CN112333888A - Multi-constant-current-driven LED and LD open-circuit fault detection circuit and detection method - Google Patents

Multi-constant-current-driven LED and LD open-circuit fault detection circuit and detection method Download PDF

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CN112333888A
CN112333888A CN202011318150.9A CN202011318150A CN112333888A CN 112333888 A CN112333888 A CN 112333888A CN 202011318150 A CN202011318150 A CN 202011318150A CN 112333888 A CN112333888 A CN 112333888A
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circuit
voltage
led
digital
constant current
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CN112333888B (en
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赵翔
洪普
项青
郭磊
杨兴
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Hubei Jiuzhiyang Infrared System Co Ltd
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Hubei Jiuzhiyang Infrared System Co Ltd
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    • 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]
    • H05B45/30—Driver circuits
    • H05B45/345—Current stabilisation; Maintaining constant current
    • 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]
    • H05B45/30—Driver circuits
    • H05B45/32—Pulse-control circuits
    • H05B45/325—Pulse-width modulation [PWM]
    • 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]
    • H05B45/30—Driver circuits
    • H05B45/36—Circuits for reducing or suppressing harmonics, ripples or electromagnetic interferences [EMI]
    • 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]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • 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
    • H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
    • H05B47/10—Controlling the light source
    • H05B47/165—Controlling the light source following a pre-assigned programmed sequence; Logic control [LC]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

The invention discloses a multi-constant current driven LED and LD open circuit fault detection circuit and a detection method, wherein the detection circuit comprises: the circuit comprises a front-end current signal extraction circuit, a reference voltage generation circuit, a voltage comparison circuit, a pulse signal acquisition and processing circuit and an open-circuit fault alarm circuit. The open-circuit fault detection circuit and the detection method for the LED and the LD driven by multiple constant currents do not depend on a specific driving power supply topological form, can be suitable for various LED/LD constant-current driving topological forms, are suitable for a single LED/LD, a single LED/LD serial and a multiple LED/LD serial (as long as the driving power supplies of the serials are grounded), are suitable for the LED/LD driven by multiple constant currents and the LED/LD driven by single constant current, and have excellent universality; and by adopting the digital programmable device, the flexibility, configurability and functional expandability of the whole circuit are greatly improved.

Description

Multi-constant-current-driven LED and LD open-circuit fault detection circuit and detection method
Technical Field
The invention belongs to the technical field of circuits, and particularly relates to a multi-constant-current-driven LED and LD open-circuit fault detection circuit and a detection method.
Background
LEDs have been replacing conventional lighting devices in more and more fields due to their outstanding advantages of high brightness, high luminous efficiency, long lifetime, etc. In the outdoor places such as airport navigation aid, railway signal lamps, road traffic lights and the like which take the LED as a lighting or indicating light source, the LED is required to reliably run under the unattended condition, so that whether the LED (or the serial thereof) is in a normal constant current working state or an open-circuit fault state or not is required to be detected in real time during specific application. In addition, in the case where constant current driving is required similarly to a laser diode pumped solid-state laser, a laser dazzler, or the like, since a laser diode is required to have a sealing process and an environment, it is also required to be able to electrically detect whether an LD (or its single-string/multiple-string) is in a normal constant current driving state or an open circuit state in real time.
The LED dimming mode under the power supply of the direct current power supply mostly adopts PWM dimming with fixed frequency; for the LD-pumped solid-state laser, a pulse mode with variable frequency and fixed pulse width is generally used for driving; there are also operating modes that use a continuous constant current to directly drive the LD to emit a laser for glare or target indication. However, in any operation mode, or in any case of using the LED or the LD, the constant driving current may be adjusted according to actual requirements to change the light emitting intensity of the LED or the emitting energy of the LD.
The invention discloses a light emitting diode and laser diode open circuit fault detection circuit in Chinese patent CN104507243B, provides a general LED/LD open circuit fault detection circuit, and solves the problem that open circuit faults are not convenient to detect through a circuit output end voltage abnormity mode by Buck topology constant current driving, linear constant current driving and the like. However, when the constant current driving the LED/LD changes, the differential amplifier generally does not have a gain-adjustable function, so the circuit cannot adjust the high/low level voltage value required for the output voltage of the differential amplifier to the input terminal of the xor gate, that is, the circuit does not have the LED/LD open circuit fault detection function under the condition of multiple constant current driving. In addition, once the circuit catches the occurrence of an open-circuit fault event, the circuit can always output a fault alarm action, even if the LED/LD driving circuit is recovered to be normal, and therefore judgment on the authenticity of the fault alarm can be influenced.
