CN111141949A - Alternating voltage sampling circuit for output power control and design method thereof - Google Patents

Alternating voltage sampling circuit for output power control and design method thereof Download PDF

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CN111141949A
CN111141949A CN202010088867.2A CN202010088867A CN111141949A CN 111141949 A CN111141949 A CN 111141949A CN 202010088867 A CN202010088867 A CN 202010088867A CN 111141949 A CN111141949 A CN 111141949A
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resistor
voltage
operational amplifier
circuit
amplifier chip
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CN111141949B (en
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王念春
崔熠凡
彭斌
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Southeast University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/04—Voltage dividers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
    • G01R15/22—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-emitting devices, e.g. LED, optocouplers

Abstract

The invention discloses an alternating voltage sampling circuit for output power control and a design method thereof, wherein the alternating voltage sampling circuit comprises an alternating voltage dividing circuit, a second-order band-pass active filter circuit, a high-precision full-wave rectifier circuit, a comparator circuit and an isolation sampling circuit, wherein alternating input voltage is input into the alternating voltage dividing circuit, the output end of the alternating voltage dividing circuit is connected with the input end of the second-order band-pass active filter circuit, the output end of the second-order band-pass active filter circuit is connected with the input end of the high-precision full-wave rectifier circuit, the output end of the high-precision full-wave rectifier circuit is connected with the input end of the comparator circuit, and the. The method avoids the increase of sampling delay and cost of the switching power supply caused by the fact that the sampling of the primary-side single chip microcomputer is transmitted to the secondary side, and enables the vehicle-mounted power supply to accurately reduce power according to the input voltage.

Description

Alternating voltage sampling circuit for output power control and design method thereof
Technical Field
The invention belongs to the technical field of electronics, and mainly comprises an alternating current voltage division circuit, a second-order band-pass active filter circuit, a high-precision full-wave rectifier circuit, a comparator circuit and an isolation sampling circuit; to an ac voltage sampling circuit for output power control and a method of designing the same.
Background
The switch power supply is a power supply which utilizes the modern power electronic technology to control the time proportion of the on and off of a switch tube and maintain the stability of output voltage. The switching power supply is generally composed of a Pulse Width Modulation (PWM) control chip (IC), a transformer, and a switching tube (MOSFET). With the development and innovation of power electronic technology, the technology of the switching power supply is continuously innovated. At present, the switching power supply is widely applied to almost all electronic devices due to its characteristics of small size, light weight and high efficiency, and is an indispensable power supply mode for the rapid development of the electronic information industry.
In order to meet the requirements of equipment, the switching power supply requires wide ranges of input voltage and output voltage, and when the difference between the input voltage and the output voltage is large, a transformer can be used, so that the isolation effect is achieved, and the wide output voltage range can be adapted. In the field of new energy, a vehicle-mounted power supply needs to adapt to the voltage fluctuation of a power grid, for example, the European voltage is 110V, the domestic commercial power (alternating current input voltage) is 220V, and the commercial power refers to single-phase alternating current; in order to meet the charging requirement, when the input voltage is reduced to a certain value, the vehicle-mounted power supply cannot be shut down and only can be operated in a power reducing mode.
In the charging device of the electric vehicle, the input voltage sampling circuit of the switching power supply aims to realize power reduction and shutdown according to a certain rule according to the currently sampled alternating input voltage value and prevent the possible overheating damage caused by overlarge current of a power switch tube (MOSFET) under the condition of low input voltage. The sampling of the input voltage of the low-power switch power supply mostly directly adopts the undervoltage protection function of a control chip (IC), the input voltage enters the inverting input end of the internal operational amplifier of the IC through resistance voltage division and is compared with the reference voltage of the non-inverting input end, when the input voltage is smaller than the reference voltage, the PWM driving signal is closed, namely, when the input voltage is lower than a certain value, the switch power supply is directly shut down. The input voltage range under the mode is narrow, and certain requirements are required on the input voltage during operation.
In order to realize power reduction, real-time input voltage needs to be sampled at the primary side of the vehicle-mounted power supply, and because a chip for realizing the power reduction control function is arranged at the secondary side, the chip needs to collect output voltage, output current and the like and control the output voltage and the output current according to the magnitude of the input voltage. At present, the charging machine industry mostly adopts a method of using a single chip microcomputer on a primary side to sample input voltage. As shown in fig. 1, the input voltage is rectified and filtered to obtain a direct current component, and the direct current component enters a sampling circuit after passing through a voltage division circuit; the singlechip converts the input voltage according to the proportional voltage of the ADC port, the communication between the two chips needs to pass through the optical coupler because the two chips are in an isolated state, the singlechip transmits the value of the sampled input voltage into the control chip on the secondary side through serial communication and the optical coupler, and the control chip controls the driving signal of the main circuit according to the obtained voltage and controls the output power. The method has the defects of time delay and inaccuracy in the process of filtering after sampling and transmitting to the control chip through the serial port, and the problem that a single chip microcomputer is added on the primary side, so that the cost is increased, the circuit is complex, the hardware cost is increased, and the workload of research and development personnel is increased in the aspect of software.
