PWM dimming circuit

Abstract

The utility model belongs to the technical field of airborne lighting, and particularly discloses a PWM dimming circuit which comprises an MCU main control circuit, a crystal oscillator, an LDO power supply circuit, a voltage follower circuit, a PWM output circuit and a connection relation thereof. According to the utility model, the PWM output circuit is arranged to output two PWM waveforms with different amplitudes according to requirements, the light modulation range of 200HZ-2KHZ is provided, and the light modulation requirements of most airborne lighting systems are met; the voltage follower circuit is adopted to acquire voltage, input impedance is high, and acquisition is accurate.

Description

TECHNICAL FIELD

[0001] The utility model relates to airborne lighting technical field, especially a kind of PWM dimming circuit. BACKGROUND

[0002] PWM dimming is a kind of power, but a certain frequency in very short time, to luminous body (such as LED) is carried out " bright → extinguish → bright → extinguish " alternation, through adjusting the time proportion of " bright " and " extinguish ", the brightness adjustment method from dark to bright. From market prospect, the prospect of PWM dimming technology is positive. PWM dimming technology is widely considered as one of the best dimming schemes because of its smooth dimming effect and no color spectrum deviation. With the continuous progress of LED lighting technology, PWM dimming technology is also used in airborne lighting field. Considering the working environment of airborne product, it is necessary to design a PWM dimming module that can meet the requirements and has high generalization degree.

[0003] There are many schemes that can be used for PWM dimming at present, among which the most common is microcontroller device;There are also low-cost schemes, such as timer chip. The main advantages of microcontroller scheme are high precision and less affected by environment. However, there are many schemes at present, and there is no standardized scheme, which is not conducive to reliability and cost control. Some oscillator chips mainly rely on peripheral circuit to determine frequency, although it is simple to use, but the cost is low, but it is greatly affected by environmental temperature, when the environmental temperature changes greatly, it is easy to produce frequency deviation, which does not meet the characteristics of airborne use.

[0004] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the utility model, and therefore can include information that does not constitute prior art known by those skilled in the art. CONTENT OF UTILITY MODEL

[0005] The utility model aims at solving the technical problems in the background art, and provides a PWM dimming circuit.

[0006] In order to achieve the above purpose, the utility model adopts the following technical scheme:

[0007] A kind of PWM dimming circuit, including MCU main control circuit, LDO power supply circuit, voltage follower circuit and PWM output circuit;

[0008] The LDO power supply circuit is electrically connected with MCU main control circuit and PWM output circuit;

[0009] The LDO power supply circuit is electrically connected with voltage follower circuit, and the voltage follower circuit is electrically connected with MCU main control circuit;

[0010] The MCU master circuit is electrically connected with the PWM output circuit.

[0011] The LDO power supply circuit comprises an LD1 high-voltage power supply circuit and an LD2 low-voltage power supply circuit connected in series.

[0012] The PWM output circuit comprises a selection switch, a pull-up resistor R15, a pull-up resistor R25 and a transistor Q1, the output end of the LD1 high-voltage power supply circuit is electrically connected with the input end one of the selection switch through the pull-up resistor R15, the output end of the LD2 low-voltage power supply circuit is electrically connected with the input end two of the selection switch through the pull-up resistor R25, and the output end of the selection switch is electrically connected with the collector of the transistor Q1.

[0013] The PWM output circuit further comprises resistors R16 and R17, the resistor R17 is connected between the base and the emitter of the transistor Q1, the base of the transistor Q1 is electrically connected with one end of the resistor R16, the other end of the resistor R16 is electrically connected with the MCU master circuit, and the collector of the transistor Q1 is used as a PWM output port and is connected with an external connector H2.

[0014] The MCU master circuit is electrically connected with the PWM output circuit.

[0015] The LDO power supply circuit comprises a linear voltage stabilizer U6 and a linear voltage stabilizer U7, an external power supply is connected with the VIN end of the linear voltage stabilizer U6, the VIN end and the GND end of the linear voltage stabilizer U6 are connected with a capacitor C2, the GND end of the linear voltage stabilizer U6 is grounded, the VOUT end of the linear voltage stabilizer U6 is grounded through a capacitor C12, the VOUT end of the linear voltage stabilizer U6 is connected with the VIN end of the linear voltage stabilizer U7, the VIN end and the GND end of the linear voltage stabilizer U7 are connected with a capacitor C13, and the VOUT end of the linear voltage stabilizer U7 is grounded through a capacitor C3.

