CN113866492A - Linear isolation sampling method for direct-current voltage signal - Google Patents

Abstract

The invention discloses a linear isolation sampling method of a direct-current voltage signal, which comprises the following steps: the method comprises the following steps: attenuating a voltage VDC to be tested into a low voltage after voltage division by R26 and R29, and sending the low voltage to a dimming input port of U4, wherein U4 is a dimming chip, and the VDC is a voltage signal to be tested; step two: u4 outputs square waves of relative duty ratio at pin 6 according to the voltage value sent to pin 5; step three: the square wave signal drives the optocoupler U5, and isolated transmission of the sampling signal is realized at a pin 3 of U5; step four: the sampling signal Vs is introduced into an MCUCAP port to carry out time calculation, square wave war space ratio is calculated, or the sampling signal Vs is converted into direct current voltage after low-pass filtering and is directly sent to an AD channel, and then the actual voltage value of VDC can be sampled. Compared with the prior art, the invention has the advantages that: the device has the advantages of few elements, simplicity, easy use, long service life, strong anti-interference performance, high isolation voltage, low cost and the like.

Description

Linear isolation sampling method for direct-current voltage signal

Technical Field

The invention relates to the technical field of voltage signal sampling methods, in particular to a linear isolation sampling method for a direct-current voltage signal.

Background

In order to meet the market demand of power supply products, input and output isolation, alternating current and direct current isolation or isolation of a power circuit and a control circuit is adopted by designers more and more. The isolated sampling of direct-current voltage signals such as battery voltage or bus voltage and the like has important significance on the performance of power supply products, the anti-interference of a control system, even the application of some circuit topologies and the realization of product design schemes.

Generally, there are several existing electrically isolated sampling schemes:

using linear optocouplers

The scheme has the defects of high cost, complex circuit and the like. The linear optocoupler is expensive, and circuit elements such as a peripheral operational amplifier and the like which must be matched also increase the use cost and the circuit complexity.

Using isolated operational amplifiers

The scheme adopts a novel isolation operational amplifier (isolation operational amplifier) in the field of semiconductors, and compared with a linear optical coupler, an application circuit is simple. However, due to newly-built devices, the isolation operational amplifier is high in price and long in purchase period, and is not beneficial to popularization and use; and the static voltage output by the isolation operational amplifier is usually a fixed value, and for sampling direct current voltage, the resolution of an AD channel is wasted by the static output voltage, and the sampling precision is reduced.

Using self-oscillating circuits

The scheme applies the saturation characteristic of an isolation transformer to enable triodes to be conducted alternately, and two windings on the primary side of the transformer are used for respectively transmitting energy and realizing magnetic reset. The main disadvantage of the scheme is poor sampling linearity and temperature characteristics; and because the transformer can saturate during operation, in order to prevent the triode from overcurrent, a current-limiting resistor needs to be connected in series at the input end. When higher voltage needs to be sampled, the current-limiting resistor has large power consumption and serious heat generation.

Disclosure of Invention

The invention aims to overcome the technical defects and provides a linear isolation sampling method for a direct-current voltage signal.

In order to solve the technical problems, the technical scheme provided by the invention is as follows: a linear isolation sampling method for direct-current voltage signals comprises the following steps:

the method comprises the following steps: attenuating a voltage VDC to be tested into a low voltage after voltage division by R26 and R29, and sending the low voltage to a dimming input port of U4, wherein U4 is a dimming chip, and the VDC is a voltage signal to be tested;

step two: u4 outputs square waves of relative duty ratio at pin 6 according to the voltage value sent to pin 5;

step three: the square wave signal drives the optocoupler U5, and isolated transmission of the sampling signal is realized at a pin 3 of U5;

step four: the sampling signal Vs is introduced into an MCU CAP port to carry out time calculation, square wave war space ratio is calculated, or the sampling signal Vs is converted into direct current voltage after low-pass filtering and is directly sent to an AD channel, and then the actual voltage value of VDC can be sampled.

Compared with the prior art, the invention has the advantages that: 1. the method has wide applicability in the field of isolation sampling of direct-current voltage, and can be used for acquiring direct-current signals of any voltage by only selecting a proper divider resistor and attenuating the voltage into the input voltage range of the dimming IC;

2. the output signal is linearly related to the sampling signal, so that the sampling precision and the temperature stability are good;

3. the device has the advantages of few elements, simplicity, easy use, long service life, strong anti-interference performance, high isolation voltage, low cost and the like.