Disclosure of Invention
The purpose of the invention is as follows: in order to solve the technical defects of time delay and inaccuracy of input voltage sampling in the prior art, the alternating voltage sampling circuit for output power control and the design method thereof are provided, so that the problems of time delay and cost increase of the switching power supply caused by the fact that a primary-side single chip microcomputer samples and then transmits the samples to a secondary side are avoided, and the vehicle-mounted power supply accurately performs power reduction according to the input voltage.
The technical scheme is as follows: in order to realize the purpose, the invention adopts the following technical scheme:
the utility model provides an alternating voltage sampling circuit for output power control, including exchanging bleeder circuit, second order band-pass active filter circuit, high accuracy full wave rectifier circuit, comparator circuit and isolation sampling circuit, wherein exchange input voltage input exchange bleeder circuit, exchange bleeder circuit output and second order band-pass active filter circuit input and be connected, second order band-pass active filter circuit output and high accuracy full wave rectifier circuit input are connected, high accuracy full wave rectifier output is connected with comparator circuit input, comparator circuit output and isolation sampling circuit input are connected.
Optionally, the ac voltage dividing circuit includes a resistor R4 and a resistor R6, the ac input voltage is connected to the resistor R4 and then connected to the ground GND through a resistor R6, and the center points of the resistor R4 and the resistor R6 are connected to the input end of the second-order band-pass active filter circuit; the voltage of the divided alternating current input voltage can be changed by changing the resistance values of the resistor R and the resistor R6.
Optionally, the second-order band-pass active filter circuit includes a resistor R3, a resistor R5, a resistor R9, a capacitor C1, a capacitor C3, a capacitor C4, and an operational amplifier chip OA 1; the output voltage of the alternating current voltage division circuit is connected to a resistor R5 and then connected to the negative input end of an operational amplifier chip OA1 through a capacitor C3; one end of the resistor R9 is connected to the center point of the resistor R5 and the capacitor C3, and the other end is connected to the ground GND; the output end of the operational amplifier chip OA1 is connected to the central points of the resistor R5 and the capacitor C3 and the negative input end of the operational amplifier chip OA1 through a capacitor C1 and a resistor R3 respectively; the positive power supply VCC is connected to the positive input end of the operational amplifier chip OA1 after being divided by the resistor R12 and the resistor R15, and is connected to the ground GND through the capacitor C4; the positive and negative power supply terminals of the operational amplifier chip OA1 are connected to the positive voltage VCC and the ground GND, respectively.
Optionally, the high-precision full-wave rectifier circuit comprises a resistor R1, a resistor R2, a resistor R7, a diode D1, a diode D2, a capacitor C2, and operational amplifier chips OA2 and OA 3; the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA2, the cathode input end of the second-order band-pass active filter circuit is connected in parallel with a capacitor C2 through a diode D1, a resistor R1 is connected to the output end and the cathode input end of the operational amplifier chip OA3, and the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA3 through a diode D2; the negative input end of the operational amplifier chip OA3 is connected to the output end of the operational amplifier chip OA3 through a resistor R2, and the positive input end of the operational amplifier chip OA3 is connected to a ground wire R7 through a resistor R7; the positive and negative power supply ends of the operational amplifier chips OA2 and OA3 are respectively connected to the positive voltage VCC and the ground GND; the high-precision full-wave rectifier circuit converts sinusoidal alternating current into direct current.
Optionally, the comparator circuit includes a voltage stabilizing chip, an operational amplifier chip OA4, a resistor R11, a resistor R13 and a resistor R16, the voltage stabilizing chip, the resistor R11, the resistor R13 and the resistor R16 are configured to generate a precise and stable dc voltage, and the dc voltage is connected to the negative voltage input terminal of the operational amplifier chip OA 4; the output end of the high-precision full-wave rectifier circuit is connected to the positive voltage input end of the operational amplifier chip OA 4; the positive and negative input voltages of the operational amplifier chip OA4 are compared by the operational amplifier chip, and then a square wave signal with the amplitude VCC is generated at the output end of the operational amplifier chip.
Optionally, the isolation circuit part in the isolation sampling circuit includes an isolation optocoupler, a resistor R10, a resistor R14, a resistor R8, the output end of the comparator circuit is connected with the first port of the isolation optocoupler through a resistor R10, the second port of the isolation optocoupler is connected with GND through a resistor R14, the third port of the isolation optocoupler is connected with the power supply through a resistor R8, and the fourth port of the isolation optocoupler is connected with the SGND.
