CA2875705C - Method and system for pulsing an led light source - Google Patents
Method and system for pulsing an led light source Download PDFInfo
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- CA2875705C CA2875705C CA2875705A CA2875705A CA2875705C CA 2875705 C CA2875705 C CA 2875705C CA 2875705 A CA2875705 A CA 2875705A CA 2875705 A CA2875705 A CA 2875705A CA 2875705 C CA2875705 C CA 2875705C
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- 238000000034 method Methods 0.000 title claims description 32
- 239000003990 capacitor Substances 0.000 claims description 68
- 238000007599 discharging Methods 0.000 claims description 14
- 230000003685 thermal hair damage Effects 0.000 claims description 6
- 230000000737 periodic effect Effects 0.000 claims 2
- 238000010586 diagram Methods 0.000 description 11
- 238000003384 imaging method Methods 0.000 description 8
- 238000005286 illumination Methods 0.000 description 7
- 230000035939 shock Effects 0.000 description 6
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- 230000006378 damage Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 3
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- 238000000917 particle-image velocimetry Methods 0.000 description 2
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Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B39/00—High-speed photography
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/10—Controlling the intensity of the light
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/40—Details of LED load circuits
- H05B45/44—Details of LED load circuits with an active control inside an LED matrix
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- General Physics & Mathematics (AREA)
- Led Devices (AREA)
- Stroboscope Apparatuses (AREA)
- Circuit Arrangement For Electric Light Sources In General (AREA)
Abstract
A circuit is provided including a first light emitting diode having an electrical input port and an electrical output port. The first light emitting diode is for emitting light when electrical current flows between the electrical input port and the electrical output port thereof. The first light emitting diode is coupled to a charge storage component, which is for storing a charge. The circuit further includes a second switch for switchably releasing the stored charge via the first light emitting diode to cause light to be emitted therefrom, as well as a first switch for switching the electrical input port and the electrical output port to a relative potential therebetween. The relative potential is for preventing the first light emitting diode from emitting light therefrom.
Description
Doc. No. 482-03 CA
METHOD AND SYSTEM FOR PULSING AN LED LIGHT SOURCE
FIELD OF THE INVENTION
100011 The invention relates to pulsed light control, and more particularly to a control circuit and method for driving an LED light source for providing pulsed light.
BACKGROUND
100021 High speed photography is widely used in scientific research and in industrial product development. For instance, high speed imaging is a common technique that is used for taking images of the high pressure injection fuel spray in a combustion engine, the development of a shock wave, and combustion flame propagation. To improve image quality and boost the photo capturing speed, high intensity illumination is demanded to enhance the camera exposure.
Typically, a pulsed laser is employed in such imaging systems for generating transient high-speed and high-brightness illumination, providing sufficient exposure in an extremely short exposure duration. Unfortunately, such pulsed lasers are far more costly than a LED system.
[0003] The brightness of an LED is proportional to the current flow. The maximum current is normally limited by the LED thermal damage threshold, since high current produces a large amount of heat that can melt the wire joints and degrade the LED substance.
When an LED is running in pulse mode, the transient current can exceed the continuous wave (CW) current limit, thereby providing brighter lighting than CW mode. The pulsed LED driving method has been well known for increasing the light brightness and extending LED life. Such methods are widely employed in LED flash lighting.
100041 However, currently available LED pulse light source products fail to meet the high intensity illumination requirements of high speed imaging in the previously mentioned application areas, largely due to the challenges of shaping the pulse for ultra-high speed light output. To capture an ultra-high speed motion, the illumination duration is set in the microseconds range. Conventional high speed LED flash lighting systems only produce insufficient light output at such high speed, and thus costly image intensifiers are commonly employed to enhance the image quality.
[0005] It would be advantageous to provide a method and system that overcomes at least some of the disadvantages of the prior art.
SUMMARY OF EMBODIMENTS OF THE INVENTION
[0006] It is an object of at least one embodiment of the present invention to provide a LED
based pulsed light source, being able to generate sub-microsecond high lumens lighting.
[0007] It is an object of at least one embodiment of the present invention to produce high intensity short-pulse illumination suitable for the imaging system without employing an image intensifier.
[0008] According to an aspect of at least one embodiment of the invention, there is provided a method comprising: charging a first capacitor; and providing a first pulse of light, comprising the ordered steps of: switching on a second transistor to discharge the first capacitor via a first light emitting diode having a first electrical input port and a first electrical output port, to cause the first light emitting diode to emit light; switching on a first transistor coupled across the first electrical input port and the first electrical output port, to provide a relative potential between the first electrical input port and the first electrical output port for stopping the first light emitting diode from emitting light; switching off the second transistor to stop the discharge of the first capacitor; and switching off the first transistor to terminate the relative potential between the first electrical input port and the first electrical output port of the first light emitting diode.
[0009] According to an aspect of at least one embodiment of the invention, there is provided a circuit comprising: a first light emitting diode have an electrical input port and an electrical output port, the first light emitting diode for emitting light when electrical current flows between the electrical input port and the electrical output port thereof; a charge storage component for storing charge; a second switch for switchably releasing the charge via the first light emitting diode to cause light to be emitted therefrom; and a first switch for switching the electrical input port and the electrical output port to a relative potential therebetween, the relative potential for preventing the first light emitting diode from emitting light therefrom.
[0010] According to an aspect of at least one embodiment of the invention, there is provided a method comprising: charging a first capacitor; charging a second capacitor; at intervals of one
METHOD AND SYSTEM FOR PULSING AN LED LIGHT SOURCE
FIELD OF THE INVENTION
100011 The invention relates to pulsed light control, and more particularly to a control circuit and method for driving an LED light source for providing pulsed light.
BACKGROUND
100021 High speed photography is widely used in scientific research and in industrial product development. For instance, high speed imaging is a common technique that is used for taking images of the high pressure injection fuel spray in a combustion engine, the development of a shock wave, and combustion flame propagation. To improve image quality and boost the photo capturing speed, high intensity illumination is demanded to enhance the camera exposure.
Typically, a pulsed laser is employed in such imaging systems for generating transient high-speed and high-brightness illumination, providing sufficient exposure in an extremely short exposure duration. Unfortunately, such pulsed lasers are far more costly than a LED system.
[0003] The brightness of an LED is proportional to the current flow. The maximum current is normally limited by the LED thermal damage threshold, since high current produces a large amount of heat that can melt the wire joints and degrade the LED substance.
When an LED is running in pulse mode, the transient current can exceed the continuous wave (CW) current limit, thereby providing brighter lighting than CW mode. The pulsed LED driving method has been well known for increasing the light brightness and extending LED life. Such methods are widely employed in LED flash lighting.
100041 However, currently available LED pulse light source products fail to meet the high intensity illumination requirements of high speed imaging in the previously mentioned application areas, largely due to the challenges of shaping the pulse for ultra-high speed light output. To capture an ultra-high speed motion, the illumination duration is set in the microseconds range. Conventional high speed LED flash lighting systems only produce insufficient light output at such high speed, and thus costly image intensifiers are commonly employed to enhance the image quality.
[0005] It would be advantageous to provide a method and system that overcomes at least some of the disadvantages of the prior art.
SUMMARY OF EMBODIMENTS OF THE INVENTION
[0006] It is an object of at least one embodiment of the present invention to provide a LED
based pulsed light source, being able to generate sub-microsecond high lumens lighting.
[0007] It is an object of at least one embodiment of the present invention to produce high intensity short-pulse illumination suitable for the imaging system without employing an image intensifier.
