be provided.

Fig. 4 shows a further embodiment of the light source 1, in which a first charge pump 56 is arranged between the first input port 22 of the push-pull circuit 2 and the first supply line 42 in order to raise the potential of the first supply line 42. The charge pump 56 is used to boost the voltage and thereby the potential difference between the first input port 22 of the push-pull circuit and the potential of the central potential line 14.

According to fig. 4, a second charge pump 58 is provided between the second supply line 44 and the second input port 24 of the push-pull circuit in order to increase the absolute value of the potential at the second input port 24. Therefore, when the above-described two charge pumps 56 and 58 are used, the potential difference between the first input port 22 and the second input port 24 is larger than the potential difference between the first power supply line 42 and the second power supply line 44.

Of course, it is also possible to use only one charge pump, for example the first charge pump 56, in the case of light-emitting diodes 3 which are to be switched on as quickly as possible. In the case of leds 3 which are to be switched off particularly rapidly and for which a high reverse voltage in the blocking direction must be present at the led 3, a further option is to use only the second charge pump 58.

Generally, charge pumps generally have only a small charge storage capacity, and therefore, these charge pumps are generally not suitable for long-lasting illumination. Therefore, in case of a hybrid operation for measurement purposes and illumination purposes, the push-pull circuit 2 should be operated in its third state, e.g. by using a multiplexer.

Of course, the use of charge pumps 56 and 58 may be combined with one or both of the embodiments shown in fig. 2 or 3.

Fig. 5 shows a particularly preferred embodiment of the invention. The control unit 36 signals to the regulator 60 via the status and/or synchronization signal sending means 61 which status the device (light source 1) is in. It may be a first state in which the first transistor (T1)28 is turned on and the second transistor (T2)30 is blocked. It may be a second state in which the first transistor 28 is blocked and the second transistor 30 is turned on. It may be a third state in which the first transistor 28 is blocked and the second transistor 30 is blocked. When the LED (light emitting diode 3) is turned on in the first state for a first period of time T₁After switching on, the method enters a second time period T₂Then enters a third state for a third time period T ₃Third form ofState. Preferably, the measuring device or regulator 60 is in the third time period T₃A measuring time point in which the push-pull circuit 2 and thus the light source 1 are in the third state measures the LED residual voltage at the first connection 10 of the light-emitting diode 3 with respect to a reference potential (center potential line 14 or system ground or GND).

If the LED residual voltage is positive, all charge carriers of the space charge region of the light emitting diode 3 are not emptied. In this case, the regulator 60 increases charge extraction in the second state or decreases charge storage in the first state. Improved charge extraction is a preferred option.

The first scheme is that the regulator 60 extends the second period of time T for increased charge extraction₂. To this end, the regulator 60 transmits the extended second time period T to the control unit 36 through the first signal line 62₂Of the signal of (1).

The second solution consists in that the regulator 60 further reduces the negative voltage at the second input port 24 of the push-pull circuit 2 to increase the charge extraction, i.e. to increase the absolute value of this negative voltage. To this end, the regulator 60 delivers the reduced signal, for example via a second signal line 63, to the second charge pump 58 or another voltage regulating device suitable for regulating the potential of the second input port 24.

A less preferred third scheme is that the regulator 60 reduces the positive voltage at the first input port 22 to reduce charge storage. To this end, the regulator 60 delivers the reduced signal, for example, via a third signal line 64 to the first charge pump 56 or another device suitable for regulating the potential of the first input port 22.

If the LED residual voltage is negative, too many charge carriers of the space charge region of the light emitting diode 3 have been removed. In this case, the regulator 60 reduces charge extraction when the push-pull circuit 2 is in the second state or increases charge storage when the push-pull circuit 2 is in the first state. Reducing charge extraction is a preferred option.

Another preferred variant for adjusting the open circuit voltage of the light-emitting diode 3 consists in that the regulator 60 shortens the second time period T₂To reduce charge extraction. To this end, the actuator 60 passes a first signalThe signal line 62 transmits the shortened second period of time T to the control unit 36₂Of the signal of (1).

