A constant current source circuit supporting PWM modulation

Abstract

The present invention discloses a constant current source circuit supporting PWM modulation, which includes an amplitude adjustment unit, a voltage extraction unit and a constant current output unit; the amplitude adjustment unit is used to receive a PWM input signal, adjust the input signal into a voltage signal with a specified amplitude and frequency, and output it to the voltage extraction unit; the voltage extraction unit is used to convert the received voltage signal into a DC voltage signal whose voltage is proportional to the duty cycle, and output it to the constant current output unit; the constant current output unit is used to convert the received DC voltage signal into a constant DC current signal and output it. The present invention integrates the constant current source with PWM regulation, realizes the adjustment of the output current magnitude by adjusting the PWM duty cycle, reduces the cost of the constant current source and the circuit complexity, and is particularly suitable for some occasions with low-cost requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, in particular to a constant current source circuit supporting PWM modulation. Background Art

[0002] PWM stands for pulse width modulation. Pulse width modulation is a very effective technology that uses the digital output of a microprocessor to control analog circuits. It is widely used in many fields, from measurement and communication to power control and conversion. Constant current sources are used in many current circuit systems, but few existing constant current source technologies integrate constant current sources with PWM control. Even if they are integrated, the cost is relatively high. Currently, the design of constant current source circuits that can be PWM modulated generally uses dedicated power supply chips or digital circuits. This is ideal for high-end applications, but for some low-cost applications and applications that only require constant current generation, digital control chips require additional power supplies and complex isolation methods. The circuit is complex and the cost is relatively high, which cannot meet low-cost requirements. Summary of the Invention

[0003] The purpose of the present invention is to provide a constant current source circuit supporting PWM modulation, integrating the constant current source with PWM regulation, and reducing the cost and circuit complexity of the constant current source.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: a constant current source circuit supporting PWM modulation, comprising an amplitude adjustment unit, a voltage extraction unit and a constant current output unit;

[0005] The amplitude adjustment unit is used to receive the PWM input signal, adjust the input signal to a voltage signal of specified amplitude and frequency, and output it to the voltage extraction unit;

[0006] The voltage extraction unit is used to convert the received voltage signal into a DC voltage signal whose voltage is proportional to the duty cycle, and output it to the constant current output unit;

[0007] The constant current output unit is used to convert the received DC voltage signal into a constant DC current signal and output it.

[0008] Optionally, the amplitude adjustment unit includes a multi-channel analog switch chip, the control input end of the multi-channel analog switch chip is connected to the PWM input signal, and the output end is connected to the pull-up resistor to adjust the input PWM signal to a voltage signal of a specified amplitude and output it.

[0009] Optionally, the output end of the multi-channel analog switch chip is further connected to a resistance-capacitance filter circuit.

[0010] Optionally, the multi-channel analog switch chip uses an analog switch chip with the model number ADG433. Among its four input terminal pins, at least any one of IN1 and IN4, and any one of IN2 and IN3 are connected to the PWM input signal; the output terminal S pins are all grounded through pull-down resistors, the output terminal D pins are all connected to a resistor-capacitor filtering circuit, and the D pins are connected to the filtering resistor in the resistor-capacitor filtering circuit after connecting a pull-up resistor, and a reference voltage source is connected between the pull-up resistor and the filtering resistor.

[0011] ADG433 is a single-chip CMOS device with four independent and selectable switches. The on-condition of two switches is that the control input is at a logic high level, and the control logic of the other two switches is opposite. In the present invention, any pair of input-output switch channels with opposite control input logics can be selected to achieve: when the input PWM waveform is at a low level or a high level, one switch is conducting and outputting a pulse voltage signal with a specified amplitude at any time. The frequency of the voltage signal is the same as that of the PWM input signal, and the amplitude is determined by the resistor-capacitor filtering, the pull-up resistor, and the reference voltage source, and can be adjusted as needed. ADG433 can also be replaced with other analog switch chips, such as ADG432 and ADG431. The control logics of each channel in these two chips are the same, and the conversion from the PWM signal to a continuous pulse voltage signal can be achieved by adding a NOT gate.