Disclosure of Invention
The invention aims to provide a multi-constant current driven LED and LD open circuit fault detection circuit and a detection method, and solves the problem of LED/LD open circuit fault detection under the condition of multi-constant current driving.
The invention provides a multi-constant current driven LED and LD open circuit fault detection circuit, comprising:
the front-end current signal extraction circuit comprises a sampling resistor and a differential amplifier; the sampling resistor is connected with the LED/LD in series; the two input ends of the differential amplifier are connected with the two ends of the sampling resistor, and the output end of the differential amplifier outputs a voltage proportional to the voltage at the two ends of the sampling resistor;
the reference voltage generating circuit comprises a digital programmable device, a bus isolator and a digital-to-analog converter; the digital programmable device is used for acquiring constant current driving information of the LED/LD, and is connected with the bus isolator through the bus interface, the bus isolator is connected with the digital-to-analog converter, and the output end of the digital-to-analog converter outputs analog voltage with variable amplitude;
a voltage comparison circuit comprising a voltage comparator; two input ends of the voltage comparator are respectively connected with the output end of the differential amplifier and the output end of the digital-to-analog converter, and the output end of the voltage comparator outputs high or low level voltage;
the pulse signal acquisition and processing circuit comprises a digital programmable device; the digital programmable device is used for carrying out time delay processing on the jump edge of the dimming PWM signal of the LED or the pulse driving signal of the LD, interpreting the voltage output by the voltage comparator after the time of the delayed jump edge, and determining whether to give an alarm or not according to the interpretation result;
and the open-circuit fault alarm circuit is used for outputting alarm signals and information.
Furthermore, the jump edge delay amount of the dimming PWM signal of the LED or the pulse driving signal of the LD is larger than the sum of the delay amount of the constant driving circuit, the delay amount of the differential voltage signal processed by the differential amplifier and the delay amount of the analog signal processed by the voltage comparison circuit.
Further, the digital programmable device can acquire the driving current size information required by the LED/LD, and accordingly adjust the output voltage value of the analog-to-digital converter through the bus isolator.
Furthermore, the voltage comparison circuit also comprises a first resistor and a second resistor, wherein the first resistor is connected with the output end of the differential amplifier and the non-inverting input end of the voltage comparator, and the second resistor is connected with the output end of the voltage comparator and the non-inverting input end of the voltage comparator, so that a circuit with a hysteresis comparison function is formed, the voltage comparison circuit has certain anti-interference capability, and high and low levels which are not easy to turn over can be output under a certain electromagnetic interference environment.
Furthermore, the high and low input voltage thresholds of the hysteresis voltage comparison circuit are both smaller than the voltage amplitude output by the differential amplifier under the condition of no open-circuit fault.
Further, the voltage output by the differential amplifier is in an in-phase proportion or an anti-phase proportion relation with the voltage drop of the two ends of the sampling resistor.
Furthermore, the pulse signal acquisition and processing circuit also comprises a first level isolator, and the dimming PWM signal of the LED or the pulse driving signal of the LD is transmitted to the digital programmable device through the first level isolator.
Furthermore, the voltage comparison circuit also comprises a second level isolator, and the second level isolator is connected with the output end of the voltage comparison circuit and the digital programmable device.
Further, the open-circuit fault alarm circuit comprises a local alarm device, and the local alarm device is an alarm lamp or a buzzer.
Furthermore, the open-circuit fault alarm circuit comprises a remote uploading circuit, and the remote uploading circuit uploads the alarm information to the remote equipment through a serial communication interface of the digital programmable device and an external bus.