Another preferred solution is that the regulator 60 further increases the negative voltage at the second input port 24 to reduce charge extraction, i.e. to reduce the absolute value of the negative voltage. To this end, the regulator 60 delivers the increased signal, for example via a second signal line 63, to a second charge pump (58) or another device suitable for regulating the potential of the second input port 24.

A less preferred third scheme is that the regulator 60 steps up the positive voltage at the first input port 22 to increase charge storage. The regulator 60 delivers the increased voltage signal, for example, via a third signal line 64 to the first charge pump 56 or another device suitable for regulating the potential at the first input port 22.

The measuring time point is preferably before the end of the third time period, after the end of the third time period T3 and after the potential at the first connection 10 of the light-emitting diode 3 has stabilized.

The regulator 60 is preferably a PID regulator or a regulator with integrated control features, which regulates the LED residual voltage to zero.

Of course, the adjustment and regulation of the open-circuit voltage of the light-emitting diode 3 and the components necessary for this, which are shown in fig. 5, can be combined with one or more of the embodiments according to fig. 2 to 4. All embodiments shown in fig. 2 to 5 may also be combined.

Fig. 6 shows timing diagrams of simulations of three different drive circuits. The current flowing through the light-emitting diode 3 shown in fig. 1 is recorded over time.

When a current driver with a current intensity of 20mA is used instead of the push-pull circuit, the light emitting diode 3 will generate a current curve c as shown in fig. 5. The use of a voltage driver (3.3V) results in a current curve b. The push-pull circuit 2 according to the invention with a maximum voltage of 40V generates a curve a. It can clearly be seen that the proposed method and the use of the push-pull circuit 2, in which the light emitting diode 3 is switched off by applying a negative voltage of the second supply line 44, enable a significantly shorter pulse of the light emitting diode 3 and a fast switching off.

Claims

1. Light source for generating light pulses with short pulse durations in the nanosecond range, in particular for vehicles, comprising a light emitting diode (3) for generating light pulses and a push-pull circuit (2) for controlling and powering the light emitting diode (3),

wherein

The light-emitting diode (3) has a first connection (10) connected to an output port of the push-pull circuit (2) and a second connection (12) connected to a central potential line (14),

the push-pull circuit (2) has a first input port (22) connected to a first supply line (42) and a second input port (24) connected to a second supply line (44),

the potential of the central potential line (14) is between the potential of the first power supply line (42) and the potential of the second power supply line (44),

the push-pull circuit (2) being switchable to a first state in which positive electrical energy of the first power supply line (42) is present on the output port (20), and to a second state in which negative electrical energy of the second power supply line (44) is present on the output port (20),

the light emitting diode (3) emits electromagnetic radiation when the push-pull circuit (2) is switched to the first state,

The difference between the potential of the central potential line (14) and the potential of the first power supply line (42) is smaller than the difference between the potential of the central potential line (14) and the potential of the second power supply line (44).

2. Light source according to claim 1, characterized in that in the second state of the push-pull circuit (2) the discharge current present at the light emitting diode (3) is monitored and that when the discharge current is below a predetermined current limit value the voltage present at the first connection of the light emitting diode (3) is reduced, preferably to a predetermined continuous blocking voltage value, particularly preferably to a voltage value below the predetermined continuous blocking voltage value.

3. A light source as claimed in claim 1, characterized in that in the second state of the push-pull circuit (2) the voltage present across the light-emitting diode (3) is monitored and a second supply voltage is separated from the output port of the push-pull circuit (2) when the voltage exceeds a predetermined voltage limit value.

4. A light source as claimed in claim 1, characterized in that the switching time for the push-pull circuit (2) to switch into the second state does not exceed a predetermined length of time, which is preferably at most 2ns, further preferably at most 1ns, further preferably at most 0.5ns, further preferably at most 0.2ns, particularly preferably at most 0.1 ns.