Drawings

Fig. 1 is a circuit diagram of a linear isolation sampling method for dc voltage signals according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention discloses a linear isolation sampling method of a direct-current voltage signal, which comprises the following steps:

the method comprises the following steps: attenuating a voltage VDC to be tested into a low voltage after voltage division by R26 and R29, and sending the low voltage to a dimming input port of U4, wherein U4 is a dimming chip, and the VDC is a voltage signal to be tested;

step two: u4 outputs square waves of relative duty ratio at pin 6 according to the voltage value sent to pin 5;

step three: the square wave signal drives the optocoupler U5, and isolated transmission of the sampling signal is realized at a pin 3 of U5;

step four: the sampling signal Vs is introduced into an MCU CAP port to carry out time calculation, square wave war space ratio is calculated, or the sampling signal Vs is converted into direct current voltage after low-pass filtering and is directly sent to an AD channel, and then the actual voltage value of VDC can be sampled.

With the increasingly widespread use of LED lighting in life, various matched LED driving power supplies have also been designed, and dimming becomes a basic function of LED power supplies. At present, a plurality of cheap and reliable dimming chips are available on the market for selection, PWM waves with variable duty ratios can be output according to different output voltages, and considerable linearity is achieved within a certain range.

The invention is provided based on the linear relation between the input voltage of the dimming chip and the duty ratio of the output PWM wave. Direct current voltage to be sampled is divided by a high-precision resistor and then led to a dimming chip, square waves output by the chip are connected to a primary side of an optocoupler and can be transmitted to a secondary side of the optocoupler without distortion, and electrical isolation is achieved; the isolated square wave signal can be sent to a capture unit (CAP unit) of a signal processing chip such as an MCU (microprogrammed control Unit), the duty ratio of the square wave is directly calculated, or a direct current signal is converted into a direct current signal by resistance-capacitance low-pass filtering and sent to an analog-digital conversion channel (AD energy channel) of the MCU, and the electric isolation sampling of the direct current voltage is realized by calculating the duty ratio or a voltage value.

The PWM wave frequency output by the dimming chip can be usually set at a lower frequency, so that no special requirement is imposed on the isolation optocoupler, and the most common low-speed optocoupler can meet the design requirement; the output is a digital signal, and the dry-pull resistance is strong; the change of the temperature positively affects the frequency of the PWM wave and the time of the high level, although the frequency has temperature drift, the duty ratio basically does not change along with the temperature, and therefore, the PWM wave has good temperature characteristics.

Abandon traditional high-priced linear opto-coupler or keep apart operational amplifier, but adopted low cost's dimming chip and ordinary opto-coupler to realize the sampling: the linear relation between the input voltage and the output square wave duty ratio of the light modulation chip is utilized to divide the direct current voltage to be sampled into small signals and then the small signals are sent to the light modulation IC, the square waves output by the IC are isolated and restored by the optical coupler, and the accurate sampling value can be obtained by the MCU software calculation method, so that the linear isolation sampling of the direct current voltage can be realized by using a small amount of low-price components.

The dimming chip in the circuit has various choices in the market, and has stable performance and low price; the optical coupler is only used for isolating low-speed digital signals, so that no special requirement exists, and the most common optical coupler can meet the requirement.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims (1)

1. A linear isolation sampling method for direct current voltage signals is characterized by comprising the following steps: the method comprises the following steps:

the method comprises the following steps: attenuating a voltage VDC to be tested into a low voltage after voltage division by R26 and R29, and sending the low voltage to a dimming input port of U4, wherein U4 is a dimming chip, and the VDC is a voltage signal to be tested;

step two: u4 outputs square waves of relative duty ratio at pin 6 according to the voltage value sent to pin 5;

step three: the square wave signal drives the optocoupler U5, and isolated transmission of the sampling signal is realized at a pin 3 of U5;

step four: the sampling signal Vs is introduced into an MCU CAP port to carry out time calculation, square wave war space ratio is calculated, or the sampling signal Vs is converted into direct current voltage after low-pass filtering and is directly sent to an AD channel, and then the actual voltage value of VDC can be sampled.

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