DC turnout represents the system's power isolation and signal isolation solutions

March 20, 2022

Background: The switch indicates that the system is a device for detecting the steering and operating current of the switch. It is one of the important components of the signal centralized monitoring system and is the guarantee for the safe operation of the railway. This article will share the application of power isolation and signal isolation solutions in DC turn-to-turn representation systems.

Figure 1. DC trace 岔 representation system block diagram

Program recommendation:

Power solution

According to the provisions of the "Signal Centralized Monitoring System Acquisition Technical Plan and Construction Process Requirements":

1) The DC switch indicates that the collector casing and package of the system should adopt the special relay housing and base of the railway signal specified by the Ministry of Railways, in accordance with the standard GB/T 7417-2001; each collector collects 4 sets of DC switch machine turns to indicate the voltage. Each group of DC converters represents the voltage representation through two groups, which respectively represent the positioning acquisition signal and the inverted acquisition signal;

2) Each group of ballast sampling lines are separated by one terminal, and the withstand voltage is above AC4000V; the spacing between the pads of different groups of ballasts is greater than 6mm. If the safety gap is not met, it is necessary to open the isolation groove with a width greater than 1mm;

3) The withstand voltage between the terminals, between the input and output, and between the input and the power supply is higher than DC2500V. For the high current between the terminals exceeding AC3000V and the current is greater than 200mA, the fuse between the high and low ends of the input circuit is disconnected, and the open circuit state is present; the high voltage part is strictly distinguished from the low voltage part wiring area, indicating the wiring interval of the voltage input part. More than 6mm.

The isolated power supply for the DC voltage representation portion of the collector must have the following characteristics:

1) Small-volume package, reducing the board volume requirement, leaving more space for the input isolation circuit to ensure the safety distance between the pads and improve the overall safety of the product;

2) High withstand voltage characteristics, meeting the requirements of 2500V isolation characteristics, can prevent the high-voltage impact such as induction lightning, locomotive over-rail, etc., and string into the measurement circuit of the latter stage to improve the module's ability to withstand high voltage;

3) Low power consumption, high efficiency requirements, 8 groups of power supplies work together, can significantly reduce the temperature rise of the product, and can reduce the power requirements of the bus power supply;

In response to this characteristic requirement, Jin Shengyang launched E_T-W2 & F_T-W2 0.25W, constant voltage input, 3000VDC isolated unregulated positive and negative dual/single output DC-DC module power supply series to solve the DC switch system voltage. The problem of power selection in the acquisition;

This power supply series has the following features:

● Small size 15.24mm*7.5mm*6.5mm;

● SMD package is more suitable for automatic patch production;

● The isolation voltage is 3000VDC, which meets the requirements of the iron standard for the ballast collection system;

● Operating temperature range: -40 ° C ~ +85 ° C, to meet the harsh outdoor working conditions;

● No need to add components to reduce PCB area and flexible application; Figure 2. Schematic diagram of F_T-W2

DC turnout represents the system's power isolation and signal isolation solutions

● International standard pin mode;

Generally, the switch indicates that the bus input voltage of the collector is 12V, and the switch indicates that the voltage is generally 0-5V or 0-10V. This signal conversion part can use the module power supply F1212T-W2 to meet the design requirements;

For the switch, the bus input power of the system acquisition box is indicated. Because each switch can only work in one of the working or reverse positions, that is, only four groups of F1212T-W2 work, and the DC-DC 3W product meets the design requirements. This bus input power supply must have a small package requirement, leaving enough space for the input isolation circuit; Jinshengyang WRF_S-3WR2 products can meet the design requirements;

2. Communication solutions

The traditional RS485 communication solution adopts optocoupler isolation and DCDC isolation self-containment scheme. Because of the large area occupied, it has limitations for the application of the DC box to indicate the collection box of the system. Therefore, it is recommended to use the Jinshengyang RS485 isolation transceiver module. The module is an interface isolation transceiver module with integrated transceiver chip, isolation chip and DC/DC isolated power supply, which can completely replace the traditional optocoupler isolation scheme. Figure 3. Schematic diagram of TDXXXD485H

DC turnout represents the system's power isolation and signal isolation solutions

● Magnetic coupling isolation technology replaces traditional optocoupler isolation technology with higher reliability;

● Modular package can reduce the PCB footprint and better meet the application of the collector;

● The isolation voltage is 2500VDC, which meets the requirements of the iron standard for communication isolation;

● Operating temperature range: -40 ° C ~ +85 ° C, to meet the harsh outdoor working conditions;

● Internal pin integrated anti-static module reduces PCB area and flexible application;

3. EMC circuit solutions

1) Switch indicates voltage input EMC circuit protection

According to the "Signal Centralized Monitoring System Acquisition Technical Plan and Construction Process Requirements", the switch indicates that the voltage input EMC protection circuit indicates the input and output parts in each group of switches. It must be connected to a 2W metal film with high withstand voltage to prevent The high-voltage part is connected to the rear-stage circuit. This high-voltage resistor can significantly reduce this high voltage. In the signal conversion part, it is necessary to string into the TVS tube. On the one hand, it can prevent the output of the DCDC power supply from being damaged due to the high-voltage input part; On the one hand, it can protect the abnormal part of the signal conversion part due to the transient high voltage.

2) EMC circuit protection of the bus power supply of the collector

Since the bus power supply of the collector is already in the secondary power supply, the protection of the surge and the group pulse on the primary power supply side has been done very well. Generally, only an electrolytic capacitor of about 47uF-100uF is connected in parallel with the input end of the bus power supply. A SMBJ TVS tube can meet the design requirements;

3) EMC circuit protection of 485 communication part

The EMC recommended circuit for the 485 module is as follows: Figure 4.485 Module Recommended Circuit

DC turnout represents the system's power isolation and signal isolation solutions