[0012] Optionally, the voltage extraction unit includes a voltage follower, a low-pass filter, and a voltage division circuit arranged in sequence; the voltage follower receives the voltage signal output by the amplitude adjustment unit, adjusts the input and output impedance of the signal, and then outputs it to the low-pass filter for high-frequency signal filtering. The output terminal of the low-pass filter is connected to the voltage division circuit to output a DC voltage signal with a specified voltage and the voltage being proportional to the duty cycle.

[0013] Optionally, the voltage extraction unit includes a TL082 dual operational amplifier. The positive input terminal of its first operational amplifier is connected to the voltage signal output by the amplitude adjustment unit, and the negative input terminal is connected to the first output terminal to serve as a voltage follower; the positive input terminal of the second operational amplifier is connected to the first output terminal, the negative input terminal is connected to the second output terminal, and the second output terminal outputs the DC voltage signal; a second-order low-pass filter circuit is arranged between the first output terminal and the positive input terminal of the second operational amplifier;

[0014] The second-order low-pass filter circuit includes a resistor R1 and a resistor R2 connected in series between the first output terminal and the positive input terminal of the second operational amplifier, a capacitor C1 with one end connected to the connection point between R2 and the positive input terminal of the second operational amplifier and the other end grounded, and a capacitor C2 with one end connected to the connection point between R1 and R2 and the other end connected to the negative input terminal of the second operational amplifier; the second-order low-pass filter circuit and the second operational amplifier form the low-pass filter.

[0015] Optionally, the voltage dividing circuit includes resistors R3 and R4 connected in series. The connection point of R3 and R4 is the DC voltage signal output terminal. The other end of resistor R4 is grounded, and a capacitor C3 is connected in parallel thereto.

[0016] The voltage of the DC voltage signal satisfies the following relationship:

[0017] V FY_OUT = V LPF_OUT *R4 / (R3 + R4) = V LPF_OUT / 2

[0018] In the formula, V LPF_OUT is the voltage input to the inverting input terminal of the second operational amplifier.

[0019] Optionally, the constant current output unit includes a voltage follower, a push-pull output circuit, and a subtractor. The voltage follower receives the DC voltage signal output by the voltage extraction unit, adjusts the input and output impedance of the signal, and then transmits it to the subtractor through the push-pull output circuit, converting it into a constant DC current signal and outputting it.

[0020] Optionally, the voltage follower uses a TL082 dual operational amplifier. The non-inverting input terminal of its first operational amplifier is connected to the output terminal of the voltage extraction unit, and the inverting input terminal is connected to the first output terminal through a capacitor C11 and to the second output terminal through a resistor R31.

[0021] The output terminal of the push-pull output circuit is connected in series with resistors R10 and RL. The opposite end of the connection between resistor RL and one end of resistor R10 is the DC output terminal of the constant current output unit. A resistor R11 and a resistor R13 are connected in series between the connection point of the output terminal of the push-pull output circuit and resistor R10 and the ground terminal. The connection point of resistor R11 and resistor R13 is connected to the non-inverting input terminal of the second operational amplifier of the voltage follower. The connection point of resistor R10 and resistor RL is connected to the inverting input terminal of the second operational amplifier of the voltage follower through a resistor R12. The inverting input terminal of the second operational amplifier is connected to the second output terminal through a resistor R14. Among them, resistors R11, R12, R13, and R14 form the subtractor.

[0022] Optionally, in the constant current output unit, R11 = R12, R13 = R14, and the input-output relationship satisfies:

[0023] V O = (R13 / R11)(V1 - V2)

[0024] I O = (V1 - V2) / R10

[0025] V O is the voltage of the second output terminal of the voltage follower, V1 is the voltage output by the push-pull output circuit, V2 is the voltage at the connection point of resistor R10 and resistor RL, and I OThe current output at the DC output terminal.

