Electrical parameter measuring circuit for output signal of LED driver

Abstract

An electrical parameter measuring circuit for an output signal of an LED driver comprises an input end and an output end of the measuring circuit, a current sampling circuit, a switch circuit, a switch driving circuit, a voltage division circuit, a first voltage follower, a second voltage follower, an ADC acquisition circuit, a level conversion circuit, a multiplexing circuit and a single-chip microcomputer. The input end of the measuring circuit is connected with the input end of the voltage division circuit and the current sampling circuit, and the current sampling circuit is connected with the output end of the measuring circuit through the switching circuit. The output end of the voltage division circuit is connected with the input end of the first voltage follower, and the output end of the current sampling circuit is connected with the input end of the second voltage follower and the input end of the level conversion circuit. The input end of the ADC acquisition circuit is connected with the output ends of the first and second voltage followers, and the output end of the ADC acquisition circuit is connected with the single-chip microcomputer. The output end of the level conversion circuit is connected with the single-chip microcomputer through the multiplexing circuit. According to the utility model, various electrical parameters such as direct current and constant current output by the LED driver can be measured.

Description

Technical Field

[0001] The utility model relates to the technology of LED drivers. Background Art

[0002] LEDs have the characteristics of small volume, high brightness, rich color types, pure chromaticity, low power consumption, long service life, etc., and are thus widely used in the automotive field. For example, LEDs are adopted for the headlamps, fog lamps, license plate lamps, reverse lamps, brake lamps, turn signals, position lamps, outline lamps, daytime running lamps, etc. of automobiles.

[0003] The function of an LED driver is to provide a constant current output signal, a PWM signal, etc. to an LED load to drive the LED load to work. At present, there is no measurement circuit in the market that specifically measures the electrical parameters of the output signal of an LED driver. Summary of the Invention

[0004] The technical problem to be solved by the utility model is to provide a measurement circuit for the electrical parameters of the output signal of an LED driver, which can measure various electrical parameters such as the magnitude of the DC constant current output by the LED driver and the duty cycle of the PWM signal for adjusting the brightness of the LED load of the LED driver, and has a simple circuit structure and is easy to implement.

[0005] To solve the above technical problem, the technical solution adopted by the utility model is:

[0006] The electrical parameter measurement circuit for the output signal of an LED driver includes a measurement circuit input terminal, a measurement circuit output terminal, a current sampling circuit, a switching circuit, a switching drive circuit, a voltage dividing circuit, a first voltage follower, a second voltage follower, an ADC acquisition circuit, a level conversion circuit, a multiplexing circuit, and a single-chip microcomputer. The measurement circuit input terminal is used to connect to the signal output terminal of the LED driver. The measurement circuit input terminal is respectively connected to the input terminal of the voltage dividing circuit and the first end of the current sampling circuit. The second end of the current sampling circuit is connected to the first conducting end of the switching circuit. The second conducting end of the switching circuit is connected to the measurement circuit output terminal. The measurement circuit output terminal is used to connect to the LED load. The output terminal of the voltage dividing circuit is connected to the input terminal of the first voltage follower. The output terminal of the current sampling circuit is respectively connected to the input terminal of the second voltage follower and the input terminal of the level conversion circuit. The analog signal input terminals of the ADC acquisition circuit are respectively connected to the output terminal of the first voltage follower and the output terminal of the second voltage follower. The digital signal output terminal of the ADC acquisition circuit is connected to the single-chip microcomputer. The multiplexing circuit has multiple signal input terminals, one signal output terminal, and a control terminal. The output terminal of the level conversion circuit is connected to one of the signal input terminals of the multiplexing circuit. The signal output terminal of the multiplexing circuit is connected to the single-chip microcomputer. The level conversion circuit is used to convert the voltage output by the current sampling circuit into a voltage recognizable by the single-chip microcomputer. The single-chip microcomputer is respectively connected to the control terminal of the multiplexing circuit and the input terminal of the switching drive circuit. The output terminal of the switching drive circuit is connected to the controlled terminal of the switching circuit.