[0008] According to an aspect of at least one embodiment of the invention, there is provided a method comprising: charging a first capacitor; and providing a first pulse of light, comprising the ordered steps of: switching on a second transistor to discharge the first capacitor via a first light emitting diode having a first electrical input port and a first electrical output port, to cause the first light emitting diode to emit light; switching on a first transistor coupled across the first electrical input port and the first electrical output port, to provide a relative potential between the first electrical input port and the first electrical output port for stopping the first light emitting diode from emitting light; switching off the second transistor to stop the discharge of the first capacitor; and switching off the first transistor to terminate the relative potential between the first electrical input port and the first electrical output port of the first light emitting diode.
[0009] According to an aspect of at least one embodiment of the invention, there is provided a circuit comprising: a first light emitting diode have an electrical input port and an electrical output port, the first light emitting diode for emitting light when electrical current flows between the electrical input port and the electrical output port thereof; a charge storage component for storing charge; a second switch for switchably releasing the charge via the first light emitting diode to cause light to be emitted therefrom; and a first switch for switching the electrical input port and the electrical output port to a relative potential therebetween, the relative potential for preventing the first light emitting diode from emitting light therefrom.
[0010] According to an aspect of at least one embodiment of the invention, there is provided a method comprising: charging a first capacitor; charging a second capacitor; at intervals of one
2 period, discharging the first capacitor via a first light emitting diode having an electrical input port and an electrical output port to cause the first light emitting diode to emit light; and after a known delay substantially less than one period divided by a number of light emission events per period, discharging the second capacitor via a second light emitting diode having an electrical input port and an electrical output port to cause the second light emitting diode to emit light; and Doc. No. 482-03 CA
switching a transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the light emitting diode from emitting light.
[00111 According to an aspect of at least one embodiment of the invention, there is provided a circuit comprising: a first capacitor; a second capacitor; a first light emitting diode having an electrical input port and an electrical output port; a second light emitting diode having an electrical input port and an electrical output port; at least a control circuit for controlling charging of the first capacitor and the second capacitor and for at intervals of one period, discharging the first capacitor via the first light emitting diode to cause the first light emitting diode to emit light for forming a light emission event and after a known delay substantially less than one period divided by a number of light emission events from the circuit per period, discharging the second capacitor via the second light emitting diode to cause the second light emitting diode to emit light to form another light emission event; a first transistor coupled across the electrical input port and the electrical output port of the first light emitting diode to stop the first light emitting diode from emitting light; and a third transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the second light emitting diode from emitting light.
[0012] According to an aspect of at least one embodiment of the invention, there is provided a lighting circuit comprising: a first light emitting device; a charge storage component for storing charge; and a control circuit for sensing a voltage across one of the first light emitting device and the charge storage device to provide sensed voltage and, in dependence upon the first light emitting device, feedback current and sensed voltage, automatically controlling a charge voltage on the charge storage component and a duration of a discharge of the charge storage through the first light emitting device.
BRIEF DESCRIPTION OF THE DRAWINGS
100131 The instant invention will now be described by way of example only, and with reference to the attached drawings, wherein similar reference numerals denote similar elements throughout the several views, and in which:
100141 Figure 1 is a sketch diagram of a light emitting diode driving circuit for driving a light emitting Diode LED.
switching a transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the light emitting diode from emitting light.
[00111 According to an aspect of at least one embodiment of the invention, there is provided a circuit comprising: a first capacitor; a second capacitor; a first light emitting diode having an electrical input port and an electrical output port; a second light emitting diode having an electrical input port and an electrical output port; at least a control circuit for controlling charging of the first capacitor and the second capacitor and for at intervals of one period, discharging the first capacitor via the first light emitting diode to cause the first light emitting diode to emit light for forming a light emission event and after a known delay substantially less than one period divided by a number of light emission events from the circuit per period, discharging the second capacitor via the second light emitting diode to cause the second light emitting diode to emit light to form another light emission event; a first transistor coupled across the electrical input port and the electrical output port of the first light emitting diode to stop the first light emitting diode from emitting light; and a third transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the second light emitting diode from emitting light.
[0012] According to an aspect of at least one embodiment of the invention, there is provided a lighting circuit comprising: a first light emitting device; a charge storage component for storing charge; and a control circuit for sensing a voltage across one of the first light emitting device and the charge storage device to provide sensed voltage and, in dependence upon the first light emitting device, feedback current and sensed voltage, automatically controlling a charge voltage on the charge storage component and a duration of a discharge of the charge storage through the first light emitting device.
BRIEF DESCRIPTION OF THE DRAWINGS
100131 The instant invention will now be described by way of example only, and with reference to the attached drawings, wherein similar reference numerals denote similar elements throughout the several views, and in which:
100141 Figure 1 is a sketch diagram of a light emitting diode driving circuit for driving a light emitting Diode LED.
3 Doc. No. 482-03 CA
[0015] Figure 2 is a simplified timing diagram of a method of switching the MOSFETs Q1 and Q2.
[0016] Figure 3 is a sketch diagram of another light emitting diode driving circuit for driving a light emitting Diode LED.
[0017] Figure 4 shows a control sequence and synchronization of a light source and camera during image recording.
[0018] Figure 5 is a simplified block diagram of a light emitting diode light source.
[0019] Figure 6 shows a layout of the light source comprising multiple LED
drivers.
[0020] Figure 7 illustrates the operation modes of multiple light emitting diodes.
[0021] Figure 8 shows several supported light emitting diode array configurations.
[0022] Figure 9 shows a simplified timing diagram for a double shot implementation.
[0023] Figure 10 is a representation of a photographic image of a shock wave captured using shock wave Schilieren imaging by means of two different camera modes.
DETAILED DESCRIPTION OF EMBODIMENTS
[0024] The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements.
Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
[0025] Referring to Figure 1, shown is a sketch diagram of a light emitting diode driving circuit for driving a light emitting Diode LED. A capacitor in the form of external capacitor CExr is charged by a power supply Vcc via an external resistor RExT. The capacitor and resistor are typically external, but optionally are integrated with the driver circuit. The capacitor CExT is
[0015] Figure 2 is a simplified timing diagram of a method of switching the MOSFETs Q1 and Q2.
[0016] Figure 3 is a sketch diagram of another light emitting diode driving circuit for driving a light emitting Diode LED.
[0017] Figure 4 shows a control sequence and synchronization of a light source and camera during image recording.
[0018] Figure 5 is a simplified block diagram of a light emitting diode light source.
[0019] Figure 6 shows a layout of the light source comprising multiple LED
drivers.
[0020] Figure 7 illustrates the operation modes of multiple light emitting diodes.
[0021] Figure 8 shows several supported light emitting diode array configurations.
[0022] Figure 9 shows a simplified timing diagram for a double shot implementation.
[0023] Figure 10 is a representation of a photographic image of a shock wave captured using shock wave Schilieren imaging by means of two different camera modes.
DETAILED DESCRIPTION OF EMBODIMENTS
[0024] The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements.
Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
[0025] Referring to Figure 1, shown is a sketch diagram of a light emitting diode driving circuit for driving a light emitting Diode LED. A capacitor in the form of external capacitor CExr is charged by a power supply Vcc via an external resistor RExT. The capacitor and resistor are typically external, but optionally are integrated with the driver circuit. The capacitor CExT is
4 Doc. No. 482-03 CA
located close to light emitting diode LED, in order to reduce overall resistance between the capacitor CExT and the light emitting diode LED.