[0016] The voltage follower circuit comprises an operational amplifier U2, one power pin of the operational amplifier U2 is connected with the VOUT end of the linear voltage stabilizer U6, and the other power pin is grounded; the two power pins of the operational amplifier U2 are connected with a capacitor C5, the output end and the inverting input end of the operational amplifier U2 are connected and grounded through a resistor R1 and a stabilizing tube D1, and the circuit between the resistor R1 and the stabilizing tube D1 is connected to the MCU master circuit.

[0017] The utility model further limits the technical scheme, the positive phase input end of operational amplifier U2 is connected the external connector H3 through resistance R2, R3, R4 and electric capacity C6, wherein, electric capacity C6 one end with the positive phase input end of operational amplifier U2, the other end ground connection;Resistance R2, R3 are connected between the positive phase input end of operational amplifier U2 and the external connector H3;Resistance R4 one end is connected on the line between resistance R2, R3, the other end ground connection.

[0018] The utility model further limits the technical scheme, the voltage follower circuit still includes resistance R18, R19, R20, R21, R22, R23;

[0019] Resistance R18 one end is connected with the VOUT end of linear voltage stabilizer U7, the other end is connected with MCU main control circuit through resistance R21, the pin 2 of external connector H3 is connected on the line between resistance R18 and resistance R21;

[0020] Resistance R19 one end is connected with the VOUT end of linear voltage stabilizer U7, the other end is connected with MCU main control circuit through resistance R22, the pin 4 of external connector H3 is connected on the line between resistance R19 and resistance R22;

[0021] Resistance R20 one end is connected with the VOUT end of linear voltage stabilizer U7, the other end is connected with MCU main control circuit through resistance R23, the pin 5 of external connector H3 is connected on the line between resistance R20 and resistance R23.

[0022] Relative to prior art, the utility model has the following technical effects:

[0023] The utility model discloses a MCU main control circuit, crystal oscillator, LDO power supply circuit, voltage follower circuit and PWM output circuit can be set up, and two different amplitude PWM waveforms can be exported according to demand, has 200HZ-2KHZ light modulation range, satisfies the light modulation demand of most airborne lighting system, adopts voltage follower circuit to collect voltage, high input impedance, and accurate acquisition.

[0024] The utility model is further explained below in combination with the drawings and examples. DRAWINGS

[0025] In order to more clearly explain the technical scheme in the embodiment of the utility model or prior art, the drawings needed to be used in the embodiment or prior art will be simply introduced below, and obviously, the drawings in the following description are only some embodiments of the utility model, and other drawings can be obtained according to these drawings without paying creative labor for the ordinary skilled in the art.

[0026] Figure 1 is a circuit module external interface diagram of the utility model;

[0027] Figure 2 is a circuit principle block diagram of the utility model;

[0028] Figure 3 is a circuit component connection relationship diagram of MCU master control circuit and its external configuration circuit in the utility model;

[0029] Figure 4 is a circuit component connection relationship diagram of LDO power supply circuit in the utility model;

[0030] Figure 5 is a circuit component connection relationship diagram of voltage follower circuit in the utility model;

[0031] Figure 6 is a circuit component connection relationship diagram of PWM output circuit in the utility model. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purpose, features and advantages of the utility model more apparent, obvious and easy to understand, the specific embodiments of the utility model are described in detail below in conjunction with the drawings. In the following description, a lot of specific details are set forth in order to fully understand the utility model. But the utility model can be implemented in many other ways different from the description herein, and those skilled in the art can make similar improvements without departing from the connotation of the utility model, therefore the utility model is not limited by the following disclosed specific embodiments.