[0026] Advantageous effects

[0027] The constant current source circuit of the present invention is composed of common analog devices such as analog switches, operational amplifiers, and triodes to form a constant current source circuit. It can adjust the output current by adjusting the PWM duty cycle, and has the advantages of simple circuit structure, convenient control, and high output accuracy. It is especially suitable for some occasions with low-cost requirements. Description of the drawings

[0028] Figure 1 The figure shows a schematic diagram of the functional module composition of the constant current source circuit of the present invention;

[0029] Figure 2 The figure shows a circuit schematic diagram of the amplitude adjustment unit in an embodiment of the present invention;

[0030] Figure 3 The figure shows Figure 1 A schematic diagram of the PWM input / output signal waveforms of the amplitude adjustment unit;

[0031] Figure 4 The figure shows a circuit schematic diagram of the voltage extraction unit in an embodiment of the present invention;

[0032] Figure 5 The figure shows a circuit schematic diagram of the constant current output unit in an embodiment of the present invention. Detailed implementation manners

[0033] The following is further described in conjunction with the drawings and specific embodiments.

[0034] Embodiment 1

[0035] This embodiment introduces a constant current source circuit supporting PWM modulation. Refer to Figure 1 , which includes an amplitude adjustment unit, a voltage extraction unit, and a constant current output unit;

[0036] The amplitude adjustment unit is used to receive the PWM input signal PWM1, and adjust the input signal to a pulse voltage signal PWM2 with a specified amplitude and frequency, that is, Figure 2 PWM_OUT in

[0037] and output it to the voltage extraction unit; FY_OUT The voltage extraction unit is used to convert the received voltage signal into a DC voltage signal V

[0038] whose voltage is proportional to the duty cycle, and output it to the constant current output unit;

[0039] In this embodiment, the amplitude adjustment circuit adjusts an input signal of 6 kHz and 0 - 3.3 V into a signal of 6 kHz and -10 V to +10 V. The voltage extraction circuit performs low-pass filtering on the -10 V to +10 V signal to obtain a DC voltage signal proportional to the duty cycle. The constant current output circuit converts the DC voltage signal into a constant DC current signal.

[0040] As Figure 2 shown, the amplitude adjustment unit includes a multiplex analog switch chip. Its control input terminal is connected to the PWM input signal, and the output terminal is connected to pull-up resistors R23 - R26. The pull-up resistors are connected to the reference power supply to adjust the input PWM signal into a voltage signal with a specified amplitude and output it. The output terminal of the multiplex analog switch chip is connected to a resistor-capacitor filtering circuit.

[0041] In this embodiment, the multiplex analog switch chip uses an analog switch chip with the model number ADG433. Among its four input terminal pins, IN1 - IN4 are respectively connected to the PWM input signal with a waveform frequency of 6 kHz and an amplitude of 0 - 3.3 V. The output terminal S pins are all grounded through pull-down resistors R29 or R30. The output terminal D pins are all connected to the resistor-capacitor filtering circuit, and the D pins are connected to the filtering resistor in the resistor-capacitor filtering circuit after connecting the pull-up resistor. A ±10 V reference voltage source is connected between the pull-up resistor and the filtering resistor.

[0042] ADG433 is a single-chip CMOS device with four independent and selectable switches. The on conditions of two switches are that the control input is at a logic high level, and the control logics of the other two switches are opposite. When the PWM waveforms input at the four input ports are at a low level or a high level, two switches conduct and output a pulse voltage signal with a specified amplitude at any time. Therefore, in this embodiment, only any pair of two channels with opposite control logics among D1 - S1 to D4 - S4 needs to be selected to output the PWM_OUT signal. For example, D1 - S1 and D2 - S2 are selected. When the input PWM signal is 0 V, D1 and S1 of the analog switch are disconnected, and D2 and S2 are connected, and the output signal PWM_OUT is 10 V. When the input PWM signal is 3.3 V, D1 and S1 of the analog switch are connected, and D2 and S2 are disconnected, and the output signal PWM_OUT is -10 V. It can be seen that the waveforms of the input PWM signal and the output PWM_OUT signal are as Figure 3 shown. The frequency of the output PWM voltage signal is the same as that of the PWM input signal, and the amplitude is determined by the resistor-capacitor filtering, the pull-up resistor, and the reference voltage source, and can be adjusted as needed.