[0026] Two fast switching MOSFETs Q1 and Q2 within the light emitting diode driver circuit support switching so as to pulse energy through the light emitting diode LED.
Low side MOSFET Q2 actuates turning-on of light emitting diode LED, while high side actuates turning-off of light emitting diode LED. As is seen in the figure, when low side MOSFET Q2 is not conducting and high-side MOSFET Q1 is not conducting, energy from Vcc charges capacitor CExT but there is no current flow path through the light emitting diode LED.
When low side MOSFET Q2 is conducting and high-side MOSFET Q1 is not conducting, energy from capacitor CExT flows to ground via light emitting diode LED, low side MOSFET Q2 and resistor RSENS, causing light emitting diode LED to emit light. When low side MOSFET Q2 is conducting and high-side MOSFET Q 1 is conducting, energy from capacitor CExr can still flow to ground, for example via high side MOSFET Q I, low side MOSFET Q2, and resistor RSENS but does not flow through the light emitting diode LED as both poles of the light emitting diode LED
are coupled via high side MOSFET Ql. So long as the voltage drop across MOSFET
Q1 is less than the voltage for switching the light emitting diode LED into a light emitting state, the diode is forced into an off state by turning on high side MOSFET Ql.
[0027] Figure 2 is a simplified timing diagram of a method of switching the MOSFETs Q1 and Q2. Here, a command sequence for the two MOSFETs Q1 and Q2 is shown.
Basically, in this embodiment, Qland Q2 are commanded approximately oppositely with a short phase shift introduced between the opposite signals. Initially, high side MOSFET Q1 is engaged to equalize the potential between the two terminals of the light emitting diode LED, thereby ensuring that light emission does not occur from light emitting diode LED. High side MOSFET
Q1 is then switched OFF, into a non-conducting state, at ti. After a predetermined short delay ¨ the phase shift, low side MOSFET Q2 engages at t2 and causes light emitting diode LED to emit light.
High side MOSFET Q1 engages again at t3 thereby equalizing terminals of the light emitting diode LED and switching the light emitting diode LED into a mode where it does not emit light.
The light emitting diode LED light output duration is thus determined by t3-t2. Low side MOSFET Q2 is then switched off starting at either t3 or t4. Such a process provides excellent control of light pulse timing both for switching the light on and for switching the light off ¨
Doc. NO. 482-03 CA
controlling the pulse duration. The process is repeatable, and for pulsed light the process is repeated at a known frequency.
[0028] Advantageously, a dual MOSFET driving methodology and circuit as presented allows for shaping of emitted light pulses. The light emitting diode is driven in overcurrent - up to 300A
in transient - to generate high lumen output light. Handling switching of high current relies upon high performance MOSFETs and optimized circuit board design. With current state-of-art MOSFETs and matched gate drivers, switching rise time is fast enough to support a sharp rise of intensity for output light. Unfortunately, cutting off high current may generate undesired oscillation affecting switching from emitting light to a mode where light is not emitted. The function of Q1 offers fast turn-off of light emitted from light emitting diode light and eliminates uncertainties during transition; the transition from light emitting mode to a mode where light is other than emitted relies on equalization of potential across the light emitting diode - two poles of the light emitting diode are at a same or similar potential, thereby forcedly cutting off current across the light emitting diode. This provides improved timing control and is useful for capturing of some images.
[0029] Referring to Figure 3, shown is a sketch diagram of another light emitting diode driving circuit for driving a light emitting Diode LED. Two external capacitors are series connected to provide a voltage reference; typically half of the power supply voltage when two identical capacitors are employed. One of the LED poles is connected to the voltage reference between the two capacitors, and the other pole is connected between the two MOSFETs. The driving scheme is similar to the figure 2. At ti, when the MOSFET Q 1 is conducting and Q2 is not conducting, the LED is at reverse state (the negative pole of the LED has higher potential than the positive pole), and thus there is no current flow. At t2, the MOSFET Q1 is not conducting and the Q2 is conducting, the energy in the two external capacitors discharge through the LED and the LED
emits light. At t3, the MOSFET Q1 turns on and raises the potential at the LED
negative pole, when the potential at the LED negative pole becomes higher than the potential at the positive pole, the LED stops emitting light. The LED light emitting duration is determined by t2 and t3.
At t4, the MOSFET Q2 turns off and there is no current flow through either LED
or MOSFET.
The LED can be configured at a different polarization; correspondingly, the two MOSFETs should be driven in the opposite sequence to that shown in figure 2. In this diving scheme, Doc. No. 482-03 CA
instead of equalizing the potential between the LED to turn off the light emitting, the LED on/off is controlled by electrically pulling up/down one pole of the LED. A fast recovery diode is connected to the negative pole of the LED for over voltage protection.
[0030] Figure 3 shows a control sequence and synchronization of the light source and a camera during image capture. The camera operates in high-speed mode, with an exposure period covering the light emitting diode's light emitting time. Each image frame records a phenomenon at a time illuminated by a light emission within a strobed light emission.
Thus, very sharp images, even of fast moving items, can be captured. In another camera mode, a longer exposure time covering multiple light emitting diode light emitting events is used allowing for superposition within a single frame of several "snapshots" in time.
Progression of a physics phenomenon is recoded in successive frames in the first mode and in one image frame in the second mode. This, for instance, allows measurement of flame propagation, shock wave fronts, spray development processes, and many other transient processes for visualization. Sharp shaping of light pulse with a fast rise time and a fast fall time across the light emitting diode, and high speed of a light pulse both for accuracy of timing and for pulse duration, is sometimes critical for visual descriptions of these crucial developments and formations.
[0031] Referring to Figure 4, shown is a simplified block diagram of a light emitting diode light source. The block diagram is for a programmable light source and includes programmable control IC. The programmable IC generates control signals for switching the low side MOSFET
Q2 and the high side MOSFET Q1 within the LED Driver block. The LED driver block includes light emitting diode(s), charge storage in the form of capacitors, a power source and Q1 and Q2.
Alternatively, the LED driver includes a power port for receiving external power therefrom. As shown, the LED driver includes a feedback path to provide the programmable control IC with information about charge on the charge storage. The intelligent control unit includes a communication interface for communicating with the programmable control IC as well as other circuitry such as a trigger circuit, a timer circuit, a conditioning circuit for signal conditioning and an optional display. The trigger circuit and the timer circuit act to determine pulse spacing and width to provide both frequency and duty cycle control. Alternatively, the trigger circuit and the timer circuit act to determine pulse spacing and width and interleaving to provide frequency, Doc. No. 482-03 CA
duty cycle, and in period on-off characteristic control. Of course, the same circuitry also supports single pulses, for example for flash photography.
[0032] Control signals for triggering - for driving - the MOSFETs optionally are provided from a same pulse width modulation (PWM) module. As shown in Figure 1, when a pulse such as that shown in Figure 2 is used, the signal is provided from the PWM and the second signal Q2 is inverted and delayed. Alternatively, the signal provided is delayed to form the signal for Q2 and inverted to form the signal for Q 1 . Alternatively, each signal for driving Q1 and Q2 are generated separately. Further alternatively, the signal for Q1 triggers the signal for Q2. Because the delay ¨ the phase shift ¨ is circuit dependent, it has a range of values supported but does not need to be adjusted for a given frequency. Thus, once the delay is determined for a circuit, the same delay is applicable at all frequencies of operation for that circuit given that the delay does not render the circuit non-functional.