The invention also provides a design method of the alternating voltage sampling circuit for controlling the output power, which comprises the following design steps:
(1) establishing an alternating current voltage dividing circuit which comprises a resistor R4 and a resistor R6, wherein alternating current input voltage is connected to a resistor R4 and then connected to a ground wire GND through a resistor R6, and the voltage of the alternating current input voltage after voltage division can be changed by changing the resistance values of the resistor R4 and the resistor R6; setting the voltage obtained by the AC voltage divider circuit to V1Voltage V obtained by an AC voltage divider circuit1And an alternating current input voltage VinThe relationship of (1) is:
Figure BDA0002383027230000031
(2) establishing a second-order band-pass active filter circuit which comprises a resistor R3, a resistor R5, a resistor R9, a capacitor C1, a capacitor C3, a capacitor C4 and an operational amplifier chip OA 1; the output voltage of the alternating current voltage division circuit is connected to a resistor R5 and then connected to the negative input end of an operational amplifier chip OA1 through a capacitor C3; one end of the resistor R9 is connected to the center point of the resistor R5 and the capacitor C3, and the other end is connected to the ground GND; the output end of the operational amplifier chip OA1 is connected to the central points of the resistor R5 and the capacitor C3 and the negative input end of the operational amplifier chip OA1 through a capacitor C1 and a resistor R3 respectively; the positive power supply VCC is connected to the positive input end of the operational amplifier chip OA1 after being divided by resistors R12 and R15, and is connected to the ground GND through a capacitor C4; the positive and negative power supply terminals of the operational amplifier chip OA1 are respectivelyTo a positive voltage VCC and ground GND; let C1 ═ C3 ═ C, ReqIs the value of R1 in parallel with R2, BW represents the bandwidth of the filter circuit, fcRepresenting the set center frequency, and setting Q to represent the quality factor, the following equation is obtained:
Figure BDA0002383027230000041
Figure BDA0002383027230000042
Figure BDA0002383027230000043
(3) establishing a high-precision full-wave rectifier circuit which comprises a resistor R1, a resistor R2, a resistor R7, a diode D1, a diode D2, a capacitor C2 and operational amplifier chips OA2 and OA 3; the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA2, the cathode input end of the second-order band-pass active filter circuit is connected in parallel with a capacitor C2 through a diode D1, a resistor R1 is connected to the output end and the cathode input end of the operational amplifier chip OA3, and the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA3 through a diode D2; the negative input end of the operational amplifier chip OA3 is connected to the output end of the operational amplifier chip OA3 through a resistor R2, and the positive input end of the operational amplifier chip OA3 is connected to a ground wire R7 through a resistor R7; the positive and negative power supply ends of the operational amplifier chips OA2 and OA3 are respectively connected to the positive voltage VCC and the ground GND; setting the input voltage of a high-precision full-wave rectifier circuit to V2Output voltage of V3；
1) Selecting the gain of the positive input signal:
Figure BDA0002383027230000044
2) selecting the gain of the negative input signal:
Figure BDA0002383027230000045
3) r1, R2, R7 were chosen to have the same resistance value:
R1＝R2＝R7；
4) c2 is selected based on the desired transient response.
(4) Establishing a comparator circuit which comprises a voltage stabilizing chip, an operational amplifier chip OA4, a resistor R11, a resistor R13 and a resistor R16, wherein the voltage stabilizing chip, the resistor R11, the resistor R13 and the resistor R16 are used for generating accurate and stable direct current voltage which is connected to a negative electrode voltage input end of the operational amplifier chip OA 4; the output end of the high-precision full-wave rectifier circuit is connected to the positive voltage input end of the operational amplifier chip OA 4; setting the positive input voltage of the operational amplifier chip to be VpNegative input voltage is VnThe relation between the output voltage of the voltage stabilizing chip and the negative electrode input voltage of the operational amplifier chip is as follows:
Figure BDA0002383027230000051
the duty ratio of the output waveform of the operational amplifier chip OA4 is set as D, and the relationship between the duty ratio and the positive input voltage and the negative input voltage of the operational amplifier chip is as follows:
Figure BDA0002383027230000052
(5) an isolation sampling circuit is established, wherein the isolation circuit part comprises an isolation optocoupler, a resistor R10, a resistor R14 and a resistor R8, the output end of the comparator circuit is connected with a first port of the isolation optocoupler through a resistor R10, a second port of the isolation optocoupler is connected with GND through a resistor R14, a third port of the isolation optocoupler is connected with a power supply through a resistor R8, and a fourth port of the isolation optocoupler is connected with SGND.
(6) Through the formulas and methods provided in the steps (1) to (4), the relation between the duty ratio D and the alternating current input voltage value is obtained as follows:
Figure BDA0002383027230000053
(7) when the alternating-current input voltage changes, the duty ratio of the voltage square-wave signal output by the operational amplifier chip OA4 also changes, the duty ratio is measured by the eCAP module inside the control chip, and the alternating-current input voltage value is calculated by the formula and method provided in the step (6).
Further, the operational amplifier chip OA1 is a dual-path high-speed low-noise operational amplifier with model number MC 33078; the operational amplifier chips OA2 and OA3 are two-way low-noise high-speed JFET input operational amplifiers with the model number TLE 2072; the operational amplifier chip OA4 is a low power consumption dual operational amplifier with model number LM 258.
Furthermore, the voltage stabilizing chip is a three-end adjustable shunt reference voltage source, and the model number of the voltage stabilizing chip is TL 431; the isolation optocoupler is a low profile coupler, type TLP 185.
Further, the control chip is a DSP, and the model thereof is TMS320F 28035.