[0043] Above, ADG433 can also be replaced with other analog switch chips, such as ADG4, whose control logics of each channel are the same, and the conversion from the PWM signal to a continuous pulse voltage signal can be achieved by adding a NOT gate.

[0044] As shown Figure 4 in the figure, the voltage extraction unit includes a voltage follower, a VCVS (voltage-controlled voltage source) low-pass filter, and a voltage division circuit arranged in sequence. The voltage follower receives the voltage signal output by the amplitude adjustment unit, adjusts the input and output impedance of the signal, and then outputs it to the low-pass filter for high-frequency signal filtering. The output end of the low-pass filter is connected to the voltage division circuit to output a DC voltage signal with a specified voltage and the voltage being proportional to the duty cycle.

[0045] In this embodiment, the voltage extraction unit uses a TL082 dual operational amplifier. On the one hand, it is used as a voltage follower to adjust the input and output impedance of the signal. On the other hand, it is used as a VCVS low-pass filter, and a second-order low-pass filter is composed of R1, R2, C1, and C2. The non-inverting input terminal pin 3 of the first operational amplifier of TL082 accesses the voltage signal output by the amplitude adjustment unit, and the inverting input terminal pin 2 is connected to the first output terminal pin 1 to serve as a voltage follower. The non-inverting input terminal pin 5 of the second operational amplifier is connected to the first output terminal pin 1, the inverting input terminal pin 6 is connected to the second output terminal pin 7, and the second output terminal outputs the DC voltage signal V LPF_OUT after passing through the resistor R3. A second-order low-pass filter circuit is provided between the first output terminal and the non-inverting input terminal of the second operational amplifier.

[0046] In the second-order low-pass filter circuit, the resistors R1 and R2 are connected in series between the first output terminal and the non-inverting input terminal of the second operational amplifier. One end of the capacitor C1 is connected to the connection point between R2 and the non-inverting input terminal of the second operational amplifier, and the other end is grounded. One end of the capacitor C2 is connected to the connection point between R1 and R2, and the other end is connected to the pin 7 of the TL082 dual operational amplifier. The second-order low-pass filter circuit and the second operational amplifier of the TL082 dual operational amplifier form the low-pass filter.

[0047] When R1 = R2 = 20 kΩ and C1 = C2 = 1 nF, the low-pass cut-off frequency can be calculated as fc = 800 Hz.

[0048] When the low-pass filter inputs a PWM signal of 6 kHz, 0 - 3.3 V, the 6 kHz high-frequency signal is completely filtered out, and only the DC voltage signal proportional to the duty cycle is output. By changing the duty cycle (0 - 100%), the magnitude of the DC voltage is adjusted. The higher the duty cycle, the larger the DC voltage.

[0049] The voltage division circuit includes the resistors R3 and R4 connected in series. The connection point of R3 and R4 is the output terminal of the DC voltage signal. The other end of the resistor R4 is grounded, and a capacitor C3 is connected in parallel thereto. The magnitude of the output voltage after voltage division is determined by the resistance values of R3 and R4. When R3 = R4 = 30 kΩ, the voltage of the DC voltage signal satisfies the following relationship:

[0050] V FY_OUT = V LPF_OUT*R4 / (R3+R4) = V LPF_OUT / 2

[0051] wherein, V LPF_OUT is the voltage input to the inverting input terminal of the second operational amplifier.

[0052] As Figure 5 shown, the constant current output unit includes a voltage follower, a push-pull output circuit, and a subtractor. The voltage follower receives the DC voltage signal V output by the voltage extraction unit FY_OUT , adjusts the input and output impedance of the signal, and then transmits it to the subtractor through the push-pull output circuit, converting it into a constant DC current signal Io and outputting it.