[0033] In an embodiment, voltage and current sensing signals are connected to a pulse width adjustment module. Pulse width is then adjusted based on predetermined thermal damage thresholds, thereby protecting the light emitting diode LED. Of course, when the predetermined thermal damage thresholds are unchanging, the pulse width is optionally designed into the circuit in a fixed fashion. When the predetermined thermal damage thresholds vary over time, providing a pulse width adjustment module allows for pulse width changes in response to changing thresholds. In some embodiments, a fast recovery diode (shown in Figure 1 in shadow) is reversely paralleled to the light emitting diode LED to cancel the reverse high voltage during the action of MOSFETs, protecting the light emitting diode LED from the high voltage damage.
[0034] An embodiment of the light source comprises several functions for intelligent control and supporting a user-friendly interface. This is discussed with reference to Figure 4. A variable voltage module is employed to regulate flexibly a capacitor charging voltage in order to support different light emitting diodes and in order to meet requirements of varied current levels at various pulse widths. When pulse duration is shortened to enhance imaging speed, more light lumens is often demanded and achievable through augmenting current. The shorter the pulse duration, the higher the current that can be applied across the light emitting diode without likely damaging the light emitting diode. Transient current is determined based on voltage applied Doc. No. 482-03 CA
across the light emitting diode, since resistance along a current path is often fixed with the circuit layout. Thus voltage is set for a given pulse width to provide optimal output light according to imaging or other needs. The module also includes a circuit for draining the charge storage device in the form of the capacitor to reduce capacitor voltage if and when a lower voltage is needed.
Alternatively, increased lumens are provided by increasing a number of light emitting diodes that are driven simultaneously.
[0035] The programmable control IC is adapted for intelligent control of voltage and PWM. In an embodiment, a voltage to pulse width relation is pre-set in the control IC
to automatically adjust the voltage according to the pulse width setting. Alternatively, both the pulse width and voltage are programmable. For the purpose of optical alignment, the voltage can be set at a low voltage which allows continuously low intensity light emitting without overheating the LED.
The voltage and current are sensed and fed back to the control IC for further refinement. There is also a current to pulse width relation defining a maximum current threshold.
In the presented embodiment, whenever an undesired high current spike occurs and exceeds a predetermined duration, MOSFET Q1 engages to protect LED.
[0036] The light emitting diode is a single high lumens light emitting diode.
Alternatively, an array of light emitting diodes having a total lumen output brightness to meet specified requirements is provided. In the diagram of Figure 4, the light source has a communication interface in the form of a universal serial bus interface (USB) for connecting to a personal computer (PC) or other terminal for programming and setting the controller.
[0037] A timer circuit is embedded in the intelligent control unit, serving as the internal clock for pulse width modulation generation and signal synchronization. An input trigger signal for the circuit has two triggers - one is from an external user-defined TTL pulse and another is generated by a push button. The input trigger signal is then processed by a signal-conditioning unit for eliminating signal errors. For example, the signal is subject to debounce filtering to prevent one button press from registering as multiple button presses in rapid succession.
Based on the internal timer clock, the control unit refines the signal so that the light source is more accommodating to differing input signal quality. In addition to pre-set or controllable parameters through PC software, an onboard input port and display unit is employed to receive and display Doc. No. 482-03 CA
settings of the parameters as they currently stand. Alternatively, the circuit communicates with another computer for providing an indication of the parameters and an opportunity to modify said parameters.
[0038] The light source is also configurable to operate multiple light emitting diodes. By positioning light emitting diodes in predetermined patterns or, alternatively, close together, a plurality of light emitting diodes is switched to emit light simultaneously, thereby increasing output light without increasing current flowing through a single light emitting diode. Figure 5 shows a layout of a light source comprising multiple light emitting diode drivers ¨ each light emitting diode is shown with its own driver. Alternatively, a single driver drives more than one light emitting diode. In the configuration of Figure 5, a control unit receives a start-up trigger signal and in response thereto distributes control signals to multiple light emitting diode drivers for driving each light emitting diode separately but with related timing This configuration supports simultaneous light emission or closely strobed light emission, wherein some driver circuits switch a light emitting diode shortly after others.
[0039] Figure 6 illustrates the operation modes of multiple light emitting diodes. In light emitting diode mode A, the multiple light emitting diodes are operated with a synchronized schedule such that all light emitting diodes emit light simultaneously; the overall light intensity of each individual flash event is thus multiplied. In light emitting diode mode B, one light emitting diode (or a group of synchronized light emitting diodes) emits light during the dwell of another light emitting diode (or a group of synchronized light emitting diodes). The overall illumination frequency is doubled or a pattern of illumination is thereby created but the emitted light intensity is only that of the light emitting diodes that emit light simultaneously.
Alternatively, three or more groups of light emitting diodes are used. More groups of light emitting diodes allows for increased frequency without increased current to each light emitting diode or for more complex patterns of light emission.
[0040] For high lumens light emitting diodes that operate in overcurrent pulse mode, there are two common causes of damage. A first one is fusing of bond wires due to the current overflow;
this occurs when current exceeds a certain threshold. A second one is non-reversible degradation due to high repetitive frequency that sometimes happens even while maintaining a current lower Doc. No. 482-03 CA
than the threshold current. Configuring the lighting circuit with multiple light emitting diodes is beneficial for preventing or reducing a likelihood of each of these sources of light emitting diode damage. That said, multiple light emitting diodes increases an area on a semiconductor that is used and, as such, a cost benefit trade-off exists.
[0041] Another method for use of the above noted control circuitry supports different operating modes of the light emitting diode. Figure 7 shows several supported light emitting diode array layouts. In a single driver configuration, the light emitting diodes are either series or parallel connected, shown in Figure 7 (a) and (b), respectively. For these layouts, the light emitting diodes are operated simultaneously, in Mode A of Figure 6. That said, each configuration has advantages and disadvantages relative to the control circuit as will be understood by those of skill in the art. In a separated layout shown in Figure 7 part (c), the light emitting diodes are mounted closely but isolated one from another and each light emitting diode is driven and controlled separately. Of course, the term closely depends on the application within this layout.
For example, the light emitting diodes are operated in either synchronization Mode A or B of Figure 6. Since the size of a high lumens light emitting diode is only several square millimeters, the layout of a few light emitting diodes is still relatively small and compact. Thus the light emitting diode array is positioned to share a same optical lens for converging or collimating light emitted therefrom. Alternatively, the light emitting diodes are positioned in a configuration dictated by design or other requirements. For example, they are disposed in a ring for disposal about a camera lens.
[0042] The circuit described supports external control thereof. For example, pulse width is adjustable as is pulse period. When multiple light emitting diodes are used on a single circuit, each fired by separate control circuitry, the control circuitry can be synchronized to support faster strobing through cycling through different light emitting diodes for each pulse ¨ for example doubling the frequency has half the diodes light up and then the other half for providing strobe lighting with same period between light emission. Alternatively, the period between light emitting events of different groups of light emitting diodes is also controllable. In this fashion, the light source can be operated as a single-shot ¨ only one group of light emitting diodes lighting each period or two groups of light emitting diodes lighting at once, as a double-shot -with two groups of light emitting diodes lighting one immediately after another to provide two Doc. No. 482-03 CA
strobes closely offset, and a repetitive-pulse mode ¨ where groups of light emitting diodes alternate with a consistent period between lighting emissions. Timing for a double shot implementation is shown in Figure 8. Relying on double shots with the control circuitry synchronized one to another, an imaging technique where two strobed lighting events are superimposed within a single camera frame is achievable. As the double shot is optionally repeated at a known frequency, double shot strobe lighting is supported allowing for multiple sequential double-shots within each sequential camera frame period. This is useable for high speed Particle image velocimetry (PIV) measurement and other velocity related measurement.
