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CD4066 Quad Bilateral Switch Application Circuit

  • Contents

I Description

In data collection, when the amount of collection is relatively large, the problem of insufficient SCM resources often occurs.

In order to solve this problem, this blog combines the situation of data collection in the integrated automation system of substations and proposes a very practical method using CD4066 electronic switches.

cd4066Catalog

I Description

II Introduction

III Structure of 1CD4066 Electronic Switch

IV Design of Switching Circuit Boards in Data Acquisition Devices

V Improvement of Switching Circuit Board in Data Acquisition Device

FAQ

Ordering & Quantity

II Introduction

When collecting alternating current and voltage signals, it is generally to convert the signals to be collected into lower voltage signals through transformers (CT and PT). Then through the A/D conversion device, the analog signal is converted into a digital signal and sent to the single-chip microcomputer for collection.

But when there are more data channels that need to be collected, the situation becomes more complicated.

For example, the automatic device of the electric power system-the digital centralized measuring device needs to collect 4 groups, 8 groups, or even more power measuring points.

If each power measurement point is calculated according to two currents (such as A phase and C phase, B phase is calculated by A and C phases), three voltages (A, B, C three phases), plus part of the 3U 0 voltage (3U 0 voltage refers to the open delta voltage of the secondary winding of the transformer, which can be expressed as 3U 0 =U a +U b +U c ), it is necessary to measure dozens of currents and voltages.

If each channel of measurement is equipped with an A/D conversion device and is directly connected to the MCU plug-in, the following problems exist:

  1. The resources of the ordinary single-chip microcomputer are insufficient, and multiple single-chip microcomputer boards are needed.
  2. Many A/D conversion devices are required, which is not economical.
  3. The equipment will be huge and will not meet the requirements of increasingly miniaturized digital products.

The switchboard made of CD4066 electronic switch proposed in this blog.

Under the condition of ensuring measurement accuracy and stability, the required A/D converter and microcontroller resources can be reduced to 1/2 or 1/4 of the original.

At the same time, because the CD4066 chip is relatively cheap, the cost of the required switchboard is relatively low.

At the same time, in order to meet the requirements of measurement accuracy and stability, the following measures were taken during the design process:

(1) Use dedicated measurement-level CT and PT for the transformer of the AC plug-in (AC plug-in).

The CT measurement accuracy is high, and the current enters the linear region quickly. The phase shift of CT and PT is very small (less than 0.1 degrees), which makes the accuracy of power measurement very high.

(2) For the analog-to-digital conversion plug-in, considering the size of the board and actual application needs, 12 voltage/frequency converters with exactly the same circuit structure are used to convert the 12-way analog output of the switching plug-in into pulse frequency with input. The analog quantity of amplitude change. And after the fast optocoupler (6N137) photoelectric isolation, it is sent to the counter in the CPU system for counting to realize the analog-to-digital conversion.

The voltage/frequency converter of this plug-in adopts the third-generation VFC chip (VFC110), and the linear range of its voltage-frequency characteristic is 0~4MHz.

Compared with AD654, the highest conversion frequency of 0.5MHz is increased by 8 times, which greatly improves the accuracy of analog-to-digital conversion.

Moreover, the VFC110 chip has a high-precision biasing 5V regulated power supply on-chip, which can eliminate the need for an external bias regulated power supply and is very convenient to use.

(3) A latch 74LS374 is set for the analog input loop in the CPU plug-in, and the signal from the VFC plug-in is latched by the clock generated on the CPU chip.

One of its functions is to turn the external asynchronous pulse signal into a synchronous pulse signal, which is beneficial to combat interference;

The second function is to get the pulse shaping function. When one switching plug-in is needed, the basic implementation process of the whole measurement is shown in Figure 1. When two switching plug-ins are needed, the basic implementation process is shown in Figure 2.

Schematic diagram of data collection of one switching board

Figure 1. Schematic diagram of data collection of one switching board

Schematic diagram of data acquisition of two switching boardsFigure 2. Schematic diagram of data acquisition of two switching boards

III Structure of 1CD4066 Electronic Switch

CD4066 is an IC containing four sets of analog switches, and the chip structure is shown in Figure 3.

Structure diagram of CD4066 chip

Figure 3. Structure diagram of CD4066 chip

The so-called analog switch is a component that can use the digital signal at the control end to determine whether the analog signal at the input end can reach the output end.