[0033] In the utility model embodiment, unless explicitly defined and limited, the terms "connected", "connected" and other terms should be understood broadly, for example, can be electrically connected, can be directly connected, can be indirectly connected through intermediate medium, can be the internal communication of two elements or the interaction relationship of two elements. For ordinary skilled in the art, the specific meaning of the above-mentioned terms in the utility model embodiment can be understood according to the specific circumstances.

[0034] The embodiment provides a PWM dimming circuit, which is assembled by modules, and the module external interface is as follows Figure 1As shown: a total of 10 pins; 1 pin is a power pin, the power supply voltage is 15V. 2 pins are module GND. 3 pins are PWM output switch, low level effective. 4 pins are mode selection, pulled up by resistance for custom mode (can customize frequency, duty cycle upper limit, lower limit), pulled down by resistance for default mode, after power-on, only need to open PWM output switch and external potentiometer at 6 pins can output PWM waveform (default mode frequency 400HZ, duty cycle 10% ~ 90%). 5 pins are PWM module output pins. 6 pins are duty cycle adjustment, input 0V ~ 5V voltage through variable resistor. 7 pins are frequency setting pins, set different frequencies by connecting different resistance R to ground, range 200HZ ~ 1000HZ; the frequency calculation formula is F = 880R / (20000+R)+200. 8 pins are used to set the frequency of 7 pins by 2, pulled up effective. 9, 10 pins are used to accurately set the upper and lower limits of duty cycle, change the resistance to ground; see table 1 for details.

[0035] Table 1 duty cycle upper limit, lower limit setting

[0036] Ground resistance 0 3.6K 9.1K 16.7K 30.8K 63K 200K Duty cycle upper limit 70％ 75％ 80％ 85％ 90％ 95％ 100％ Duty cycle lower limit 0％ 5％ 10％ 15％ 20％ 25％ 30％

[0037] As Figures 2-6 shown, a PWM dimming circuit is composed of MCU master control circuit, crystal oscillator, LDO power supply circuit, voltage follower circuit and PWM output circuit.

[0038] The MCU master control circuit is used to read external configuration signals and output PWM waves with different characteristics according to the external configuration signals. The MCU master control circuit includes an MCU chip, which is selected as AT32F421K8T7. The LDO power supply circuit is used for power supply of the PWM output circuit and the MCU chip. The crystal oscillator is used to provide a basic clock signal for the MCU chip. The voltage follower circuit is mainly used to receive the duty cycle adjustment signal, convert the change of the external potentiometer rotation angle into the change of the voltage value, and output it to the MCU chip, and also has a filtering function, so that the adjustment signal received by the MCU chip is more accurate.

[0039] The MCU master control circuit is electrically connected with the crystal oscillator through the external connector H1.

[0040] The LDO power supply circuit includes an LD1 high-voltage power supply circuit and an LD2 low-voltage power supply circuit. The LD1 high-voltage power supply circuit is composed of a linear voltage stabilizer U6 (DS8640), a capacitor C2, and a capacitor C12. The LD2 low-voltage power supply circuit is composed of a linear voltage stabilizer U7 (H7233), a capacitor C13, and a capacitor C3. Specifically, a 15V external power supply is connected to the VIN terminal of the linear voltage stabilizer U6. The VIN terminal and the GND terminal of the linear voltage stabilizer U6 are connected by the capacitor C2. The GND terminal of the linear voltage stabilizer U6 is grounded. The VOUT terminal of the linear voltage stabilizer U6 is connected to the ground through the capacitor C12, and the VOUT terminal of the linear voltage stabilizer U6 outputs a 10V voltage. The VOUT terminal of the linear voltage stabilizer U6 is connected to the VIN terminal of the linear voltage stabilizer U7. The VIN terminal and the GND terminal of the linear voltage stabilizer U7 are connected by the capacitor C13. The VOUT terminal of the linear voltage stabilizer U7 is connected to the ground through the capacitor C3, and the VOUT terminal of the linear voltage stabilizer U7 outputs a 3.3V voltage.