The invention also provides a multi-constant current driven LED and LD open circuit fault detection method, which comprises the following steps:
connecting a sampling resistor with an LED/LD in series, collecting voltages at two ends of the sampling resistor by using a differential amplifier, and outputting a voltage proportional to the voltage;
the digital programmable device outputs analog voltage with variable amplitude by using a digital-to-analog converter according to the information of the constant current for driving the LED/LD;
comparing the voltage output by the differential amplifier with the analog voltage output by the digital-to-analog converter by using a voltage comparator, and outputting a comparison voltage;
the digital programmable device acquires a dimming PWM signal of an LED or a pulse driving signal of an LD and carries out jump edge delay processing;
and the digital programmable device judges the comparison voltage output by the voltage comparator after the delayed jump edge moment and determines whether to alarm or not according to the judgment result.
The invention has the beneficial effects that: the open-circuit fault detection circuit and the detection method for the LED and the LD driven by multiple constant currents do not depend on a specific driving power supply topological form, can be suitable for various LED/LD constant-current driving topological forms, are suitable for a single LED/LD, a single LED/LD serial and a multiple LED/LD serial (as long as the driving power supplies of the serials are grounded), are suitable for the LED/LD driven by multiple constant currents and the LED/LD driven by single constant current, and have excellent universality; and by adopting the digital programmable device, the flexibility, configurability and functional expandability of the whole circuit are greatly improved. And when the LED/LD driving circuit returns to normal, the alarm is stopped, so that the judgment on the authenticity of the fault alarm is not influenced.
Drawings
FIG. 1 is a functional block diagram of the multiple constant current driven LED and LD open circuit fault detection circuit of the present invention;
FIGS. 2A and 2B are circuit diagrams of a preferred embodiment of the present invention; fig. 2A is a diagram of a pulse signal acquisition and processing circuit and an open-circuit fault alarm circuit, and fig. 2B is a diagram of a front-end current signal extraction circuit, a reference voltage generation circuit and a voltage comparison circuit;
FIG. 3 is a flowchart of a process used by a microcontroller in an embodiment of the present invention;
FIG. 4 is a timing diagram of some key signals in an embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings in which:
the invention provides a circuit and a detection method capable of detecting an open-circuit fault of an LED/LD (light-emitting diode/LD) in real time under the condition of adopting a power supply in any topological form and driving the LED/LD by multiple constant currents (naturally, the LED/LD also comprises single constant current driving). The present invention is applied to an open fault detection circuit of an LED/LD by way of example, but it should be appreciated that a circuit such as a dc adjustable speed motor current abnormality detection can be constructed using the present invention, so the present invention has a wider application range.
The multiple constant current driven LED and LD open circuit fault detection circuit of the embodiment of the invention comprises:
the front-end current signal extraction circuit comprises a sampling resistor and a differential amplifier; the sampling resistor is connected with the LED/LD in series; the two input ends of the differential amplifier are connected with the two ends of the sampling resistor, and the output end of the differential amplifier outputs the extracted voltage. The front-end current signal extraction circuit is configured to bear enough common-mode input voltage, and a differential amplifier DOPA with a certain differential mode signal processing speed is used for extracting the potential difference between two ends of the current acquisition resistor, and the potential difference is output to be a voltage signal or a pulse voltage signal with certain load capacity through the differential amplifier, and the signal represents whether constant current passes through the LED/LD or not. The current sampling resistor is connected in series with the LED/LD and the enabling switch thereof, namely the current of the LED/LD can be collected in real time, so that the resistor is not fixed at a certain specific position in the circuit. The extracted voltage output by the differential amplifier and the voltage drop at two ends of the sampling resistor are in the same phase proportion or reverse phase proportion relation, namely the input polarity of the differential amplifier can be consistent with the current direction or opposite, and the reference point position can be selected or selected as an external voltage reference.
The reference voltage generating circuit comprises a digital programmable device, a bus isolator and a digital-to-analog converter; the digital programmable device is used for acquiring constant current driving information of the LED/LD, and is connected with the bus isolator through the bus interface, the bus isolator is connected with the digital-to-analog converter, and the output end of the digital-to-analog converter outputs analog voltage with variable amplitude. The bus isolator can correctly receive and transmit signals on a corresponding bus and has a certain level of voltage isolation function. And the reference voltage generating circuit is configured to acquire constant current intensity information or constant current switching information which the current driving LED/LD should have by using a digital programmable device so as to set and adjust the output voltage of the digital-to-analog converter according to the constant current intensity information or the constant current switching information. The digital programmable device, such as DPD, can send a command to the DAC through its on-chip component level bus interface OCDI and bus isolator BISO, thereby driving the DAC to output an analog voltage with a variable amplitude for subsequent comparison.