[0053] The subtractor is composed of resistors R11 to R14. The voltage follower uses a TL082 dual operational amplifier. The non-inverting input terminal of its first operational amplifier is connected to the output terminal of the voltage extraction unit, and the inverting input terminal is connected to the first output terminal through a capacitor C11 and to the second output terminal through a resistor R31;

[0054] The output terminal of the push-pull output circuit is connected in series with a resistor R10 and RL. The opposite end of RL connected to one end of the resistor R10 is the DC output terminal of the constant current output unit; A resistor R11 and a resistor R13 are connected in series between the connection point of the output terminal of the push-pull output circuit and the resistor R10 and the ground terminal. The connection point of the resistor R11 and the resistor R13 is connected to the non-inverting input terminal of the second operational amplifier of the voltage follower; The connection point of the resistor R10 and RL is connected to the inverting input terminal of the second operational amplifier of the voltage follower through a resistor R12, and the inverting input terminal of the second operational amplifier is connected to the second output terminal through a resistor R14.

[0055] In the constant current output unit, the input-output relationship satisfies: VP = V1 * R13 / (R11 + R13)

[0056] (V2 - VP) / R12 = (VP - VO) / R14

[0057] When R11 = R12 and R13 = R14, then V O = (R13 / R11)(V1 - V2)

[0058] When R11 = 200 kΩ and R13 = 470 kΩ, Vo = 2.35(V1 - V2)

[0059] It can be seen that the subtractor mainly realizes the function of amplifying the difference between the voltages V1 and V2 by 2.35 times.

[0060] When the input PWM duty cycle is 100%, V FY_OUT = 4.58 V, V O = V FY_OUT = 4.58 V, V1 - V2 = Vo / 2.35 = 1.95 V.

[0061] When R10 = 39 Ω, Io = (V1 - V2) / R10 = 1.95 V / 39 Ω = 50 mA.

[0062] When the input PWM duty cycle is 0%, V O = V FY_OUT = -4.58 V, V1 - V2 = Vo / 2.35 = -1.95 V.

[0063] When R10 = 39 Ω, Io = (V1 - V2) / R10 = -1.95 V / 39 Ω = -50 mA.

[0064] It can be seen that the constant current source circuit supporting PWM modulation in this embodiment can adjust the magnitude of the output current by adjusting the PWM duty cycle, and the current output range is -50 mA to 50 mA. When the input PWM duty cycle is 0%, the output current is -50 mA; when the input PWM duty cycle is 100%, the output current is 50 mA. R11 to R14 use 0.1% high-precision resistors, and the output current accuracy of the circuit can reach ±0.7 mA. It has the advantages of simple structure, convenient control, high-precision output, etc., and is especially suitable for some occasions with low-cost requirements.

[0065] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose and scope protected by the claims of the present invention. These all fall within the protection scope of the present invention.

Claims

1. A constant current source circuit supporting PWM modulation, characterized in that, It includes an amplitude adjustment unit, a voltage extraction unit, and a constant current output unit; The amplitude adjustment unit is used to receive a PWM input signal, adjust the input signal into a voltage signal with a specified amplitude and frequency, and output it to the voltage extraction unit; The voltage extraction unit is used to convert the received voltage signal into a DC voltage signal whose voltage is proportional to the duty cycle, and output it to the constant current output unit; The constant current output unit is used to convert the received DC voltage signal into a constant DC current signal and output it; The constant current output unit includes a voltage follower, a push-pull output circuit, and a subtractor. The voltage follower receives the DC voltage signal output by the voltage extraction unit, adjusts the input and output impedance of the signal, and then transmits it to the subtractor through the push-pull output circuit, converts it into a constant DC current signal, and outputs it; The voltage follower uses a TL082 dual operational amplifier. The non-inverting input terminal of its first operational amplifier is connected to the output terminal of the voltage extraction unit, and the inverting input terminal is connected to the first output terminal through a capacitor C11 and to the second output terminal through a resistor R31; The output terminal of the push-pull output circuit is connected in series with a resistor R10 and an RL. The opposite end of the RL connected to one end of the resistor R10 is the DC output terminal of the constant current output unit; A resistor R11 and an R13 are connected in series between the connection point of the push-pull output circuit output terminal and the resistor R10 and the ground terminal, and the connection point of the resistor R11 and the R13 is connected to the non-inverting input terminal of the second operational amplifier of the voltage follower; The connection point of the resistor R10 and the RL is connected to the inverting input terminal of the second operational amplifier of the voltage follower through a resistor R12, and the inverting input terminal of the second operational amplifier is connected to the second output terminal through a resistor R14; Among them, the resistors R11, R12, R13, and R14 form the subtractor.