[0041] The voltage follower circuit is composed of an operational amplifier U2 (LM321), a capacitor C5, a voltage stabilizing tube D1, a capacitor C6, resistors R1, R2, R3, R4, R18, R19, R20, R21, R22, R23, etc. Specifically, one power pin of the operational amplifier U2 is connected to the VOUT terminal of the linear voltage stabilizer U6, and the other power pin is grounded. The two power pins of the operational amplifier U2 are connected by the capacitor C5. The output terminal of the operational amplifier U2 is connected to the inverting input terminal and grounded through the resistor R1 and the voltage stabilizing tube D1. The resistor R1 and the voltage stabilizing tube D1 are connected to the MCU main control circuit (PA3 terminal of the MCU chip). The non-inverting input terminal of the operational amplifier U2 is connected to the external connector H3 through the resistors R2, R3, R4, and the capacitor C6. One end of the capacitor C6 is connected to the non-inverting input terminal of the operational amplifier U2, and the other end is grounded. The resistors R2 and R3 are connected in series between the non-inverting input terminal of the operational amplifier U2 and the external connector H3. One end of the resistor R4 is connected to the line between the resistors R2 and R3, and the other end is grounded. One end of the resistor R18 is connected to the VOUT terminal of the linear voltage stabilizer U7, and the other end is connected to the MCU main control circuit (PA6 terminal of the MCU chip) through the resistor R21. The pin 2 of the external connector H3 is connected to the line between the resistor R18 and the resistor R21. One end of the resistor R19 is connected to the VOUT terminal of the linear voltage stabilizer U7, and the other end is connected to the MCU main control circuit (PA7 terminal of the MCU chip) through the resistor R22. The pin 4 of the external connector H3 is connected to the line between the resistor R19 and the resistor R22. One end of the resistor R20 is connected to the VOUT terminal of the linear voltage stabilizer U7, and the other end is connected to the MCU main control circuit (PB0 terminal of the MCU chip) through the resistor R23. The pin 5 of the external connector H3 is connected to the line between the resistor R20 and the resistor R23.

[0042] The PWM output circuit is composed of a selection switch, pull-up resistors R15, R25, a transistor Q1 (BTA05), resistors R16, R17, etc. Specifically, a 10V voltage is electrically connected to the input end one of the selection switch through the pull-up resistor R15, a 3.3V voltage is electrically connected to the input end two of the selection switch through the pull-up resistor R25, and the output end of the selection switch is electrically connected to the collector of the transistor Q1. The base and the emitter of the transistor Q1 are connected with the resistor R17, the base of the transistor Q1 is electrically connected with one end of the resistor R16, the other end of the resistor R16 is electrically connected with the MCU main control circuit, and the collector of the transistor Q1 is connected with the external connector H2 as a PWM output port.

[0043] In summary, the power supply is input from the VIN end of the external connector H2, first passes through the linear voltage stabilizer U6 (DS8640), converts the voltage into 10V to supply the operational amplifier U2 (LM321) and the pull-up resistors R15, R25 of the collector of the transistor Q1 (BTA05). The pull-up resistors R15, R25 can be selected according to actual needs to meet different PWM amplitude requirements. The 10V voltage is converted into 3.3V by the linear voltage stabilizer U7 (H7233) to supply the MCU chip (single-chip microcomputer AT32F421K8T7) and the external configuration circuit thereof. The 3.3V power supply supplies power to the analog power supply of the single-chip microcomputer through the magnetic bead BLM15AG102SN1D (C8), and the analog ground and the digital ground are separated by the resistor R5 to ensure that the detected voltage value is more accurate. The resistors R18, R19, R20 are the basis of the pull-up resistors of the frequency setting pin and the upper and lower limit setting pin, and the external only needs to connect a resistance to ground to change the voltage to ground of the pin, and the single-chip microcomputer reads different voltages to ground to change the current PWM characteristics. The operational amplifier U2 (LM321) mainly plays a voltage following role, and the voltage output to the single-chip microcomputer is stabilized through the filtering of the capacitor C6. The front-stage resistors R2, R4 convert the 0V-5V voltage signal into 0V-3V.

[0044] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present application, or modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present application, by using the disclosed methods and technical contents. Therefore, any equivalent changes made according to the shape, structure and principle of the present application, which do not depart from the content of the technical solution of the present application, should be covered by the protection scope of the present application.