A voltage comparison circuit comprising a voltage comparator; two input ends of the voltage comparator are respectively connected with the output end of the differential amplifier and the output end of the digital-to-analog converter, and the output end of the voltage comparator outputs comparison voltage. A voltage comparison circuit configured to input the output voltage of the differential amplifier DOPA and the output voltage of the digital-to-analog converter DAC to the voltage comparator VCMP, thereby obtaining a high level or a low level at an output terminal of the voltage comparator.
The pulse signal acquisition and processing circuit comprises a digital programmable device; the digital programmable device is used for carrying out time delay processing on the jump edge of the dimming PWM signal of the LED or the pulse driving signal of the LD, interpreting the output of the voltage comparator after the time of the delayed jump edge, and determining whether to alarm or not according to the interpretation result. The pulse signal acquisition and processing circuit is configured to input a PWM dimming signal or a driving signal for driving the LED/LD to a general digital port GPIOa of the DPD through the first level isolator DISO1, and then the DPD performs delay processing on a transition edge of the pulse, so that the voltage comparison circuit interprets a high-low level signal output to the digital port XINT by the second level isolator DISO2 after the delayed transition edge.
After the digital programmable device receives the dimming PWM signal or the pulse driving signal, certain time delay is carried out on a pulse jumping edge through an on-chip program, and a delayed rising edge and a non-delayed falling edge are taken as time boundaries, so that whether the LED/LD has an open-circuit fault or not is judged according to a high-low level signal received by XINT in the time period. The level information which is output by the voltage comparison circuit and is isolated by the second level isolator and is clamped between the delayed pulse rising edge and the undelayed pulse falling edge is mainly read. Furthermore, the jump edge delay amount of the dimming PWM signal of the LED or the pulse driving signal of the LD is larger than the sum of the delay amount of the constant current driving circuit, the delay amount of the differential voltage signal processed by the differential amplifier and the delay amount of the analog signal processed by the voltage comparison circuit.
The PWM dimming signal or the pulse driving signal of the LD is a signal for enabling the LED/LD to be turned on, that is, when the PWM dimming signal or the pulse driving signal of the LD is at a high (low) level, if the relevant constant current driving circuit operates normally and no open circuit fault occurs, there is a normal current passing through the LED/LD, and the delay of the rising (falling) edge of the current with respect to the rising (falling) edge of the PWM dimming signal or the pulse driving signal is sufficiently short. The PWM dimming signal/pulse driving signal is transmitted to the constant current driving circuit to serve as an LED/LD driving enabling signal, and is received by a universal digital port of the digital programmable device and delayed, so that whether an open-circuit fault occurs or not is judged by reading the high and low levels output by the hysteresis voltage comparison circuit between the rising edge and the undelayed falling edge of the delayed pulse signals.
And the open-circuit fault alarm circuit is used for alarming. The open-circuit fault alarm circuit is configured in such a way that the DPD drives a local alarm device to visually indicate an open-circuit fault in the forms of sound, light, electricity and the like through GPIob according to the level state received by the interpretation XINT, wherein the local alarm device is an alarm lamp or a buzzer and the like; the open-circuit fault alarm circuit can also comprise a remote uploading circuit, for example, alarm information is sent to an upper computer by using a serial communication interface SCI and an external bus through a DPD (digital pre-distortion) so as to transmit an open-circuit fault message to a remote device.
Furthermore, the voltage comparison circuit further comprises a first resistor and a second resistor, the first resistor is connected with the output end of the differential amplifier and the non-inverting input end of the voltage comparator, and the second resistor is connected with the output end of the voltage comparator and the non-inverting input end of the voltage comparator. The peripheral circuit with the hysteresis comparison function formed by the first resistor and the second resistor enables the voltage comparison circuit to have the hysteresis voltage comparison function, and enables the circuit to have certain anti-jamming capability: the voltage comparator can receive the output voltage of the differential amplifier without error turnover of the output level thereof under a certain electromagnetic interference environment; and when the LED/LD is switched in normal constant driving current from no driving current, the output high-low voltage can be inverted, and the output high-low voltage is transmitted to a digital input port of the digital programmable device through the level isolator. The high and low input voltage threshold values of the hysteresis voltage comparison circuit are both smaller than the voltage amplitude value output by the differential amplifier under the condition of no open-circuit fault.