[0043] Figure 9 is an image captured using a multiple shot strobe lighting source according to at least an embodiment described above. As noted, multiple shock wave fronts ¨
the shock wave front at multiple locations are captured within a single image in mode B.
[0044] Numerous other embodiments may be envisaged without departing from the scope of the invention.
located close to light emitting diode LED, in order to reduce overall resistance between the capacitor CExT and the light emitting diode LED.
[0026] Two fast switching MOSFETs Q1 and Q2 within the light emitting diode driver circuit support switching so as to pulse energy through the light emitting diode LED.
Low side MOSFET Q2 actuates turning-on of light emitting diode LED, while high side actuates turning-off of light emitting diode LED. As is seen in the figure, when low side MOSFET Q2 is not conducting and high-side MOSFET Q1 is not conducting, energy from Vcc charges capacitor CExT but there is no current flow path through the light emitting diode LED.
When low side MOSFET Q2 is conducting and high-side MOSFET Q1 is not conducting, energy from capacitor CExT flows to ground via light emitting diode LED, low side MOSFET Q2 and resistor RSENS, causing light emitting diode LED to emit light. When low side MOSFET Q2 is conducting and high-side MOSFET Q 1 is conducting, energy from capacitor CExr can still flow to ground, for example via high side MOSFET Q I, low side MOSFET Q2, and resistor RSENS but does not flow through the light emitting diode LED as both poles of the light emitting diode LED
are coupled via high side MOSFET Ql. So long as the voltage drop across MOSFET
Q1 is less than the voltage for switching the light emitting diode LED into a light emitting state, the diode is forced into an off state by turning on high side MOSFET Ql.
[0027] Figure 2 is a simplified timing diagram of a method of switching the MOSFETs Q1 and Q2. Here, a command sequence for the two MOSFETs Q1 and Q2 is shown.
Basically, in this embodiment, Qland Q2 are commanded approximately oppositely with a short phase shift introduced between the opposite signals. Initially, high side MOSFET Q1 is engaged to equalize the potential between the two terminals of the light emitting diode LED, thereby ensuring that light emission does not occur from light emitting diode LED. High side MOSFET
Q1 is then switched OFF, into a non-conducting state, at ti. After a predetermined short delay ¨ the phase shift, low side MOSFET Q2 engages at t2 and causes light emitting diode LED to emit light.
High side MOSFET Q1 engages again at t3 thereby equalizing terminals of the light emitting diode LED and switching the light emitting diode LED into a mode where it does not emit light.
The light emitting diode LED light output duration is thus determined by t3-t2. Low side MOSFET Q2 is then switched off starting at either t3 or t4. Such a process provides excellent control of light pulse timing both for switching the light on and for switching the light off ¨
Doc. NO. 482-03 CA
controlling the pulse duration. The process is repeatable, and for pulsed light the process is repeated at a known frequency.
[0028] Advantageously, a dual MOSFET driving methodology and circuit as presented allows for shaping of emitted light pulses. The light emitting diode is driven in overcurrent - up to 300A
in transient - to generate high lumen output light. Handling switching of high current relies upon high performance MOSFETs and optimized circuit board design. With current state-of-art MOSFETs and matched gate drivers, switching rise time is fast enough to support a sharp rise of intensity for output light. Unfortunately, cutting off high current may generate undesired oscillation affecting switching from emitting light to a mode where light is not emitted. The function of Q1 offers fast turn-off of light emitted from light emitting diode light and eliminates uncertainties during transition; the transition from light emitting mode to a mode where light is other than emitted relies on equalization of potential across the light emitting diode - two poles of the light emitting diode are at a same or similar potential, thereby forcedly cutting off current across the light emitting diode. This provides improved timing control and is useful for capturing of some images.
[0029] Referring to Figure 3, shown is a sketch diagram of another light emitting diode driving circuit for driving a light emitting Diode LED. Two external capacitors are series connected to provide a voltage reference; typically half of the power supply voltage when two identical capacitors are employed. One of the LED poles is connected to the voltage reference between the two capacitors, and the other pole is connected between the two MOSFETs. The driving scheme is similar to the figure 2. At ti, when the MOSFET Q 1 is conducting and Q2 is not conducting, the LED is at reverse state (the negative pole of the LED has higher potential than the positive pole), and thus there is no current flow. At t2, the MOSFET Q1 is not conducting and the Q2 is conducting, the energy in the two external capacitors discharge through the LED and the LED
emits light. At t3, the MOSFET Q1 turns on and raises the potential at the LED
negative pole, when the potential at the LED negative pole becomes higher than the potential at the positive pole, the LED stops emitting light. The LED light emitting duration is determined by t2 and t3.
At t4, the MOSFET Q2 turns off and there is no current flow through either LED
or MOSFET.
The LED can be configured at a different polarization; correspondingly, the two MOSFETs should be driven in the opposite sequence to that shown in figure 2. In this diving scheme, Doc. No. 482-03 CA
instead of equalizing the potential between the LED to turn off the light emitting, the LED on/off is controlled by electrically pulling up/down one pole of the LED. A fast recovery diode is connected to the negative pole of the LED for over voltage protection.
[0030] Figure 3 shows a control sequence and synchronization of the light source and a camera during image capture. The camera operates in high-speed mode, with an exposure period covering the light emitting diode's light emitting time. Each image frame records a phenomenon at a time illuminated by a light emission within a strobed light emission.
Thus, very sharp images, even of fast moving items, can be captured. In another camera mode, a longer exposure time covering multiple light emitting diode light emitting events is used allowing for superposition within a single frame of several "snapshots" in time.
Progression of a physics phenomenon is recoded in successive frames in the first mode and in one image frame in the second mode. This, for instance, allows measurement of flame propagation, shock wave fronts, spray development processes, and many other transient processes for visualization. Sharp shaping of light pulse with a fast rise time and a fast fall time across the light emitting diode, and high speed of a light pulse both for accuracy of timing and for pulse duration, is sometimes critical for visual descriptions of these crucial developments and formations.
[0031] Referring to Figure 4, shown is a simplified block diagram of a light emitting diode light source. The block diagram is for a programmable light source and includes programmable control IC. The programmable IC generates control signals for switching the low side MOSFET
Q2 and the high side MOSFET Q1 within the LED Driver block. The LED driver block includes light emitting diode(s), charge storage in the form of capacitors, a power source and Q1 and Q2.
Alternatively, the LED driver includes a power port for receiving external power therefrom. As shown, the LED driver includes a feedback path to provide the programmable control IC with information about charge on the charge storage. The intelligent control unit includes a communication interface for communicating with the programmable control IC as well as other circuitry such as a trigger circuit, a timer circuit, a conditioning circuit for signal conditioning and an optional display. The trigger circuit and the timer circuit act to determine pulse spacing and width to provide both frequency and duty cycle control. Alternatively, the trigger circuit and the timer circuit act to determine pulse spacing and width and interleaving to provide frequency, Doc. No. 482-03 CA
duty cycle, and in period on-off characteristic control. Of course, the same circuitry also supports single pulses, for example for flash photography.