Has the advantages that: compared with the prior art, the invention has the following advantages:
(1) the method avoids the situation that a single chip microcomputer is added on the primary side or an isolation sampling device with higher price is used for sampling the alternating current input voltage, reduces the hardware design difficulty and saves the design cost;
(2) compared with the method for carrying out isolation sampling by using a transformer, the method has the advantages that the isolation optocoupler is utilized to realize electrical isolation of the original secondary side, sampling deviation caused by turn-to-turn voltage change of the transformer when the load of the vehicle-mounted power supply is changed is avoided, and more accurate voltage sampling and power reduction control are realized;
(3) the second-order band-pass active filter circuit is used for filtering the alternating voltage, so that the alternating voltage signal only keeps the part of the frequency near the fundamental wave frequency of the alternating input voltage, the sine of the sampled alternating voltage signal is ensured to the greatest extent, and the result obtained when the alternating voltage value is calculated by a formula in the follow-up process is more accurate, so that the power reduction control is more accurate;
(4) the high-precision full-wave rectifier circuit is used for rectifying the alternating current signals without using a traditional diode rectification mode, and the influence of diode voltage drop on a rectification result is avoided.
Drawings
FIG. 1 is a schematic diagram of AC input voltage sampling by level;
FIG. 2 is a schematic diagram of the control system of the present invention;
FIG. 3 is an isolated AC voltage sampling circuit diagram;
fig. 4 is a waveform diagram of the conversion of an ac input voltage to a duty cycle signal.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.
As shown in fig. 2 and 3, an ac voltage sampling circuit for output power control includes an ac voltage dividing circuit, a second-order band-pass active filter circuit, a high-precision full-wave rectifier circuit, a comparator circuit and an isolation sampling circuit, wherein an ac input voltage is input to the ac voltage dividing circuit, an output of the ac voltage dividing circuit is connected to an input of the second-order band-pass active filter circuit, an output of the second-order band-pass active filter circuit is connected to an input of the high-precision full-wave rectifier circuit, an output of the high-precision full-wave rectifier circuit is connected to an input of the comparator circuit, and an output of the comparator circuit is connected to an input of the isolation sampling circuit; the isolation sampling circuit adopts optical coupling isolation.
As shown in fig. 3, the ac voltage dividing circuit includes resistors R4 and R6, the ac input voltage is connected to the resistor R4 and then connected to the ground GND through the resistor R6, and the voltage magnitude of the divided ac input voltage can be changed by changing the resistances of the resistors R4 and R6; the function of the alternating current voltage division circuit is to divide the high-voltage alternating current input into low-voltage alternating current input, so that an operational amplifier in a post-stage circuit works in a reasonable voltage range.
The second-order band-pass active filter circuit comprises resistors R3, R5 and R9, capacitors C1, C3 and C4 and an operational amplifier chip OA 1; the output voltage of the alternating current voltage division circuit is connected to R5 and then connected to the negative electrode input end (pin No. 2) of the operational amplifier chip OA1 through a capacitor C3; one end of the resistor R9 is connected to the center point of the resistor R5 and the capacitor C3, and the other end is connected to the ground GND; the output end (pin 1) of the operational amplifier chip OA1 is connected to the central point of the resistor R5 and the capacitor C3 and the negative input end of the operational amplifier chip OA1 through the capacitor C1 and the resistor R3 respectively; the positive power supply VCC is connected to the positive input end of the operational amplifier chip OA1 after being divided by resistors R12 and R15, and is connected to the ground GND through a capacitor C4; the positive and negative power supply ends of the operational amplifier chip OA1 are respectively connected to a positive voltage VCC and a ground wire GND; the upper limit cut-off frequency and the lower limit cut-off frequency of the second-order band-pass active filter circuit can be very close to each other, and the second-order band-pass active filter circuit has very strong frequency selection characteristics, so that the alternating voltage passing through the filter only keeps the part of the frequency near the fundamental wave frequency of the alternating input voltage, good sine of the subsequently sampled alternating signal is ensured, and the sampled alternating voltage value is more accurate.
The high-precision full-wave rectifier circuit comprises resistors R1, R2 and R7, diodes D1 and D2, a capacitor C2 and operational amplifier chips OA2 and OA 3; the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA2, the cathode input end of the second-order band-pass active filter circuit is connected in parallel with a capacitor C2 through a diode D1, a resistor R1 is connected to the output end and the cathode input end of the operational amplifier chip OA3, and the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA3 through a diode D2; the negative input end of the operational amplifier chip OA3 is connected to the output end of the operational amplifier chip OA3 through a resistor R2, and the positive input end of the operational amplifier chip OA3 is connected to a ground wire R7 through a resistor R7; the positive and negative power supply ends of the operational amplifier chips OA2 and OA3 are respectively connected to the positive voltage VCC and the ground GND; the high-precision full-wave rectifier circuit converts sine alternating current into direct current, the coincidence degree of the rectified output waveform and the input waveform of the high-precision full-wave rectifier circuit is higher compared with that of a general diode rectifying circuit, the output voltage of the rectifier changes linearly along with the input voltage and is distinguished from zero, and the influence of diode voltage drop on the output voltage value is avoided.