Furthermore, the pulse signal acquisition and processing circuit also comprises a first level isolator, and the dimming PWM signal of the LED or the pulse driving signal of the LD is transmitted to the digital programmable device through the first level isolator. The voltage comparison circuit further comprises a second level isolator, and the second level isolator is connected with the output end of the voltage comparison circuit and the digital programmable device. The digital programmable device can receive high and low level signals output by the voltage comparison circuit through the second level isolator. The corresponding level isolator can convert high and low voltage signals on the side of the driving power supply ground into high and low level signals on the side of the digital ground, and has a certain level of voltage isolation function.
The present invention also provides a preferred embodiment of a multiple constant current driven LED and LD open circuit fault detection circuit, as shown in fig. 1, comprising: the circuit comprises a front-end constant-current signal extraction circuit 100, a digital programmable circuit 200, a digital-to-analog conversion circuit 300, a hysteresis voltage comparison circuit 400 and a local and remote fault alarm circuit 500.
The front-end constant current signal extraction circuit 100 comprises a differential amplifier and a current sampling resistor connected in series in the LED/LD constant current driving circuit. The differential amplifier can extract the potential difference between two ends of the current sampling resistor under the environment of higher common-mode voltage and amplify the potential difference to a certain degree. Since the input polarity of the differential amplifier can be either the same as or opposite to the current direction, and the reference point can be selected either from the reference point or the external voltage reference, the components in the front-end voltage signal extraction and processing circuit 100 can be implemented in various forms and different devices. In the embodiment shown in fig. 2B, the differential amplifier AD8418A amplifies the output voltage signal sgn1 and the current sampling resistor R under the premise that the reference potential is groundedSThe voltage drop (parallel connection of two 0.62 Ω resistors) is in phase and 20 times proportional.
The digitally programmable circuit 200 includes three sets of input signals/information and three sets of output signals/information, in accordance with the direction of signal flow to the outside. The three sets of input signals/information are:
leading to a dimming PWM signal/pulse signal sgn2 of a general purpose digital port GPIOa through a digital level isolator DISO 1;
signal sgn4 output by the hysteresis voltage comparison circuit and transmitted to the digital input port XINT through the digital level isolator DISO 2;
and the LED/LD constant driving current switching information (signal).
The three sets of output signals/information are:
firstly, according to the constant driving current information (signal) which the LED/LD should have at present, an instruction for adjusting the output analog voltage sgn3 is sent to a digital-to-analog converter DAC through an element level bus and an isolator BISO thereof;
judging the received sgn4 signal to send out the alarm signal whether to drive relative sound, light and electricity to the local alarm device LWU;
and sending related open-circuit fault information or normal operation information to a remote upper computer through an external bus.
In the embodiment shown in fig. 2B, since the pulse current signal formed by the LED constant current driving circuit on Rs has a certain delay function with respect to the dimming PWM signal, and the differential amplifier AD8418A and the voltage comparator TLV3201 also have a delay function in processing the analog signal, the rising edge of the signal sgn2 needs to be delayed by the microcontroller C8051F330, so that the microcontroller only processes the signal sent to the digital input port XINT (i.e., pin P0.0) between the delayed rising edge and the undelayed falling edge, and thus the C8051F330 can correctly determine whether there is an open circuit fault of the LED/LD in timing.
The digital-to-analog conversion circuit 300 includes a digital-to-analog converter DAC and an isolator BISO capable of isolating and transceiving on-chip bus information. On the one hand, through the chip-level bus and the isolator thereof, the digital programmable device DPD sends an instruction to adjust the analog voltage sgn3 to the DAC according to the current driving constant current information that the digital programmable device DPD should obtain for the LED/LD, thereby setting one input end of the voltage comparator. On the other hand, the signal sgn1 output by the front-end constant-current signal extraction circuit 100 sets the other input terminal of the voltage comparator. In the embodiment shown in fig. 2A, when the general digital port GPIOc (i.e. pin P1.4) of C8051F330 obtains a high level signal, the driving current of the current LED string should be 350mA, so as to issue a command to AD5683R to set its analog voltage output to 1.7727V through the SPI bus and its isolator ADuM 1411; when the GPIOc of the general-purpose digital port gpio of C8051F330 receives a low signal, it indicates that the current driving current of the LED string should be 700mA, so that an instruction to set the analog voltage output to 3.7727V is sent to the AD5683R through the SPI bus and the isolator thereof ADuM 1411.