[0032] Control signals for triggering - for driving - the MOSFETs optionally are provided from a same pulse width modulation (PWM) module. As shown in Figure 1, when a pulse such as that shown in Figure 2 is used, the signal is provided from the PWM and the second signal Q2 is inverted and delayed. Alternatively, the signal provided is delayed to form the signal for Q2 and inverted to form the signal for Q 1 . Alternatively, each signal for driving Q1 and Q2 are generated separately. Further alternatively, the signal for Q1 triggers the signal for Q2. Because the delay ¨ the phase shift ¨ is circuit dependent, it has a range of values supported but does not need to be adjusted for a given frequency. Thus, once the delay is determined for a circuit, the same delay is applicable at all frequencies of operation for that circuit given that the delay does not render the circuit non-functional.
[0033] In an embodiment, voltage and current sensing signals are connected to a pulse width adjustment module. Pulse width is then adjusted based on predetermined thermal damage thresholds, thereby protecting the light emitting diode LED. Of course, when the predetermined thermal damage thresholds are unchanging, the pulse width is optionally designed into the circuit in a fixed fashion. When the predetermined thermal damage thresholds vary over time, providing a pulse width adjustment module allows for pulse width changes in response to changing thresholds. In some embodiments, a fast recovery diode (shown in Figure 1 in shadow) is reversely paralleled to the light emitting diode LED to cancel the reverse high voltage during the action of MOSFETs, protecting the light emitting diode LED from the high voltage damage.
[0034] An embodiment of the light source comprises several functions for intelligent control and supporting a user-friendly interface. This is discussed with reference to Figure 4. A variable voltage module is employed to regulate flexibly a capacitor charging voltage in order to support different light emitting diodes and in order to meet requirements of varied current levels at various pulse widths. When pulse duration is shortened to enhance imaging speed, more light lumens is often demanded and achievable through augmenting current. The shorter the pulse duration, the higher the current that can be applied across the light emitting diode without likely damaging the light emitting diode. Transient current is determined based on voltage applied Doc. No. 482-03 CA
across the light emitting diode, since resistance along a current path is often fixed with the circuit layout. Thus voltage is set for a given pulse width to provide optimal output light according to imaging or other needs. The module also includes a circuit for draining the charge storage device in the form of the capacitor to reduce capacitor voltage if and when a lower voltage is needed.
Alternatively, increased lumens are provided by increasing a number of light emitting diodes that are driven simultaneously.
[0035] The programmable control IC is adapted for intelligent control of voltage and PWM. In an embodiment, a voltage to pulse width relation is pre-set in the control IC
to automatically adjust the voltage according to the pulse width setting. Alternatively, both the pulse width and voltage are programmable. For the purpose of optical alignment, the voltage can be set at a low voltage which allows continuously low intensity light emitting without overheating the LED.
The voltage and current are sensed and fed back to the control IC for further refinement. There is also a current to pulse width relation defining a maximum current threshold.
In the presented embodiment, whenever an undesired high current spike occurs and exceeds a predetermined duration, MOSFET Q1 engages to protect LED.
[0036] The light emitting diode is a single high lumens light emitting diode.
Alternatively, an array of light emitting diodes having a total lumen output brightness to meet specified requirements is provided. In the diagram of Figure 4, the light source has a communication interface in the form of a universal serial bus interface (USB) for connecting to a personal computer (PC) or other terminal for programming and setting the controller.
[0037] A timer circuit is embedded in the intelligent control unit, serving as the internal clock for pulse width modulation generation and signal synchronization. An input trigger signal for the circuit has two triggers - one is from an external user-defined TTL pulse and another is generated by a push button. The input trigger signal is then processed by a signal-conditioning unit for eliminating signal errors. For example, the signal is subject to debounce filtering to prevent one button press from registering as multiple button presses in rapid succession.
Based on the internal timer clock, the control unit refines the signal so that the light source is more accommodating to differing input signal quality. In addition to pre-set or controllable parameters through PC software, an onboard input port and display unit is employed to receive and display Doc. No. 482-03 CA
settings of the parameters as they currently stand. Alternatively, the circuit communicates with another computer for providing an indication of the parameters and an opportunity to modify said parameters.
[0038] The light source is also configurable to operate multiple light emitting diodes. By positioning light emitting diodes in predetermined patterns or, alternatively, close together, a plurality of light emitting diodes is switched to emit light simultaneously, thereby increasing output light without increasing current flowing through a single light emitting diode. Figure 5 shows a layout of a light source comprising multiple light emitting diode drivers ¨ each light emitting diode is shown with its own driver. Alternatively, a single driver drives more than one light emitting diode. In the configuration of Figure 5, a control unit receives a start-up trigger signal and in response thereto distributes control signals to multiple light emitting diode drivers for driving each light emitting diode separately but with related timing This configuration supports simultaneous light emission or closely strobed light emission, wherein some driver circuits switch a light emitting diode shortly after others.
[0039] Figure 6 illustrates the operation modes of multiple light emitting diodes. In light emitting diode mode A, the multiple light emitting diodes are operated with a synchronized schedule such that all light emitting diodes emit light simultaneously; the overall light intensity of each individual flash event is thus multiplied. In light emitting diode mode B, one light emitting diode (or a group of synchronized light emitting diodes) emits light during the dwell of another light emitting diode (or a group of synchronized light emitting diodes). The overall illumination frequency is doubled or a pattern of illumination is thereby created but the emitted light intensity is only that of the light emitting diodes that emit light simultaneously.
Alternatively, three or more groups of light emitting diodes are used. More groups of light emitting diodes allows for increased frequency without increased current to each light emitting diode or for more complex patterns of light emission.
[0040] For high lumens light emitting diodes that operate in overcurrent pulse mode, there are two common causes of damage. A first one is fusing of bond wires due to the current overflow;
this occurs when current exceeds a certain threshold. A second one is non-reversible degradation due to high repetitive frequency that sometimes happens even while maintaining a current lower Doc. No. 482-03 CA
than the threshold current. Configuring the lighting circuit with multiple light emitting diodes is beneficial for preventing or reducing a likelihood of each of these sources of light emitting diode damage. That said, multiple light emitting diodes increases an area on a semiconductor that is used and, as such, a cost benefit trade-off exists.
[0041] Another method for use of the above noted control circuitry supports different operating modes of the light emitting diode. Figure 7 shows several supported light emitting diode array layouts. In a single driver configuration, the light emitting diodes are either series or parallel connected, shown in Figure 7 (a) and (b), respectively. For these layouts, the light emitting diodes are operated simultaneously, in Mode A of Figure 6. That said, each configuration has advantages and disadvantages relative to the control circuit as will be understood by those of skill in the art. In a separated layout shown in Figure 7 part (c), the light emitting diodes are mounted closely but isolated one from another and each light emitting diode is driven and controlled separately. Of course, the term closely depends on the application within this layout.
For example, the light emitting diodes are operated in either synchronization Mode A or B of Figure 6. Since the size of a high lumens light emitting diode is only several square millimeters, the layout of a few light emitting diodes is still relatively small and compact. Thus the light emitting diode array is positioned to share a same optical lens for converging or collimating light emitted therefrom. Alternatively, the light emitting diodes are positioned in a configuration dictated by design or other requirements. For example, they are disposed in a ring for disposal about a camera lens.