[0007] After adopting the above technical solution, the present utility model has at least the following advantages and characteristics:

[0008] 1. The measurement circuit of the embodiment of the present utility model can measure various electrical parameter values such as the magnitude of the DC constant current output by the LED driver, the voltage drop value of the LED load in the constant current loop, and the duty cycle of the PWM signal for adjusting the brightness of the LED load of the LED driver, making the measurement work more convenient, efficient, and simple, and contributing to realizing automatic measurement and judging whether the working performance of the LED driver meets the design requirements;

[0009] 2. The overall circuit of the present utility model is implemented on a PCBA board, with a simple and compact structure and is easy to implement. Description of the Drawings

[0010] Figure 1 The principle block diagram of the electrical parameter measurement circuit for the output signal of an LED driver according to an embodiment of the present utility model is shown.

[0011] Figure 2 The circuit schematic diagram of the electrical parameter measurement circuit for the output signal of an LED driver according to an embodiment of the present utility model is shown. Detailed Embodiments

[0012] The present utility model will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0013] Figure 1 and Figure 2 shows the circuit principle of the electrical parameter measurement circuit of the LED driver output signal according to an embodiment of the present utility model. Please refer to Figure 1 and Figure 2 . The electrical parameter measurement circuit 100 of the LED driver output signal according to an embodiment of the present utility model includes a measurement circuit input terminal IN, a measurement circuit output terminal OUT, a current sampling circuit 1, a switch circuit 21, a switch driving circuit 22, a voltage dividing circuit 3, a first voltage follower 41, a second voltage follower 42, an ADC acquisition circuit 5, a level conversion circuit 6, a multiplexing circuit 7, and a single-chip microcomputer 8.

[0014] The measurement circuit input terminal IN is used to connect to the signal output terminal of the LED driver 91 to be measured. The measurement circuit input terminal IN is respectively connected to the input terminal of the voltage dividing circuit 3 and the first end of the current sampling circuit 1. The second end of the current sampling circuit 1 is connected to the first conducting end of the switch circuit 21. The second conducting end of the switch circuit 21 is connected to the measurement circuit output terminal OUT. The measurement circuit output terminal OUT is used to connect to the LED load 92. The output terminal of the voltage dividing circuit 3 is connected to the input terminal of the first voltage follower 41. The output terminal of the current sampling circuit 1 is respectively connected to the input terminal of the second voltage follower 42 and the input terminal of the level conversion circuit 6.

[0015] The analog signal input terminals of the ADC acquisition circuit 5 are respectively connected to the output terminal of the first voltage follower 41 and the output terminal of the second voltage follower 42. The digital signal output terminal of the ADC acquisition circuit 5 is connected to the single-chip microcomputer 8. The voltage follower can prevent excessive transient voltages and currents from interfering with and damaging the ADC acquisition circuit 5, and perform impedance conversion on the voltage signal loop output by the voltage dividing circuit 3. Because the voltage follower has an extremely low output impedance (Ro≈0), it can improve the driving ability of the voltage after voltage division.

[0016] The multiplexing circuit 7 has multiple signal input terminals, one signal output terminal, and a control terminal. The input terminal of the level conversion circuit 6 is connected to the output terminal of the current sampling circuit 1. The output terminal of the level conversion circuit 6 is connected to one of the signal input terminals of the multiplexing circuit 7. The signal output terminal of the multiplexing circuit 7 is connected to the single-chip microcomputer 8. The level conversion circuit 6 is used to convert the voltage output by the current sampling circuit 1 into a voltage recognizable by the single-chip microcomputer 8.

[0017] The single-chip microcomputer 8 is respectively connected to the control terminal of the multiplexing circuit 7 and the input terminal of the switch driving circuit 22. The output terminal of the switch driving circuit 22 is connected to the controlled terminal of the switch circuit 21.