5. A light source as claimed in any one of the preceding claims, characterized in that the push-pull circuit (2) comprises two switching elements (26) for interconnecting the output port (20) with the first and second supply lines (42, 44), wherein the switching elements (26) are preferably switches, particularly preferably transistors (28, 30).

6. The luminaire as claimed in the preceding claim, characterized in that the push-pull circuit (2) has two control connections (32, 34), each of which controls one switching element (26).

7. A light source as claimed in any one of the preceding claims, characterized in that the push-pull circuit (2) can be switched into a third state in which the output port (20) is separated from the two supply lines (42, 44).

8. The luminaire as claimed in the preceding claim, characterized in that the first connection (10) of the light-emitting diode (3) is connected to a third supply line (48) via a third switch (50), so that the light-emitting diode (3) can be supplied with power by the third supply line (48) and can be used for lighting purposes.

9. A luminaire as claimed in claim 7, characterized in that a short-circuit line with a fourth switch (54) is provided between the first connection (10) and the second connection (12) of the light-emitting diode (3), which short-circuit line is used to short-circuit the light-emitting diode (3).

10. A light source according to claim 7, characterized in that a measuring device is provided for measuring the open-circuit voltage of the light-emitting diode (3), which measuring device is designed and arranged to measure the open-circuit voltage on the light-emitting diode (3), preferably when the push-pull circuit (2) is switched to the third state.

11. A light source as claimed in any one of the preceding claims, characterized in that the switching time for the push-pull circuit (2) to switch into the first state is at most 1ns, preferably at most 0.5ns, further preferably at most 0.2ns, further preferably at most 0.1ns, especially preferably at most 0.05 ns.

12. A light source as claimed in any one of the preceding claims, characterized in that the light-emitting diode (3) emits light when emitting electromagnetic radiation, and that the pulse duration of the generated light pulses is at most 2ns, preferably at most 1ns, further preferably at most 0.5ns, further preferably at most 0.3ns, particularly preferably at most 0.1 ns.

13. A light source as claimed in any one of the preceding claims, characterized in that the central potential line (14) is a system ground.

14. A power supply according to any one of the preceding claims, characterized in that a charge pump (56, 58) is arranged between one of the supply lines (42, 44) and the output port (20), in order to raise the potential of the respective supply line (42, 44).

15. The light source according to the preceding claim, characterized in that a charge pump (56, 58) is arranged between the supply line (42, 44) and the output port of the push-pull circuit (2), respectively, such that the potential difference between the outputs of the charge pumps (56, 58) is larger than the potential difference between the two supply lines (42, 44).

16. A method for generating short light pulses with a light emitting diode of a light source, in particular for a vehicle, comprising the steps of:

-providing a light source (1) with a light emitting diode (3) for generating said light pulses and a push-pull circuit (2) for controlling and powering said light emitting diode (3), said light emitting diode having a first connection (10) and a second connection (12), wherein said first connection (10) is connected to an output port (20) of said push-pull circuit (2) and said second connection (12) of said light emitting diode (3) is connected to a line of central potential (14),

-switching the push-pull circuit (2) to a first state in which the output port (20) of the push-pull circuit (2) is connected to a first power supply line (42) for supplying power to the light emitting diode (3), wherein the potential of the first power supply line (42) is positive and greater than the potential of the central potential line (14),

-the push-pull circuit (2) stays in the first state for a first time period,

-switching the push-pull circuit (2) to a second state in which the output port (20) of the push-pull circuit (2) is connected with a second power supply line (44), wherein the potential of the second power supply line (44) is negative and smaller than the potential of the central potential line (14),

-the push-pull circuit (2) stays in the second state for a second time period,

-wherein a difference between the potential of the central potential line (14) and the potential of the first power supply line (42) is smaller than a difference between the potential of the central potential line (14) and the potential of the second power supply line (44).