[0042] The circuit described supports external control thereof. For example, pulse width is adjustable as is pulse period. When multiple light emitting diodes are used on a single circuit, each fired by separate control circuitry, the control circuitry can be synchronized to support faster strobing through cycling through different light emitting diodes for each pulse ¨ for example doubling the frequency has half the diodes light up and then the other half for providing strobe lighting with same period between light emission. Alternatively, the period between light emitting events of different groups of light emitting diodes is also controllable. In this fashion, the light source can be operated as a single-shot ¨ only one group of light emitting diodes lighting each period or two groups of light emitting diodes lighting at once, as a double-shot -with two groups of light emitting diodes lighting one immediately after another to provide two Doc. No. 482-03 CA
strobes closely offset, and a repetitive-pulse mode ¨ where groups of light emitting diodes alternate with a consistent period between lighting emissions. Timing for a double shot implementation is shown in Figure 8. Relying on double shots with the control circuitry synchronized one to another, an imaging technique where two strobed lighting events are superimposed within a single camera frame is achievable. As the double shot is optionally repeated at a known frequency, double shot strobe lighting is supported allowing for multiple sequential double-shots within each sequential camera frame period. This is useable for high speed Particle image velocimetry (PIV) measurement and other velocity related measurement.
[0043] Figure 9 is an image captured using a multiple shot strobe lighting source according to at least an embodiment described above. As noted, multiple shock wave fronts ¨
the shock wave front at multiple locations are captured within a single image in mode B.
[0044] Numerous other embodiments may be envisaged without departing from the scope of the invention.
Claims (29)
1. A method comprising:
charging a first capacitor; and providing a first pulse of light, comprising the ordered steps of:
switching on a second transistor to discharge the first capacitor via a first light emitting diode having a first electrical input port and a first electrical output port, to cause the first light emitting diode to emit light;
switching on a first transistor coupled across the first electrical input port and the first electrical output port, to provide a relative potential between the first electrical input port and the first electrical output port for stopping the first light emitting diode from emitting light;
switching off the second transistor to stop the discharge of the first capacitor; and switching off the first transistor to terminate the relative potential between the first electrical input port and the first electrical output port of the first light emitting diode.
charging a first capacitor; and providing a first pulse of light, comprising the ordered steps of:
switching on a second transistor to discharge the first capacitor via a first light emitting diode having a first electrical input port and a first electrical output port, to cause the first light emitting diode to emit light;
switching on a first transistor coupled across the first electrical input port and the first electrical output port, to provide a relative potential between the first electrical input port and the first electrical output port for stopping the first light emitting diode from emitting light;
switching off the second transistor to stop the discharge of the first capacitor; and switching off the first transistor to terminate the relative potential between the first electrical input port and the first electrical output port of the first light emitting diode.
2. A method according to claim 1 wherein charging of the first capacitor is controlled to provide a known charge on the first capacitor, the known charge constrained in relation to potential thermal damage to the first light emitting diode.
3. A method according to claim 2 wherein the known charge is related to a duration of time during which the first light emitting diode is to continuously emit light.
4. A method according to claim 2 wherein the known charge is related to a frequency of light pulses that the first light emitting diode is to emit.
5. A method according to claim 1 wherein the first transistor is a first MOSFET.
6. A method according to claim 5 wherein the second transistor is a second MOSFET.
7. A method according to claim 1 comprising:
charging a second capacitor; and providing a second pulse of light, comprising the ordered steps of:
switching on a fourth transistor to discharge the second capacitor via a second light emitting diode having a second electrical input port and a second electrical output port, to cause the second light emitting diode to emit light; and switching on a third transistor coupled across the second electrical input port and the second electrical output port, to provide a relative potential between the second electrical input port and the second electrical output port for stopping the second light emitting diode from emitting light;
switching off the fourth transistor to stop the discharge of the second capacitor; and switching off the third transistor to terminate the relative potential between the second electrical input port and the second electrical output port of the second light emitting diode.
charging a second capacitor; and providing a second pulse of light, comprising the ordered steps of:
switching on a fourth transistor to discharge the second capacitor via a second light emitting diode having a second electrical input port and a second electrical output port, to cause the second light emitting diode to emit light; and switching on a third transistor coupled across the second electrical input port and the second electrical output port, to provide a relative potential between the second electrical input port and the second electrical output port for stopping the second light emitting diode from emitting light;
switching off the fourth transistor to stop the discharge of the second capacitor; and switching off the third transistor to terminate the relative potential between the second electrical input port and the second electrical output port of the second light emitting diode.
8. A method according to claim 7 wherein the second capacitor is discharged at a same time as the first capacitor.
9. A method according to claim 7 wherein the second capacitor is discharged in an alternating fashion with the first capacitor.
10. A method according to claim 9 wherein the alternating fashion multiplies a frequency of the pulses of light.
11. A method according to claim 9 wherein the alternating fashion is such that the first pulse of light is emitted followed shortly thereafter by the second pulse of light, the first pulse and the second pulse separated by a time that forms an aperiodic light pulse pattern and other than multiplies a frequency of pulses of light for forming a regular periodic pattern of pulses of light.
12. A method according to claim 9 comprising using a control circuit for independently controlling timing of discharging the first capacitor and discharging the second capacitor to support a first mode of operation wherein the emitted light from the first light emitting diode is summed with the emitted light from the second light emitting diode, a second mode of operation wherein a frequency of light pulses is regular and multiplied by a whole number; and a third mode wherein the emitted light from the first light emitting diode is followed closely in time by the emitted light from the second light emitting diode resulting in a double shot.
13. A method according to claim 1 comprising using a control circuit for controlling timers to switch the first transistor and the second transistor relatively to result in pulses of light emission having known relative start times and known relative end times resulting in light emissions each having a known pulse width.
14. A circuit comprising:
a first light emitting diode have an electrical input port and an electrical output port, the first light emitting diode for emitting light when electrical current flows between the electrical input port and the electrical output port thereof;
a charge storage component for storing charge;
a second switch for switchably releasing the charge via the first light emitting diode to cause light to be emitted therefrom; and a first switch for switching the electrical input port and the electrical output port to a relative potential therebetween, the relative potential for preventing the first light emitting diode from emitting light therefrom.
a first light emitting diode have an electrical input port and an electrical output port, the first light emitting diode for emitting light when electrical current flows between the electrical input port and the electrical output port thereof;
a charge storage component for storing charge;
a second switch for switchably releasing the charge via the first light emitting diode to cause light to be emitted therefrom; and a first switch for switching the electrical input port and the electrical output port to a relative potential therebetween, the relative potential for preventing the first light emitting diode from emitting light therefrom.
15. A circuit according to claim 14 wherein the storage component comprises a first capacitor and comprising a controllable charging circuit for controllably charging the first capacitor to provide a known charge on the first capacitor, the known charge constrained in relation to potential thermal damage to the first light emitting diode.
16. A circuit according to claim 15 wherein the known charge is related to a duration of time during which the first light emitting diode is to continuously emit light.
17. A circuit according to claim 15 wherein the known charge is related to a frequency of light pulses that the first light emitting diode is to emit.
18. A circuit according to claim 14 wherein the first switch comprises a first MOSFET and wherein the second switch comprises a second MOSFET.
19. A circuit according to claim 14 comprising a second light emitting diode disposed in parallel with the first light emitting diode.
20. A circuit according to claim 14 comprising a second light emitting diode disposed in series with the first light emitting diode.
21. A circuit according to claim 14 comprising:
a second light emitting diode have a second electrical input port and a second electrical output port, the second light emitting diode for emitting light when electrical current flows between the second electrical input port and the second electrical output port thereof;
a second storage component for storing second charge;
a fourth switch for switchably releasing the second charge via the second light emitting diode to cause light to be emitted therefrom; and a third switch for switching the electrical input port and the electrical output port to a relative potential therebetween, the relative potential for preventing the second light emitting diode from emitting light therefrom.
a second light emitting diode have a second electrical input port and a second electrical output port, the second light emitting diode for emitting light when electrical current flows between the second electrical input port and the second electrical output port thereof;
a second storage component for storing second charge;
a fourth switch for switchably releasing the second charge via the second light emitting diode to cause light to be emitted therefrom; and a third switch for switching the electrical input port and the electrical output port to a relative potential therebetween, the relative potential for preventing the second light emitting diode from emitting light therefrom.