[0018] In this embodiment, the current sampling circuit 1 includes a sampling resistor Rs and a current detection amplifier chip U1. The first end and the second end of the sampling resistor Rs respectively form the first end and the second end of the current sampling circuit 1. The first input terminal and the second input terminal of the current detection amplifier chip U1 are respectively connected to the first end and the second end of the sampling resistor Rs, and the output terminal of the current detection amplifier chip U1 forms the output terminal of the current sampling circuit 1. Optionally, the current detection amplifier chip U1 is a current detection amplifier chip with the model number INA240A2DR produced by Texas Instruments. This current detection amplifier chip can accurately measure the current without causing large transients in the output voltage and corresponding recovery ripple. The voltage division circuit 3 includes a resistor R1 and a resistor R2, and the resistor R1 and the resistor R2 are connected in series; the first end of the resistor R1 forms the input terminal of the voltage division circuit 3, the common connection point of the second end of the resistor R1 and the first end of the resistor R2 forms the output terminal of the voltage division circuit 3, and the second end of the resistor R2 is grounded. The models of the first voltage follower 41 and the second voltage follower 42 are LMV321AIDBVR.

[0019] In this embodiment, the ADC acquisition circuit 5 is an analog-to-digital converter with the model number ADS7953 produced by Texas Instruments. This analog-to-digital converter realizes data interaction with the single-chip microcomputer 8 through the SPI bus. The sampling frequency of this analog-to-digital converter is 1 MHz, and it has 16 analog signal input channels. After four processes of sampling, holding, quantization, and encoding, the binary coded data is transmitted to the register of the single-chip microcomputer 8 through the SPI bus. The level conversion circuit 6 is an analog comparator with the model number TLV3201AIDBVT produced by Texas Instruments. The first input terminal of the comparator is connected to the output terminal of the current sampling circuit 1, the second input terminal of the comparator is connected to the reference voltage, and the output terminal of the comparator is connected to one of the signal input terminals of the multiplexing circuit 7; the comparator is used to output a high-level signal when the output voltage of the current sampling circuit 1 is greater than the reference voltage, and output a low-level signal when the output voltage of the current sampling circuit 1 is less than the reference voltage. The multiplexing circuit 7 is a multiplexing switch with the model number ADG706BRUZ produced by Analog Devices. In some specific embodiments, the magnitude of the reference voltage is 0.3 V, the low level is 0 V, and the high level is 3.3 V.

[0020] In this embodiment, the switch circuit 21 is an NMOS transistor, and the gate, drain, and source of the NMOS transistor respectively form the controlled terminal, the first conduction terminal, and the second conduction terminal of the switch circuit 21; the switch driving circuit 22 is an NMOS transistor driving circuit. The NMOS transistor driving circuit 22 is a transistor array driving chip with the model number TBD62083AFWG produced by Toshiba. The single-chip microcomputer 8 is an embedded microcontroller with the model number STM32F427VGT6 produced by STMicroelectronics.

[0021] When measuring the electrical parameters of the output signal of the LED driver 91 using the measurement circuit of this embodiment, connect the input terminal IN of the measurement circuit to the signal output terminal of the LED driver 91, and connect the output terminal OUT of the measurement circuit to the signal input terminal of the LED load 92. In Figure 2 the example of