The comparator circuit comprises a voltage stabilizing chip, an operational amplifier chip OA4, resistors R11, R13 and R16, wherein the voltage stabilizing chip and the resistors R11, R13 and R16 are used for generating accurate and stable direct-current voltage which is connected to the negative voltage input end of the operational amplifier chip OA 4; the output end of the high-precision full-wave rectifier circuit is connected to the positive voltage input end of the operational amplifier chip OA 4; the positive and negative input voltages of the operational amplifier chip OA4 are compared by the operational amplifier chip, and then a square wave signal with the amplitude VCC is generated at the output end of the operational amplifier chip. The principle of the operational amplifier chip for generating square wave signals is as follows: when the anode input voltage is higher than the cathode input voltage, the operational amplifier chip outputs a high level, and when the anode input voltage is lower than the cathode input voltage, the operational amplifier chip outputs a low level. Therefore, when the alternating-current input voltage changes, the voltage value obtained after the voltage division circuit and the rectifying circuit also changes, so that the duty ratio of the square wave signal obtained by the operational amplifier chip also changes, and the function of converting the voltage signal into the duty ratio signal is realized.
The isolation circuit part in the isolation sampling circuit comprises an isolation optocoupler, resistors R10, R14 and R8, the output end of the comparator circuit is connected with the first port of the isolation optocoupler through a resistor R10, the second port of the isolation optocoupler is connected with GND through a resistor R14, the third port of the isolation optocoupler is connected with a power supply through a resistor R8, and the fourth port of the isolation optocoupler is connected with SGND. Because the primary side and the secondary side of the vehicle-mounted power supply are not grounded together, the isolation optocoupler realizes the electrical isolation of a primary side voltage signal and the secondary side control chip; the sampling part comprises a control chip and a peripheral circuit thereof, and the sampling circuit has the functions of sampling a duty ratio signal by utilizing an enhanced capture module (eCAP) module in the control chip, and calculating to obtain a primary side alternating current input voltage signal by utilizing the sampled duty ratio so as to realize the subsequent power reduction control function.
The process of converting the ac input voltage signal to the duty cycle signal is shown in fig. 4. The alternating-current input voltage signal is a sine wave, the waveform obtained through the alternating-current voltage division circuit, the second-order band-pass active filter circuit and the high-precision full-wave rectifier circuit is a sine half-wave with only a positive half cycle, and the sine half-wave is compared with a fixed voltage value to obtain a duty ratio signal so as to be sampled through the control chip.
A design method of an alternating voltage sampling circuit for output power control comprises the following steps:
step 1: establishing an alternating current voltage division circuit which comprises resistors R4 and R6, wherein alternating current input voltage is connected to a resistor R4 and then connected to a ground wire GND through a resistor R6, and the voltage of the alternating current input voltage after voltage division can be changed by changing the resistance values of resistors R4 and R6; setting the resistances of the resistors R4 and R6 as R4 and R6, respectively, and setting the voltage obtained by the ac voltage divider circuit as V1, the following equations can be obtained:
voltage V obtained by AC voltage-dividing circuit1And an alternating current input voltage VinThe relationship of (1) is:
Figure BDA0002383027230000081
step 2: establishing a second-order band-pass active filter circuit which comprises resistors R3, R5 and R9, capacitors C1, C3 and C4 and an operational amplifier chip OA 1; the output voltage of the alternating current voltage division circuit is connected to R5 and then connected to the negative electrode input end (pin No. 2) of the operational amplifier chip OA1 through a capacitor C3; one end of the resistor R9 is connected to the center point of the resistor R5 and the capacitor C3, and the other end is connected to the ground GND; the output end (pin 1) of the operational amplifier chip OA1 is connected to the central point of the resistor R5 and the capacitor C3 and the negative input end of the operational amplifier chip OA1 through the capacitor C1 and the resistor R3 respectively; the positive power supply VCC is connected to the positive input end of the operational amplifier chip OA1 after being divided by resistors R12 and R15, and is connected to the ground GND through a capacitor C4; the positive and negative power supply ends of the operational amplifier chip OA1 are respectively connected to a positive voltage VCC and a ground wire GND; the resistances of the resistors R3, R5 and R9 are set as R3, R5 and R9, the capacitances of the capacitors C1, C3 and C4 are set as C1, C3 and C4, C1 is set as C3, and R5 is set as C4eqIs the value of R1 in parallel with R2, BW represents the bandwidth of the filter circuit, fcRepresenting the set center frequency, i.e., 50Hz, and setting Q to represent the quality factor, the following equation can be obtained:
Figure BDA0002383027230000091
Figure BDA0002383027230000092
Figure BDA0002383027230000093
the value of R3 can be made much larger than ReqTo obtain a larger Q value. The larger the Q value is, the better the frequency selection characteristic is;
and step 3: establishing a high-precision full-wave rectifier circuit which comprises resistors R1, R2 and R7, diodes D1 and D2, a capacitor C2 and operational amplifier chips OA2 and OA 3; the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA2, the cathode input end of the second-order band-pass active filter circuit is connected in parallel with a capacitor C2 through a diode D1, a resistor R1 is connected to the output end and the cathode input end of the operational amplifier chip OA3, and the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA3 through a diode D2; the negative input end of the operational amplifier chip OA3 is connected to the output end of the operational amplifier chip OA3 through a resistor R2, and the positive input end of the operational amplifier chip OA3 is connected to a ground wire R7 through a resistor R7; the positive and negative power supply ends of the operational amplifier chips OA2 and OA3 are respectively connected to the positive voltage VCC and the ground GND; setting the input voltage of a high-precision full-wave rectifier circuit to V2Output voltage of V3The resistances of the resistors R1, R2 and R7 are set to be R1, R2 and R7, and the capacitance value of the capacitor C2 is set to be C2.