17. Method according to the preceding claim, characterized in that the first time period and the second time period are chosen in such a way that the light emitting diode (3) emits light pulses having a pulse duration of at most 1.5ns, preferably at most 1.0ns, further preferably at most 0.7ns, further preferably at most 0.5ns, further preferably at most 0.2ns, particularly preferably at most 0.1 ns.

18. Method according to any of the preceding claims 16 or 17, characterized in that the duration of the first time period is at most 1ns, preferably at most 0.7ns, further preferably at most 0.5ns, further preferably at most 0.2ns, further preferably at most 0.1ns, particularly preferably at most 0.05ns, and/or the duration of the second time period is at most 1ns, preferably at most 0.7ns, further preferably at most 0.5ns, further preferably at most 0.2ns, further preferably at most 0.1ns, particularly preferably at most 0.05 ns.

19. Method according to any of the preceding claims 16 to 18, characterized by the steps of:

-switching the push-pull circuit (2) to a third state in which both supply lines (42, 44) are separated from the output port (20),

-closing a third switch (50) connecting the first connection (10) of the light emitting diode (3) with a third power supply line (48), wherein the potential of the third power supply line (48) is positive,

-emitting electromagnetic radiation of the light emitting diode (3) for illumination purposes, preferably within a time period of more than one second.

20. Method according to any of the preceding claims 16 to 19, characterized by the steps of:

closing a fourth switch (54) that closes a short circuit line (52) between the first connection (10) of the light emitting diode (3) and the second connection (12) of the light emitting diode (3), thereby short-circuiting the light emitting diode (3).

21. Method according to claim 20 or 22, characterized in that

Switching the push-pull circuit (2) to the third state in such a way that the power supply line (42, 44) is separated from the output port (20) by opening a switching element (26) of the push-pull circuit (2).

22. Method according to any of the preceding claims 17 to 21, characterized in that the steps of:

-monitoring a discharge current present on the light emitting diode (3) when the push-pull circuit (2) is switched to the second state;

-identifying that the discharge current is below a predetermined voltage limit;

-reducing the voltage present on said first connection (10) of said light emitting diode (3), preferably to a predetermined continuous blocking voltage value, particularly preferably to a voltage value lower than said predetermined continuous blocking voltage value.

23. Method according to any of the preceding claims 17 to 24, characterized in that the steps of:

-monitoring the voltage present across the light emitting diode (3) when the push-pull circuit (2) is switched to the second state;

-identifying that the voltage exceeds a predetermined current limit value;

-reducing the voltage present on said first connection (10) of said light emitting diode (3), preferably to a predetermined continuous blocking voltage value, particularly preferably to a voltage value lower than said predetermined continuous blocking voltage value;

or

-separating a second supply voltage (44) from the output port (20) of the push-pull circuit (2).

24. Method according to any of the preceding claims 16 to 23, characterized in that the steps of:

-providing a measuring device for measuring the open circuit voltage of the light emitting diode (3);

-measuring the open circuit voltage over the light emitting diode (3) when the push-pull circuit (2) leaves the second state and is not yet in the first state.

25. Method according to claim 24, characterized in that said further step comprises:

-adjusting the voltage over the first connection (10) of the light emitting diode (3) when the push-pull circuit (2) switches to the first state and/or to the second state, preferably by means of a regulator (60), optionally until the open circuit voltage over the light emitting diode (3) equals zero,

-wherein the adjustment is preferably made by changing the voltage on the output port (20) of the push-pull circuit (2), particularly preferably by using a charge pump (56, 58).

26. The method of claim 24, wherein:

-adjusting the control pulses in the second state of the push-pull circuit (2), preferably by changing the edge steepness or pulse duration of the control pulses present on the first connection (10) of the light emitting diode (3).

27. The method of claim 24, wherein:

-shifting the potential of said central potential line (14), preferably until said open circuit voltage across said light emitting diode (3) equals zero.