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Please remember these 4 points to switch power supply in order to "comply with safety regulations".


01 Safety Introduction

1. Definition

Rules adopted to protect personal safety, property, environment, etc. from harm and loss.

2. Safety requirements

a. electric shock

b. Fire

c. Electromagnetic radiation

g. Environmental pollution

d. Chemical radiation

e. Energy Shock

w. Chemical corrosion

s. Mechanical damage and thermal damage

3. Basic global safety standards

a.IEC system - represented by European Union

b.UL system----represented by USA

Even though two systems are independent, there is a tendency to recognize each other and strive for consistency.

4. Safety Certification

Security certification is actually a technical barrier. Different countries around world have different requirements for safety regulations to restrict importation of goods from other countries into their countries, and they are mandatory.

General Safety Certification:


b.TUV, VDE, GS-Germany



e.CE-European Union


g. --Denmark

h. --Norway

i. --Finland

to. --Sweden

In addition, there are Australia, New Zealand, Singapore and other countries.

02 Safety Certification Application Process

1. Submit application materials to security agency.

2. The Safety Certification Agency will respond within promised time as to whether application should be accepted.

3. After security agency accepts application, applicant starts submitting samples for security testing.

4. If sample passes safety test, safety certification body arranges a factory inspection (UL called IPI), if sample fails test, it is returned to applicant and applicant fails test. Make adjustments , and then re-submit sample for testing. If it fails second time, you need to re-apply.

5. After passing factory inspection, safety certification body issues a certification certificate or power of attorney to use safety mark, and applicant can use certification body's mark on certified product. If factory inspection is not passed, certification body gives applicant time to correct and reform and re-inspect after correction is completed. If re-inspection is not passed, applicant must re-apply.

6. In future, certification bodies will conduct additional checks on certified products.production. As a general rule, UL conducts inspections four times a year, CCC conducts inspections once a year, and most other certification bodies conduct inspections once a year. Follow-up inspection mainly checks conformity of product, but CCC, TUV, etc. also check quality system.

03 Basic requirements for safety regulations for electronic products

1.Withstand voltage (dielectric strength) - to prevent electric shock

2.Insulation resistance - to prevent electric shock

3.Ground resistance - to prevent electric shock

4.Leakage Current - Prevention of Electric Shock

5.EMC - ability to withstand electromagnetic interference and interference with other electronic products

6.Fire resistant - prevents fire hazards

7.Mechanical design - to prevent damage, burns, etc. caused by mechanical design defects

8.Energy impact - prevent fire or arc burns caused by high current

04 Safety requirements for electronic products during production

1. Withstand Voltage. The focus is on ability of insulation system to withstand abnormally high product voltages. The operating voltage is lower than 50V, and voltage withstand test is generally not performed.

a. The withstand voltage is usually related to operating voltage of product.

Commonly used calculation formula:

1) AC: 1000 2* rated operational voltage

2) DC (1000 2*rated operating voltage)*1.4

The above test voltage is for normal insulation. If it is double insulation, test voltage is twice normal voltage.

If computed result is not an integer multiple of 100, greater is taken, not less.

Example: rated operational voltage 220 V, test voltage of ordinary insulation:

AC: 1000 2*220=1440V, at this time, test voltage should be 1500V instead of rounding.

b. Setting leakage current

The general setting is 5~10mA, and maximum value does not exceed 100mA. Different industries have different requirements. For example, leakage current of medical equipment is typically 1mA.

c. Setting test time

The total test duration is set to 1 minute, which can be shortened on production line, but total ramp-up time must not be less than 1 second. If test time is shortened, a higher test voltage should be used. According to UL rules, following relationships can be converted:

AC (1000V 2*ratedoperating voltage)*1.2

DC (1000V 2*rated operating voltage)*1.4*1.2

2. Insulation resistance. The focus is on insulating performance of product

The insulation resistance test voltage generally takes DC voltage, typically 500V, insulation resistance is at least 10MΩ, and test time is typically 1 minute. If test time needs to be shortened, it can be adjusted by referring to voltage withstand test.

3. Leakage current. The main consideration is leakage current to earth or contact interface caused by distributed capacitance or insulation characteristics of product at maximum operating voltage and maximum operating current, which is due to insulation of product.

The maximum leakage current limit is typically 1 mA. The testing time is usually 1 minute.

4. Ground resistance. The focus is on ability of a product insulation breakdown or charge leakage under normal operating conditions to quickly direct these charges to ground. measure Not taken into account in products that are not grounded.

The lower ground resistance, better. The total unit ground resistance must not exceed 0.1 Ω, total system ground resistance must not exceed 4 Ω, and continuity resistance between ground points in system cannot exceed 0.01 Ω.

According to experience, if voltage withstand test is passed, insulation resistance test will generally be passed, but insulation resistance test is passed, but this does not mean that voltage withstand test will also be passed.

In case of mass production, production line generally only needs to check withstand voltage, and insulation resistance, leakage current, and earth resistance are only checked during spot checks.

5. Safety distance

Safety distance includes creepage distance and electrical clearance.

The creepage distance is shortest distance along an insulating surface between live conductors.

Gap is shortest distance in space between live conductors.

The safety distance is one of guarantees of withstand voltage, insulation resistance and leakage current.

The minimum safety distance depends on operating voltage of product. See table below.

6. Electromagnetic compatibility

EMC requires many test items and general requirements are:

a. Conducted Emissions and Immunity

b. Radiation interference and anti-jamming

in. Antistatic

g. Lightning protection

e. Surge protection or surge protection, etc.

Due to conducted and radiated interference, specialtest equipment is large, large and complex, and regular spot checks are usually used and are assigned to competent testing agencies.

Electromagnetic compatibility has now become an extremely important requirement of safety regulations, many countries have included it in list of mandatory items and independently carry out electromagnetic compatibility certification - EMC certification.

7. Fire resistance

It is necessary that product itself cannot ignite and burn, and it can burn together in presence of an external fire source, but as soon as external fire source is gone, product must stop burning immediately. V-0 products in UL94.

8. Structural mechanical damage and thermal damage

Due to structural defects of electronic products, such as sharp edges, sharp corners and burrs, it is easy to harm human body, and if hole is too large or safety distance is not enough, it is easy to touch internal live parts and cause electric shock, and protective measures are wrong. Moving parts can harm human body, and wrong heat dissipation measures can easily burn human body.

Generally speaking, in large-scale production, in addition to online testing of withstand voltage and insulation resistance, other items are subject to regular spot checks or external tests. CCC certification stipulates that products must undergo regular confirmatory testing at least once a year. once.

9. General safety components for electronic products

a. Fuse

b. Wire

Condenser c.X and capacitor Y

g. High Voltage Capacitor

e.g. transformer, inductor

e. Varistor

w. Plastic parts

h. Insulation pad


j.Model label or nameplate

l. Warning signs

1. Optocoupler


p. cooling fan

Security components are one of key controls of security certification bodies. Any safety certification body issues a list of safety critical parts for certified products, and safety certification bodies conduct reviews based on this list. Consistency check. who specify specifications and manufacturers in list must use specified manufacturers and specifications. Those who do not specify a manufacturer, but specify specifications and models, may also specify a requirement to obtain appropriate certification. Use specified specifications and models, and you need to obtain appropriate certification. If parts important to safety are changed, you must apply for a report to a safety certification agency.sti.Only after receiving approval and approval, you can change, and sometimes you have to resubmit test sample, and test is passed, only then can you make official changes.