1) Selecting the gain of the positive input signal:
Figure BDA0002383027230000094
2) selecting the gain of the negative input signal:
Figure BDA0002383027230000095
3) r1, R2, R7 were chosen to have the same resistance value:
R1＝R2＝R7(7)；
4) selecting C2 based on the desired transient response;
care needs to be taken in building high precision full wave rectifiers to select operational amplifiers with sufficient bandwidth and high slew rate, and if higher precision needs to be achieved operational amplifiers with low offset voltage, low noise and low Total Harmonic Distortion (THD) are used, resistors with 0.1% tolerance are selected in the design to reduce gain error, and diodes are selected to switch fast.
And 4, step 4: establishing comparator circuits, including voltage regulationThe chip, the operational amplifier chip OA4, resistance R11, R13, R16. The voltage stabilizing chip and the resistors R11, R13 and R16 are used for generating accurate and stable direct-current voltage, and the direct-current voltage is connected to the negative electrode voltage input end of the operational amplifier chip OA 4; the output end of the high-precision full-wave rectifier circuit is connected to the positive voltage input end of the operational amplifier chip OA 4; setting the resistance values of the resistors R11, R13 and R16 as R11, R13 and R16, and setting the input voltage of the anode of the operational amplifier chip as VpNegative input voltage is VnThe relation between the output voltage of the voltage stabilizing chip and the negative electrode input voltage of the operational amplifier chip is as follows:
Figure BDA0002383027230000101
the duty ratio of the output waveform of the operational amplifier chip OA4 is set as D, and the relationship between the duty ratio and the positive input voltage and the negative input voltage of the operational amplifier chip is as follows:
Figure BDA0002383027230000102
and 5: establishing an isolation sampling circuit, wherein the isolation circuit part comprises an isolation optocoupler, resistors R10, R14 and R8, and the isolation optocoupler realizes the electrical isolation of a primary voltage signal and a secondary control chip because the primary side and the secondary side of the vehicle-mounted power supply are not in common; the sampling part comprises a control chip and a peripheral circuit thereof, and the sampling circuit has the functions of sampling a duty ratio signal by utilizing an enhanced capture module (eCAP) module in the control chip, and calculating to obtain a primary side alternating current input voltage signal by utilizing the sampled duty ratio so as to realize the subsequent power reduction control function.
Step 6: through the formulas and methods provided in the steps 1 to 4, the relation between the duty ratio D and the AC input voltage value is obtained as follows:
Figure BDA0002383027230000103
and 7: when the ac input voltage changes, for example, the ac input voltage decreases, the duty ratio of the voltage square wave signal output by the operational amplifier chip OA4 also decreases, the duty ratio is measured by the eCAP module inside the control chip, and the ac input voltage value is calculated by the formula and method provided in step 6.
Preferably, the operational amplifier chip OA1 is a two-way high-speed low-noise operational amplifier with model number MC 33078;
preferably, the operational amplifier chips OA2 and OA3 are two-way low-noise high-speed JFET input operational amplifiers, and the type thereof is TLE 2072;
preferably, the operational amplifier chip OA4 is a low power consumption dual operational amplifier, whose model is LM 258;
preferably, the voltage stabilizing chip is a three-terminal adjustable shunt reference voltage source, and the model number of the voltage stabilizing chip is TL 431;
preferably, the isolation optocoupler is a low-profile coupler, the model of which is TLP 185;
preferably, the control chip is a DSP, and the model thereof is TMS320F 28035.
The invention relates to a method for controlling output power of a vehicle-mounted charger according to the magnitude of input voltage after sampling alternating current input voltage when the input voltage is lower than a certain value. For example, when the input voltage is 200V, the power is reduced until the input voltage is 80V, and the vehicle-mounted power supply is in a linear power reduction state between 200V and 80V. The general high-power vehicle-mounted power supply is provided with a Power Factor Correction (PFC) circuit, and partial power can be output after boosting when the input voltage is 90V. A power reduction method comprises the following steps: the power down is started when the input voltage is less than 200V. When the input voltage is equal to 90V, the output power is 25% of the total power; the output power is reduced by 75%/(200-90) — 0.655% when the input voltage is reduced by 1V; the invention aims to solve the problem that the sampling of the alternating-current input voltage is realized by converting the alternating-current input voltage signal into the duty ratio signal under the condition that a primary side does not have a single chip microcomputer or an expensive isolation sampling device is not used, and the invention has the advantages of low price, good real-time performance and the like.
The invention relates to an alternating current voltage sampling circuit and a design method for output power control, which solve the technical defects of input voltage sampling delay and inaccurate sampling result, and avoid the cost increase caused by adding a singlechip on a primary side for sampling and then transmitting to a secondary side or using a voltage-frequency conversion chip with higher price.