The hysteresis voltage comparator circuit 400 includes a voltage comparator and peripheral circuits that can form a hysteresis comparison function. Under the action of the hysteresis comparison circuit, the voltage comparator can output high and low levels which are not easy to overturn by mistake in a certain electromagnetic interference environment. In the embodiment shown in FIG. 2B, two resistors R are provided around the voltage comparator TLV3201(+5V supply)7(30 k.OMEGA.) and R8(300k omega) so that the in-phase hysteresis voltage comparison capability of 0.5V is provided. When the driving current of the LED string is 350mA, the high and low input threshold voltages are 1.950V and 1.450V respectively; when the driving current of the LED string is equal toAt 700mA, the high and low input threshold voltages are 4.150V and 3.650V respectively. Therefore, if the LED string normally passes the 350mA or 700mA driving current, the AD8418A will output 4.34V or 2.17V, respectively, thereby making the TLV3201 output high (slightly lower than + 5V); and when no current flows through the LED string or an open circuit fault occurs, the TLV3201 is made to output a low level (slightly higher than 0V). After C8051F330 delays the rising edge of sgn2 by a certain amount, external interrupt XINT (configured by the on-chip program as a falling edge trigger) should be turned on as shown in fig. 3; and when the falling edge of sgn2 comes, external interrupt XINT is disabled. That is, the program within the microcontroller chip can completely distinguish whether the XINT port is low due to an open failure of the LED string or due to a low period of the dimming PWM signal.
The local and remote fault alarm circuit 500 includes a local fault alarm circuit and a remote fault alarm circuit connected to the upper computer through an external bus. In the embodiment shown in fig. 2A, if the DPD reads out a low level of sgn4 signal between the rising edge of sgn2 delayed and the falling edge of sgn2 not delayed, GPIOb (i.e., P1.5 pin) outputs a current for driving the buzzer, and calls the UART unit in the DPD chip to send out a fault message to the upper computer through the RS422 bus.
FIG. 4 is a timing diagram of some key signals in an embodiment of the invention, in which: note 1 indicates the time period for which the rising edge of the pulse signal is delayed in the PCA0 interrupt service routine; note 2 represents the hysteresis comparison circuit high threshold voltage set at 700mA drive current; note 3 represents the DAC output voltage set at 700mA drive current; note 4 represents the hysteresis comparison circuit low threshold voltage set at 700mA drive current; note 5 represents the hysteresis comparison circuit high threshold voltage set at 350mA drive current; note 6 represents the DAC output voltage set at 350mA drive current; note 7 represents the hysteresis comparison circuit low threshold voltage set at 350mA drive current.
The invention also provides a method for detecting open-circuit faults of LEDs and LDs by utilizing the circuit to drive multiple constant currents, which comprises the following steps:
connecting a sampling resistor with the LED/LD in series, and collecting voltages at two ends of the sampling resistor by using a differential amplifier;
according to the constant current driving information of the LED/LD, outputting analog voltage with variable amplitude by using a digital-to-analog converter;
comparing the voltage at two ends of the sampling resistor with the analog voltage by using a voltage comparator, and outputting a comparison voltage;
acquiring a dimming PWM signal of an LED or a pulse driving signal of an LD, and performing jump edge delay processing;
and judging the voltage output by the voltage comparator after the time of the delayed jump edge, and determining whether to alarm or not according to the judgment result.
In summary, the circuit of the present invention does not depend on a specific driving power topology, and is applicable as long as it can drive the LED/LD with a constant current; the hysteresis voltage comparison circuit adopted in the circuit has certain anti-jamming capability and can work under the complex electromagnetic environment conditions of an LED/LD constant current source driven by a switching power supply and the like; the working condition of the LED/LD can be detected in real time under a higher common mode voltage environment, and the LED/LD is digitally isolated from a driving circuit of the LED/LD, so that the LED/LD has better electromagnetic compatibility and man-machine safety; the digital programmable device of the circuit has the characteristics of expandable function and flexible configuration, namely the device can be used for detecting open-circuit faults and can also be fully developed, so that the device has the capabilities of power management, real-time monitoring of various environmental parameters and the like; if the MCU is adopted as a digital programmable device, the digital programmable device also has the advantages of low power consumption, low cost and high product development speed.