[0022] When measuring the magnitude of the DC constant current output by the LED driver and the voltage drop value of the LED load in the constant current loop, the signal output terminal of the LED driver 91 outputs a DC constant current (at this time, the PWM modulation circuit Q2 inside the LED driver does not perform modulation). At this time, the single-chip microcomputer 8 controls the switch circuit 21 (NMOS transistor) to conduct through the switch drive circuit 22, and at the same time controls the multiplexing circuit 7 to close (that is, the signal input terminal of the multiplexing circuit 7 is not connected to the signal output terminal). The constant current output by the LED driver 91 flows into the LED load 92 through the sampling resistor Rs (grounded through the entire LED string). The current detection amplifier chip INA240A2DR amplifies the voltage difference generated by the current flowing through the sampling resistor Rs through the internal operational amplifier and outputs a voltage with a fixed gain value. After the voltage signal passes through the second voltage follower 42, it is input to the analog-to-digital conversion channel of the ADC acquisition circuit 5 (that is, used as the current source for measurement). The voltage drop generated by the LED load 92 (that is, the voltage value at the first end of the sampling resistor Rs) is divided by the voltage divider circuit 3 and then output to the first voltage follower 41, and then output to the analog-to-digital conversion channel of the ADC acquisition circuit 5 through the first voltage follower 41 (that is, used as the voltage source for measurement). After the above-mentioned current source and voltage source go through the processes of sampling, holding, quantization, encoding, etc. inside the analog-to-digital converter ADS7953, the converted 12Bits ADC code value is stored in the associated register, and then the data is transmitted to the single-chip microcomputer 8 through its peripheral SPI serial data bus. The single-chip microcomputer 8 obtains the constant current value output by the LED driver and the voltage drop value of the LED load according to the transmitted ADC code value. In other embodiments, the single-chip microcomputer 8 can also obtain 500 or more data within a continuous time period, accumulate them and calculate the average value as the constant current output by the LED driver and the voltage drop value of the LED load.

[0023] When measuring the duty cycle of the PWM signal for adjusting the brightness of the LED load of the LED driver, the signal output terminal of the LED driver 91 outputs a constant current with a certain duty cycle (this duty cycle is the duty cycle of the PWM signal for adjusting the brightness of the LED load) modulated by the PWM modulation circuit Q2 inside the LED driver; at this time, the single-chip microcomputer 8 controls the switch circuit 21 (NMOS transistor) to conduct through the switch drive circuit 22, and at the same time controls the multiplexing circuit 7 to work. The current output by the LED driver 91 flows into the LED load 92 through the sampling resistor Rs (grounded through the entire LED string). The current detection amplifier chip INA240A2DR amplifies the voltage difference generated by the current flowing through the sampling resistor Rs through the internal operational amplifier and outputs a voltage signal with a fixed gain value. The signal is divided into two paths. One path, after passing through the second voltage follower 42, is input to the analog-to-digital conversion channel of the ADC acquisition circuit 5 (since the signal of the duty cycle of the measured PWM signal is finally imported into the single-chip microcomputer for measurement processing through the multiplexing switch, the output signal of the ADC acquisition circuit 5 is ignored). The other path is converted by the level conversion circuit 6 into a PWM signal with the same frequency and a voltage amplitude of 3.3V, and the signal flows into the multiplexing circuit 7 (i.e., the ordinary PWM signal source for measurement). The PWM signal output by the multiplexing circuit 7 enters the PWM acquisition port of the single-chip microcomputer 8. The single-chip microcomputer 8 obtains the pulse width and period of the PWM signal by means of timer timing, and then can obtain the duty cycle of this PWM signal. The aforementioned method of timer timing is an existing technology, which means that when the single-chip microcomputer detects the rising edge of the PWM signal, it triggers the timer to work. After detecting the falling edge of the PWM signal, it records the time between the rising edge and the falling edge (corresponding to the pulse width in the PWM signal). When detecting the next rising edge of the PWM signal, it records the duration of one cycle of the PWM signal. In a specific embodiment, the single-chip microcomputer 8 repeatedly acquires more than 200 groups of data from the multiplexing circuit 7, accumulates them, and calculates the average value as the period value and pulse width value of the PWM output by the LED driver.

[0024] Using the measurement circuit of the embodiment of the present invention can measure various electrical parameter values such as the DC constant current value output by the LED driver, the voltage drop value of the LED load in the constant current loop, and the duty cycle of the PWM signal for adjusting the brightness of the LED load of the LED driver, making the measurement work more convenient, efficient, and simple, and contributing to realizing automatic measurement and judging whether the working performance of the LED driver meets the design requirements.