Claims (10)

1. The utility model provides an alternating voltage sampling circuit for output power control, its characterized in that, including alternating voltage divider circuit, second order band-pass active filter circuit, high accuracy full wave rectifier circuit, comparator circuit and isolation sampling circuit, wherein the input alternating voltage bleeder circuit, alternating voltage divider circuit output is connected with second order band-pass active filter circuit input, second order band-pass active filter circuit output is connected with high accuracy full wave rectifier circuit input, high accuracy full wave rectifier output is connected with comparator circuit input, comparator circuit output is connected with isolation sampling circuit input.
2. The alternating voltage sampling circuit for output power control as claimed in claim 1, wherein the alternating voltage dividing circuit comprises a resistor R4 and a resistor R6, the alternating input voltage is connected to the resistor R4 and then connected to the ground GND through a resistor R6, and the central points of the resistor R4 and the resistor R6 are connected with the input end of the second-order band-pass active filter circuit; the voltage of the divided AC input voltage can be changed by changing the resistance values of the resistor R4 and the resistor R6.
3. The alternating current voltage sampling circuit for output power control as claimed in claim 1, wherein the second-order band-pass active filter circuit comprises a resistor R3, a resistor R5, a resistor R9, a capacitor C1, a capacitor C3, a capacitor C4 and an operational amplifier chip OA 1; the output voltage of the alternating current voltage division circuit is connected to a resistor R5 and then connected to the negative input end of an operational amplifier chip OA1 through a capacitor C3; one end of the resistor R9 is connected to the center point of the resistor R5 and the capacitor C3, and the other end is connected to the ground GND; the output end of the operational amplifier chip OA1 is connected to the central points of the resistor R5 and the capacitor C3 and the negative input end of the operational amplifier chip OA1 through a capacitor C1 and a resistor R3 respectively; the positive power supply VCC is connected to the positive input end of the operational amplifier chip OA1 after being divided by the resistor R12 and the resistor R15, and is connected to the ground GND through the capacitor C4; the positive and negative power supply terminals of the operational amplifier chip OA1 are connected to the positive voltage VCC and the ground GND, respectively.
4. The alternating current voltage sampling circuit for output power control as claimed in claim 1, wherein the high precision full wave rectifier circuit comprises a resistor R1, a resistor R2, a resistor R7, a diode D1, a diode D2, a capacitor C2 and operational amplifier chips OA2 and OA 3; the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA2, the cathode input end of the second-order band-pass active filter circuit is connected in parallel with a capacitor C2 through a diode D1, a resistor R1 is connected to the output end and the cathode input end of the operational amplifier chip OA3, and the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA3 through a diode D2; the negative input end of the operational amplifier chip OA3 is connected to the output end of the operational amplifier chip OA3 through a resistor R2, and the positive input end of the operational amplifier chip OA3 is connected to a ground wire R7 through a resistor R7; the positive and negative power supply ends of the operational amplifier chips OA2 and OA3 are respectively connected to the positive voltage VCC and the ground GND; the high-precision full-wave rectifier circuit converts sinusoidal alternating current into direct current.
5. The ac voltage sampling circuit of claim 1, wherein the comparator circuit comprises a voltage stabilizing chip, an operational amplifier chip OA4, a resistor R11, a resistor R13 and a resistor R16, the voltage stabilizing chip and the resistor R11, the resistor R13 and the resistor R16 are used for generating a precise and stable dc voltage, and the dc voltage is connected to the negative voltage input terminal of the operational amplifier chip OA 4; the output end of the high-precision full-wave rectifier circuit is connected to the positive voltage input end of the operational amplifier chip OA 4; the positive and negative input voltages of the operational amplifier chip OA4 are compared by the operational amplifier chip, and then a square wave signal with the amplitude VCC is generated at the output end of the operational amplifier chip.
6. The alternating current voltage sampling circuit for output power control according to claim 1, wherein the isolation circuit part in the isolation sampling circuit comprises an isolation optocoupler, a resistor R10, a resistor R14 and a resistor R8, an output end of the comparator circuit is connected with a first port of the isolation optocoupler through a resistor R10, a second port of the isolation optocoupler is connected with GND through a resistor R14, a third port of the isolation optocoupler is connected with a power supply through a resistor R8, and a fourth port of the isolation optocoupler is connected with SGND.
