Safety Distance Design Solution for Miniature All-rounder AC/DC Converter LS Series
CONTENTS
2. Common Questions about Safety Distance Issues of LS Series
Abstract:
In this paper, we briefly describe the safety distance issues encountered by customers during the use of the Mornsun AC/DC power supply LS series, sort out these issues and propose corresponding solutions so that customers can use the LS series more conveniently.
Keywords:
AC/DC converter, LS series, safety distance, creepage distance
1. Introduction
As technology continues to improve, the size of products becomes increasingly demanding. Mornsun has introduced the ultra-miniature AC/DC power supply - LS series. It is convenient for customers to design the overall layout of the system flexibly. However, some customers may have questions about the safety distance and design. To address customer confusion, this paper aggregates typical questions often encountered and provides the analysis and proposed solutions.
2. Common Questions about Safety Distance Issues of LS Series
① Is there a safety distance requirement between pins 1 and 2 of the LS series?
② Should the AC(L) pin and AC(N) pin be kept at a safety distance from other devices in the high-voltage area?
③ What distance must be maintained between the primary and secondary (pins 4 and 5) and how should this be designed?
Pic.1 Pin layout of LS series
3. Take LS05-13B03R3 as an example for Analysis
1) Product introduction:
Pic.2 Pins’ function of LS series
2) Analysis
① Is there a safety distance requirement between pins 1 and 2 of the LS series?
A fuse must be added to the L line when using the LS product, so there is no safety distance requirement for the devices and pins behind the fuse, we can just leave enough distance (functional insulation) according to the actual voltage difference between high and low voltage.
Pic 3. Recommended pad for LS05 series
② Should the AC(L) pin and AC(N) pin be kept at a safety distance from other devices in the high-voltage area?
Pins 1 and 2 of the LS series are different from AC(L) and AC(N). The AC(L) and AC(N) pins are directly connected to the AC current from the gird, and according to the safety standards (e.g., IEC 62368), the front and rear high voltage zones of fuses connected to the AC grid need to be maintained at a safety distance of basic insulation.
Pic 4. Safety Distance Design Simple Diagram between AC(L) and AC(N)
③ What distance must be maintained between the primary and secondary (pins 4 and 5) and how should this be designed?
Pins 4 and 5 are the primary and secondary sides. The standard safety clearance requirements for AC/DC products, under normal working voltage, are as follows: electrical clearance of 4mm and creepage distance of 6.4mm. The LS products are designed to meet this general requirement. However, if the operating voltage is lower, customers can refer to Chapter 5 of IEC62368 for design guidance.
If the creepage distance on the PCB is insufficient, a slot can be made to provide the required clearance. As shown in the figure below, the slot between the two pins (must be greater than 1mm) is to increase the creepage distance. This is just one of the ways to meet the safety distance, and we can choose another way to increase the creep distance depending on the actual application.
Pic 5. Example for slotting to increase safety clearance
4. Summary
Safety distance is an important design parameter that must be considered at the beginning of the design process and directly affects the layout of the entire product layout. This paper recommends a number of methods to help select better and better design solutions for smooth product design, but is not limited to the above recommendations, and can be specific based on the actual application to design.