Claims

1. A PWM dimming circuit, characterized in that: Including MCU main control circuit, LDO power supply circuit, voltage follower circuit and PWM output circuit; The LDO power supply circuit is electrically connected to the MCU main control circuit and the PWM output circuit; The LDO power supply circuit is electrically connected to the voltage follower circuit, and the voltage follower circuit is electrically connected to the MCU main control circuit; The MCU main control circuit is electrically connected to the PWM output circuit; The LDO power supply circuit includes an LD1 high voltage power supply circuit and an LD2 low voltage power supply circuit connected to each other; The PWM output circuit includes a selection switch, a pull-up resistor R15, a pull-up resistor R25 and a transistor Q1. The output end of the LD1 high-voltage power supply circuit is electrically connected to the input end 1 of the selection switch through the pull-up resistor R15. The output end of the LD2 low-voltage power supply circuit is electrically connected to the input end 2 of the selection switch through the pull-up resistor R25. The output end of the selection switch is electrically connected to the collector of the transistor Q1.

2. A PWM dimming circuit according to claim 1, characterized in that: The PWM output circuit also includes resistors R16 and R17. Resistor R17 is connected between the base and emitter of transistor Q1. The base of transistor Q1 is electrically connected to one end of resistor R16, and the other end of resistor R16 is electrically connected to the MCU main control circuit. The collector of transistor Q1 serves as a PWM output port and is connected to the external connector H2.

3. A PWM dimming circuit according to claim 1, characterized in that: It also includes a crystal oscillator, and the MCU main control circuit is electrically connected to the crystal oscillator through an external connector H1.

4. The PWM dimming circuit according to claim 1, wherein: The LDO power supply circuit includes a linear regulator U6 and a linear regulator U7. An external power supply is connected to the VIN terminal of the linear regulator U6. A capacitor C2 is connected between the VIN terminal and the GND terminal of the linear regulator U6. The GND terminal of the linear regulator U6 is grounded. The VOUT terminal of the linear regulator U6 is grounded through a capacitor C12. The VOUT terminal of the linear regulator U6 is connected to the VIN terminal of the linear regulator U7. A capacitor C13 is connected between the VIN terminal and the GND terminal of the linear regulator U7. The VOUT terminal of the linear regulator U7 is grounded through a capacitor C3.

5. A PWM dimming circuit as claimed in claim 4, characterized in that: The voltage follower circuit includes an operational amplifier U2, one power pin of the operational amplifier U2 is connected to the VOUT terminal of the linear regulator U6, and the other power pin is grounded; a capacitor C5 is connected between the two power pins of the operational amplifier U2, the output terminal of the operational amplifier U2 is connected to the inverting input terminal and is grounded through a resistor R1 and a voltage regulator D1, and the line between the resistor R1 and the voltage regulator D1 is connected to the MCU main control circuit.

6. A PWM dimming circuit as claimed in claim 5, characterized in that: The non-inverting input terminal of the operational amplifier U2 is connected to the external connector H3 through resistors R2, R3, R4 and capacitor C6; one end of capacitor C6 is connected to the non-inverting input terminal of the operational amplifier U2, and the other end is grounded; resistors R2 and R3 are connected in series between the non-inverting input terminal of the operational amplifier U2 and the external connector H3; one end of resistor R4 is connected to the line between resistors R2 and R3, and the other end is grounded.

7. A PWM dimming circuit as claimed in claim 6, characterized in that: The voltage follower circuit further includes resistors R18, R19, R20, R21, R22, and R23; One end of resistor R18 is connected to the VOUT terminal of linear regulator U7, and the other end is connected to the MCU main control circuit through resistor R21. Pin 2 of external connector H3 is connected to the line between resistor R18 and resistor R21. One end of resistor R19 is connected to the VOUT terminal of linear regulator U7, and the other end is connected to the MCU main control circuit through resistor R22. Pin 4 of external connector H3 is connected to the line between resistor R19 and resistor R22. One end of the resistor R20 is connected to the VOUT terminal of the linear regulator U7, and the other end is connected to the MCU main control circuit through the resistor R23. Pin 5 of the external connector H3 is connected to the line between the resistor R20 and the resistor R23.

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