7. A design method of an alternating voltage sampling circuit for output power control is characterized in that: the method comprises the following design steps:
(1) establishing an alternating current voltage dividing circuit which comprises a resistor R4 and a resistor R6, wherein alternating current input voltage is connected to a resistor R4 and then connected to a ground wire GND through a resistor R6, and the voltage of the alternating current input voltage after voltage division can be changed by changing the resistance values of the resistor R4 and the resistor R6; setting the voltage obtained by the AC voltage divider circuit to V1Voltage V obtained by an AC voltage divider circuit1And an alternating current input voltage VinThe relationship of (1) is:
Figure FDA0002383027220000021
(2) establishing a second-order band-pass active filter circuit which comprises a resistor R3, a resistor R5, a resistor R9, a capacitor C1, a capacitor C3, a capacitor C4 and an operational amplifier chip OA 1; the output voltage of the alternating current voltage division circuit is connected to a resistor R5 and then connected to the negative input end of an operational amplifier chip OA1 through a capacitor C3; one end of the resistor R9 is connected to the center point of the resistor R5 and the capacitor C3, and the other end is connected to the ground GND; the output end of the operational amplifier chip OA1 is connected to the central points of the resistor R5 and the capacitor C3 and the negative input end of the operational amplifier chip OA1 through a capacitor C1 and a resistor R3 respectively; the positive power supply VCC is connected to the positive input end of the operational amplifier chip OA1 after being divided by resistors R12 and R15, and is connected to the ground GND through a capacitor C4; the positive and negative power supply ends of the operational amplifier chip OA1 are respectively connected to a positive voltage VCC and a ground wire GND; let C1 ═ C3 ═ C, ReqIs the value of R1 in parallel with R2, BW represents the bandwidth of the filter circuit, fcRepresenting the set center frequency, and setting Q to represent the quality factor, the following equation is obtained:
Figure FDA0002383027220000022
Figure FDA0002383027220000023
Figure FDA0002383027220000031
(3) establishing a high-precision full-wave rectifier circuit which comprises a resistor R1, a resistor R2, a resistor R7, a diode D1, a diode D2, a capacitor C2 and operational amplifier chips OA2 and OA 3; the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA2, the cathode input end of the second-order band-pass active filter circuit is connected in parallel with a capacitor C2 through a diode D1, a resistor R1 is connected to the output end and the cathode input end of the operational amplifier chip OA3, and the output end of the second-order band-pass active filter circuit is connected to the anode input end of the operational amplifier chip OA3 through a diode D2; the negative input end of the operational amplifier chip OA3 is connected to the output end of the operational amplifier chip OA3 through a resistor R2, and the positive input end of the operational amplifier chip OA3 is connected to a ground wire R7 through a resistor R7; the positive and negative power supply ends of the operational amplifier chips OA2 and OA3 are respectively connected to the positive voltage VCC and the ground GND; setting the input voltage of a high-precision full-wave rectifier circuit to V2Output voltage of V3；
1) Selecting the gain of the positive input signal:
Figure FDA0002383027220000032
2) selecting the gain of the negative input signal:
Figure FDA0002383027220000033
3) r1, R2, R7 were chosen to have the same resistance value:
R1＝R2＝R7；
4) selecting C2 based on the desired transient response;
(4) establishing a comparator circuit which comprises a voltage stabilizing chip, an operational amplifier chip OA4, a resistor R11, a resistor R13 and a resistor R16, wherein the voltage stabilizing chip, the resistor R11, the resistor R13 and the resistor R16 are used for generating accurate and stable direct current voltage which is connected to a negative electrode voltage input end of the operational amplifier chip OA 4; the output end of the high-precision full-wave rectifier circuit is connected to the positive voltage input end of the operational amplifier chip OA 4; setting the positive input voltage of the operational amplifier chip to be VpNegative input voltage is VnThe relation between the output voltage of the voltage stabilizing chip and the negative electrode input voltage of the operational amplifier chip is as follows:
Figure FDA0002383027220000034
the duty ratio of the output waveform of the operational amplifier chip OA4 is set as D, and the relationship between the duty ratio and the positive input voltage and the negative input voltage of the operational amplifier chip is as follows:
Figure FDA0002383027220000041
(5) establishing an isolation sampling circuit, wherein the isolation circuit part comprises an isolation optocoupler, a resistor R10, a resistor R14 and a resistor R8, the output end of the comparator circuit is connected with a first port of the isolation optocoupler through a resistor R10, a second port of the isolation optocoupler is connected with GND through a resistor R14, a third port of the isolation optocoupler is connected with a power supply through a resistor R8, and a fourth port of the isolation optocoupler is connected with SGND;
(6) through the formulas and methods provided in the steps (1) to (4), the relation between the duty ratio D and the alternating current input voltage value is obtained as follows:
Figure FDA0002383027220000042
(7) when the alternating-current input voltage changes, the duty ratio of the voltage square-wave signal output by the operational amplifier chip OA4 also changes, the duty ratio is measured by the eCAP module inside the control chip, and the alternating-current input voltage value is calculated by the formula and method provided in the step (6).
8. The method of claim 7, wherein the method further comprises: the operational amplifier chip OA1 is a two-way high-speed low-noise operational amplifier with model number MC 33078; the operational amplifier chips OA2 and OA3 are two-way low-noise high-speed JFET input operational amplifiers with the model number TLE 2072; the operational amplifier chip OA4 is a low power consumption dual operational amplifier with model number LM 258.
9. The method of claim 7, wherein the method further comprises: the voltage stabilizing chip is a three-end adjustable shunt reference voltage source, and the model number of the voltage stabilizing chip is TL 431; the isolation optocoupler is a low profile coupler, type TLP 185.
10. The method of claim 7, wherein the method further comprises: the control chip is a DSP, and the model number of the control chip is TMS320F 28035.
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