2. The constant current source circuit supporting PWM modulation according to claim 1, characterized in that, The amplitude adjustment unit includes a multiplexed analog switch chip. The control input terminal of the multiplexed analog switch chip accesses the PWM input signal, and the output terminal is connected to a pull-up resistor to adjust the input PWM signal into a voltage signal with a specified amplitude and output it.

3. The constant current source circuit supporting PWM modulation according to claim 2, wherein The output terminal of the multiplexed analog switch chip is also connected with a resistor-capacitor filter circuit.

4. The constant current source circuit supporting PWM modulation according to claim 2 or 3, characterized in that, The multiplexed analog switch chip uses an analog switch chip with the model of ADG433. Among its four input terminal pins, at least any one of IN1 and IN4, and any one of IN2 and IN3 are connected to the PWM input signal; The S pins of the output terminals are grounded through pull-down resistors, the D pins of the output terminals are connected to the resistor-capacitor filter circuit, and the D pins are connected to the filter resistor in the resistor-capacitor filter circuit after connecting the pull-up resistor, and a reference voltage source is connected between the pull-up resistor and the filter resistor.

5. The constant current source circuit supporting PWM modulation according to claim 1, characterized in that, The voltage extraction unit includes a voltage follower, a low-pass filter, and a voltage division circuit arranged in sequence; The voltage follower receives the voltage signal output by the amplitude adjustment unit, adjusts the input and output impedance of the signal, and then outputs it to the low-pass filter for high-frequency signal filtering processing. The output terminal of the low-pass filter is connected to the voltage division circuit to output a DC voltage signal with a specified voltage and whose voltage is proportional to the duty cycle.

6. The constant current source circuit supporting PWM modulation according to claim 5, characterized in that, The voltage extraction unit includes a TL082 dual operational amplifier. The non-inverting input terminal of its first operational amplifier is connected to the voltage signal output by the amplitude adjustment unit, and the inverting input terminal is connected to the first output terminal to serve as a voltage follower. The non-inverting input terminal of the second operational amplifier is connected to the first output terminal, and the inverting input terminal is connected to the second output terminal. The second output terminal outputs the DC voltage signal. A second-order low-pass filter circuit is provided between the first output terminal and the non-inverting input terminal of the second operational amplifier. The second-order low-pass filter circuit includes resistors R1 and R2 connected in series between the first output terminal and the non-inverting input terminal of the second operational amplifier, a capacitor C1 with one end connected to the connection point between R2 and the non-inverting input terminal of the second operational amplifier and the other end grounded, and a capacitor C2 with one end connected to the connection point between R1 and R2 and the other end connected to the inverting input terminal of the second operational amplifier. The second-order low-pass filter circuit and the second operational amplifier form the low-pass filter.

7. The constant current source circuit supporting PWM modulation according to claim 6, characterized in that, The voltage dividing circuit includes resistors R3 and R4 connected in series. The connection point of R3 and R4 is the output terminal of the DC voltage signal. The other end of resistor R4 is grounded, and a capacitor C3 is connected in parallel thereto. The voltage of the DC voltage signal satisfies the following relational expression: ， wherein, is the voltage input to the inverting input terminal of the second operational amplifier.

8. The constant current source circuit supporting PWM modulation according to claim 1, characterized in that, In the constant current output unit, R11 = R12, R13 = R14, and the input-output relationship satisfies: ， ， is the voltage at the second output terminal of the voltage follower, is the voltage output by the push-pull output circuit, is the voltage at the connection point of resistor R10 and RL, is the current output by the DC output terminal.

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