It will be understood by those skilled in the art that the foregoing is merely a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included within the scope of the present invention.

Claims (10)

1. A multiple constant current driven LED and LD open circuit fault detection circuit, comprising:
the front-end current signal extraction circuit comprises a sampling resistor and a differential amplifier; the sampling resistor is connected with the LED/LD in series; the two input ends of the differential amplifier are connected with the two ends of the sampling resistor, and the output end of the differential amplifier outputs a voltage proportional to the voltage at the two ends of the sampling resistor;
the reference voltage generating circuit comprises a digital programmable device, a bus isolator and a digital-to-analog converter; the digital programmable device is used for acquiring constant driving current information required by the LED/LD, and is connected with the bus isolator through the bus interface, the bus isolator is connected with the digital-to-analog converter, and the output end of the digital-to-analog converter outputs analog voltage with variable amplitude;
a voltage comparison circuit comprising a voltage comparator; two input ends of the voltage comparator are respectively connected with the output end of the differential amplifier and the output end of the digital-to-analog converter, and the output end of the voltage comparator outputs high or low level voltage;
the pulse signal acquisition and processing circuit comprises a digital programmable device; the digital programmable device is used for carrying out time delay processing on the jump edge of the dimming PWM signal of the LED or the pulse driving signal of the LD, interpreting the voltage output by the voltage comparator after the time of the delayed jump edge, and determining whether to give an alarm or not according to the interpretation result;
and the open-circuit fault alarm circuit is used for outputting alarm signals and information.
2. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 1, wherein the transition edge delay amount of the dimming PWM signal of the LED or the pulse driving signal of the LD is greater than the sum of the delay amount of the constant driving circuit, the delay amount of the differential amplifier processing the differential voltage signal, and the delay amount of the voltage comparison circuit processing the analog signal.
3. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 1, wherein the voltage comparison circuit further comprises a first resistor and a second resistor, the first resistor connecting the output of the differential amplifier and the non-inverting input of the voltage comparator, the second resistor connecting the output of the voltage comparator and the non-inverting input of the voltage comparator, forming a hysteretic voltage comparison circuit.
4. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 3, wherein the high and low input voltage thresholds of the hysteretic voltage comparison circuit are both less than the magnitude of the voltage output by the differential amplifier without an open circuit fault.
5. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 1, wherein the voltage output by the differential amplifier is proportional in phase or in anti-phase to the voltage drop across the sampling resistor.
6. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 1, wherein the pulse signal collection and processing circuit further comprises a first level isolator through which the dimming PWM signal of the LED or the pulse drive signal of the LD is transferred to the digital programmable device.
7. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 1, wherein the voltage comparison circuit further comprises a second level isolator connecting the output of the voltage comparison circuit and the digital programmable device.
8. The multiple constant current driven LED and LD open circuit fault detection circuit according to claim 1, wherein the open circuit fault alarm circuit includes a local alarm device, the local alarm device being an alarm lamp or a buzzer.
9. The multiple constant current driven LED and LD open circuit fault detection circuit of claim 1, wherein the open circuit fault alarm circuit includes a remote upload circuit that uploads alarm information to a remote device via a serial communication interface of a digital programmable device and an external bus.
10. A multi-constant current driven LED and LD open circuit fault detection method is characterized by comprising the following steps:
connecting a sampling resistor with an LED/LD in series, collecting voltages at two ends of the sampling resistor by using a differential amplifier, and outputting a voltage proportional to the voltage;
the digital programmable device outputs analog voltage with variable amplitude by using a digital-to-analog converter according to the information of the constant current for driving the LED/LD;
comparing the voltage output by the differential amplifier with the analog voltage output by the digital-to-analog converter by using a voltage comparator, and outputting a comparison voltage;
the digital programmable device acquires a dimming PWM signal of an LED or a pulse driving signal of an LD and carries out jump edge delay processing;
and the digital programmable device judges the comparison voltage output by the voltage comparator after the delayed jump edge moment and determines whether to alarm or not according to the judgment result.
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