Claims

1. An electrical parameter measurement circuit for an LED driver output signal, characterized in that: It includes a measuring circuit input terminal, a measuring circuit output terminal, a current sampling circuit, a switch circuit, a switch driving circuit, a voltage dividing circuit, a first voltage follower, a second voltage follower, an ADC acquisition circuit, a level conversion circuit, a multiplexing circuit and a single-chip microcomputer; The input end of the measuring circuit is used to connect to the signal output end of the LED driver, the input end of the measuring circuit is respectively connected to the input end of the voltage divider circuit and the first end of the current sampling circuit, the second end of the current sampling circuit is connected to the first conduction end of the switch circuit, the second conduction end of the switch circuit is connected to the output end of the measuring circuit, and the output end of the measuring circuit is used to connect to the LED load; the output end of the voltage divider circuit is connected to the input end of the first voltage follower, and the output end of the current sampling circuit is respectively connected to the input end of the second voltage follower and the input end of the level conversion circuit; The analog signal input end of the ADC acquisition circuit is connected to the output end of the first voltage follower and the output end of the second voltage follower respectively, and the digital signal output end of the ADC acquisition circuit is connected to the single chip microcomputer; The multiplexing circuit has a plurality of signal input terminals, a signal output terminal and a control terminal; the output terminal of the level conversion circuit is connected to one of the signal input terminals of the multiplexing circuit, the signal output terminal of the multiplexing circuit is connected to the single-chip microcomputer, and the level conversion circuit is used to convert the voltage output by the current sampling circuit into a voltage recognizable by the single-chip microcomputer; The single chip microcomputer is respectively connected to the control end of the multiplexing circuit and the input end of the switch driving circuit, and the output end of the switch driving circuit is connected to the controlled end of the switch circuit.

2. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: The current sampling circuit includes a sampling resistor and a current detection amplifier chip; The first end and the second end of the sampling resistor constitute the first end and the second end of the current sampling circuit respectively; The first input terminal and the second input terminal of the current detection amplifier chip are respectively connected to the first terminal and the second terminal of the sampling resistor, and the output terminal of the current detection amplifier chip constitutes the output terminal of the current sampling circuit.

3. The electrical parameter measurement circuit of the LED driver output signal according to claim 2, characterized in that: The current detection amplifier chip is a current detection amplifier chip of model INA240A2DR produced by Texas Instruments.

4. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: The voltage divider circuit includes a resistor R1 and a resistor R2, wherein the resistor R1 and the resistor R2 are connected in series; the first end of the resistor R1 constitutes the input end of the voltage divider circuit, the common point of the second end of the resistor R1 and the first end of the resistor R2 constitutes the output end of the voltage divider circuit, and the second end of the resistor R2 is grounded.

5. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: Models of the first voltage follower and the second voltage follower are both LMV321AIDBVR.

6. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: The ADC acquisition circuit uses an analog-to-digital converter of model ADS7953 produced by Texas Instruments.

7. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: The switch circuit is an NMOS tube, and the gate, drain and source of the NMOS tube respectively constitute the controlled end, the first conduction end and the second conduction end of the switch circuit; The switch driving circuit is an NMOS tube driving circuit.

8. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: The level conversion circuit includes a comparator, a first input terminal of the comparator is connected to the output terminal of the current sampling circuit, a second input terminal of the comparator is connected to a reference voltage, and an output terminal of the comparator is connected to one of the signal input terminals of the multiplexing circuit; the comparator is used to output a high level signal when the output voltage of the current sampling circuit is greater than the reference voltage, and output a low level signal when the output voltage of the current sampling circuit is less than the reference voltage.

9. The electrical parameter measurement circuit of the LED driver output signal according to claim 1, characterized in that: The multiplexing circuit uses a multiplexing switch of model ADG706BRUZ produced by Analog Devices.

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