CD4066 analog switch, both ends of the signal can be used as input or output. In other words, if one end is the input end, the other end is the output end. In addition, the frequency response of CD4066 is also very good, up to 1MHz or more.

Therefore, you can use CD4066 to switch and measure the four-channel analog quantity.

IV Design of Switching Circuit Boards in Data Acquisition Devices

In the actual measurement of power system substations, it is often necessary to measure the high and low voltage sides or high, medium and low voltage side power of the transformer. Each group of power points needs to measure two-phase current, three-phase voltage, and it is also possible to measure 3U0 on the main side and the voltage on the side used. Therefore, 6 CD4066 chips are arranged on one board during the design, each of which is a group of 3, and a total of 24 analog quantities can be measured.

The control ends of each group of chip switches are connected together and controlled by one single chip. Because the MCU and CD4066 work level is different. Therefore, the single-chip microcomputer should be isolated by photoelectric isolator. In this way, the 12 switches of each group of chips can be turned on and off simultaneously under the control of the single-chip microcomputer.

Under the control of the single chip microcomputer, when one way is driven high, the other way is driven low. That is, only a group of 12 analog quantities are collected each time, and the collected data is placed in different storage locations of the single-chip microcomputer for processing.

In this way, when measuring 24 analog quantities, only 12 A/D converters are needed, and only 12 analog input resources of the CPU plug-in are occupied. The price paid is only one more switching plug-in, which achieves economic and efficient goals.

Because the working voltage of CD4066 is 3~15V, in order to ensure the stability of work, we take +15V, -15V voltage and 15V ground from the power plug of the device. Supply power to the two LM7809 and LM7909 three-terminal regulators of the switching plug-in respectively, and the +8V and -8V output from them are respectively supplied to the CD4066. The schematic diagram of the entire switching plug-in is shown in Figure 4.

Switch plug-in schematicFigure 4. Switch plug-in schematic

V Improvement of Switching Circuit Board in Data Acquisition Device

In the actual use of the circuit designed according to Figure 4, some of the switches of the CD4066 chip are often damaged, resulting in no measured data or soft conduction. Unplug the chip, plug it in again or turn it off and then turn it on again, and it partially returns to normal. Later, it was replaced with a military-grade 4066 chip and found that the situation did not improve.

In this regard, we have analyzed and conducted various experiments. After the test, it is believed that the AC voltage signal converted from CT/PT sometimes has a large peak value, even exceeding the working voltage of the chip ±8V, and even exceeding the set value of the AC voltage (the set range is -5~+5V) . As a result, some electronic switches are damaged or turn on softly.

Taking into account the cost and convenience of changes, we adopted a very simple method. That is: Connect two diodes to the input of each electronic switch of CD4066. The forward input end of one diode is connected to the -8V of the three-terminal regulator LM7909, and the forward output end of the other diode is connected to the +8V of the three-terminal regulator LM7809. The input terminal voltage of each electronic switch is clamped between -8V and +8V, so as to protect each channel of the electronic switch. The specific connection is shown in Figure 5.

Schematic diagram of the improved switching plug-inFigure 5. Schematic diagram of the improved switching plug-in

At the same time, in order to prevent damage to the CD4066 chip due to the unstable output of the three-terminal regulator, a smaller resistor is connected to the VDD and VSS terminals of the chip.


FAQ

  • What is CD4066?

The CD4066 is a Quad Bilateral Switch IC, that is, it has four switches which can be controlled individual using a control pin. These switches can conduct in both the directions making it bilateral, it is commonly used for multiplexing analog or digital signals.

  • How to use CD4066?

The CD4066 IC consists of four switches. It can switch analog signals through digital control. An analog signal is applied at the input of the switch. If a HIGH or 1 value is fed into the control input, the analog signal will be passed from input to the output of a switch.

  • How CD4066 work?

The 4066 really functions as an analog switch. The 4066 is an IC composed of switches which are designed to switch analog signals via digital control. ... The 4066 is a quad bilateral switch circuit, meaning that is composed of 4 switches. Each switch has a single input and a single output terminal.

  • What are the applications of CD4066?

The CD4066 is a bi-directional analog switching IC similar to CD4016, it is commonly used in multiplexing applications; it can also be used to isolate signals. The switch is bilateral and hence can be used for both digital and analog signals.

  • What's the difference between CD4016 and CD4066?

The major difference between both is that CD4066 has very low internal resistance, according to the datasheet it can only 5Ω of on-state resistance as compared with 200Ω of CD4016 IC.

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