22. A circuit according to claim 21 wherein the storage component comprises a first capacitor, wherein the second storage component comprises a second capacitor and comprising a control circuit for discharging the second capacitor at a same time as the first capacitor.
23. A circuit according to claim 21 wherein the storage component comprises a first capacitor, wherein the second storage component comprises a second capacitor and comprising a control circuit for discharging the second capacitor in an alternating fashion with the first capacitor.
24. A circuit according to claim 23 wherein the alternating fashion multiplies a frequency of pulses of light.
25. A circuit according to claim 23 wherein the alternating fashion is such that a first pulse of light is emitted followed shortly thereafter by a second pulse of light, the first pulse and the second pulse separated by a time that forms an aperiodic light pulse pattern and other than multiplies a frequency of pulses of light for forming a regular periodic pattern of pulses of light.
26. A circuit according to claim 21 wherein the storage component comprises a first capacitor, wherein the second storage component comprises a second capacitor and comprising a control circuit for independently controlling timing of discharging the first capacitor and discharging the second capacitor to support a first mode of operation wherein the emitted light from the first light emitting diode is summed with the emitted light from the second light emitting diode, a second mode of operation wherein a frequency of light pulses is regular and multiplied by a whole number; and a third mode wherein the emitted light from the first light emitting diode is followed closely in time by the emitted light from the second light emitting diode resulting in a double shot.
27. A method comprising:
charging a first capacitor;
charging a second capacitor;
at intervals of one period, discharging the first capacitor via a first light emitting diode having an electrical input port and an electrical output port to cause the first light emitting diode to emit light; and after a known delay substantially less than one period divided by a number of light emission events per period, discharging the second capacitor via a second light emitting diode having an electrical input port and an electrical output port to cause the second light emitting diode to emit light; and switching a transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the light emitting diode from emitting light.
charging a first capacitor;
charging a second capacitor;
at intervals of one period, discharging the first capacitor via a first light emitting diode having an electrical input port and an electrical output port to cause the first light emitting diode to emit light; and after a known delay substantially less than one period divided by a number of light emission events per period, discharging the second capacitor via a second light emitting diode having an electrical input port and an electrical output port to cause the second light emitting diode to emit light; and switching a transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the light emitting diode from emitting light.
28. A circuit comprising:
a first capacitor;
a second capacitor;
a first light emitting diode having an electrical input port and an electrical output port;
a second light emitting diode having an electrical input port and an electrical output port;
at least a control circuit for controlling charging of the first capacitor and the second capacitor and for at intervals of one period, discharging the first capacitor via the first light emitting diode to cause the first light emitting diode to emit light for forming a light emission event and after a known delay substantially less than one period divided by a number of light emission events from the circuit per period, discharging the second capacitor via the second light emitting diode to cause the second light emitting diode to emit light to form another light emission event;
a first transistor coupled across the electrical input port and the electrical output port of the first light emitting diode to stop the first light emitting diode from emitting light; and a third transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the second light emitting diode from emitting light.
a first capacitor;
a second capacitor;
a first light emitting diode having an electrical input port and an electrical output port;
a second light emitting diode having an electrical input port and an electrical output port;
at least a control circuit for controlling charging of the first capacitor and the second capacitor and for at intervals of one period, discharging the first capacitor via the first light emitting diode to cause the first light emitting diode to emit light for forming a light emission event and after a known delay substantially less than one period divided by a number of light emission events from the circuit per period, discharging the second capacitor via the second light emitting diode to cause the second light emitting diode to emit light to form another light emission event;
a first transistor coupled across the electrical input port and the electrical output port of the first light emitting diode to stop the first light emitting diode from emitting light; and a third transistor coupled across the electrical input port and the electrical output port of the second light emitting diode to stop the second light emitting diode from emitting light.
29. A lighting circuit comprising:
a first light emitting device;
a charge storage component for storing charge; and a control circuit for sensing a voltage across one of the first light emitting device and the charge storage device to provide sensed voltage and , in dependence upon the first light emitting device, feedback current and sensed voltage, automatically controlling a charge voltage on the charge storage component and a duration of a discharge of the charge storage through the first light emitting device.
a first light emitting device;
a charge storage component for storing charge; and a control circuit for sensing a voltage across one of the first light emitting device and the charge storage device to provide sensed voltage and , in dependence upon the first light emitting device, feedback current and sensed voltage, automatically controlling a charge voltage on the charge storage component and a duration of a discharge of the charge storage through the first light emitting device.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2875705A CA2875705C (en) | 2014-12-23 | 2014-12-23 | Method and system for pulsing an led light source |
| CN201510088994.1A CN104703348B (en) | 2014-12-23 | 2015-02-27 | The method and system of pulsed LED light source |
| CN201520117367.1U CN204795688U (en) | 2014-12-23 | 2015-02-27 | Circuit and lighting circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2875705A CA2875705C (en) | 2014-12-23 | 2014-12-23 | Method and system for pulsing an led light source |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2875705A1 CA2875705A1 (en) | 2015-03-04 |
| CA2875705C true CA2875705C (en) | 2015-12-15 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2875705A Active CA2875705C (en) | 2014-12-23 | 2014-12-23 | Method and system for pulsing an led light source |
Country Status (2)
| Country | Link |
|---|---|
| CN (2) | CN104703348B (en) |
| CA (1) | CA2875705C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2875705C (en) * | 2014-12-23 | 2015-12-15 | Ming Zheng | Method and system for pulsing an led light source |
| CN110113847B (en) * | 2019-06-18 | 2021-05-11 | 深圳市卢瑟福科技有限公司 | LED control method and device |
| CN110446312B (en) * | 2019-06-25 | 2022-02-18 | 杭州艾芯智能科技有限公司 | Circuit design method for improving light source performance |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101784142B (en) * | 2009-01-19 | 2013-04-24 | 原景科技股份有限公司 | Light emitting diode circuit with high light-regulating frequency |
| CN102158079B (en) * | 2010-01-26 | 2014-01-29 | 松下电器产业株式会社 | Power source and lighting device |
| CN102271442B (en) * | 2010-06-01 | 2014-07-02 | 登丰微电子股份有限公司 | Driving circuit and control circuit for light emitting diode |
| CN102625534B (en) * | 2012-03-20 | 2015-02-11 | 惠州Tcl移动通信有限公司 | Flash lamp control device for mobile terminal |
| CA2875705C (en) * | 2014-12-23 | 2015-12-15 | Ming Zheng | Method and system for pulsing an led light source |
-
2014
- 2014-12-23 CA CA2875705A patent/CA2875705C/en active Active
-
2015
- 2015-02-27 CN CN201510088994.1A patent/CN104703348B/en active Active
- 2015-02-27 CN CN201520117367.1U patent/CN204795688U/en not_active Withdrawn - After Issue
Also Published As
| Publication number | Publication date |
|---|---|
| CN104703348B (en) | 2017-10-27 |
| CA2875705A1 (en) | 2015-03-04 |
| CN104703348A (en) | 2015-06-10 |
| CN204795688U (en) | 2015-11-18 |
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