As a new energy product, switching power supply is also the heart of electrical products. If the switching power supply does not work normally, it will cause the abnormal operation of the whole electrical appliance. Here are some basic parameters of switching power supply.

1 describe several index forms of input voltage affecting output voltage

(1) voltage stabilizing coefficient

① Absolute voltage stabilizing coefficient K of switching power supply (linear adjustment rate)

Indicates the ratio of the output DC voltage change △ uo of the regulated power supply to the input grid voltage change △ UI when the load is unchanged, i.e. k = △ uo / △ UI. The general requirements for switching power supply are 3%

(2) grid adjustment rate

The grid adjustment rate of switching power supply indicates the relative change of output voltage of regulated power supply when the input grid voltage changes / - 10% from the rated value (90-264VAC), sometimes expressed as absolute value. Generally within 5%

2 several index forms of the influence of load on output voltage

(1) load regulation rate (also known as current regulation rate)

It refers to the maximum relative change of output voltage when the load current changes from zero to the maximum under the rated grid voltage (100-240Vac). It is usually expressed as a percentage or sometimes as an absolute change. The general requirement is within 5%

3. Several index forms of ripple voltage

(1) ripple coefficient y (%)

Under the rated load current, the ratio of the effective value Urms of the output ripple voltage to the output DC voltage uo, i.e. y = umrs / uo X100%.

(2) maximum ripple voltage

Under rated output voltage and load current, the absolute value of output voltage ripple (including noise) is usually expressed as peak value or effective value. Generally, 100 / 240VAC no-load and full load ripple shall be measured

⑶ ripple voltage suppression ratio

Under the specified ripple frequency (e.g. 50Hz), the ratio of ripple voltage UI ~ in input voltage to ripple voltage uo ~ in output voltage, i.e. ripple voltage suppression ratio = UI ~ / uo ~.

Electrical safety requirements

(1) safety requirements for power supply structure

① Space requirements

UL, CSA and VDE Safety specifications emphasize the distance requirements of surface and space between live parts and between live parts and non live metal parts. UL and CSA requirements: there shall be a distance of 0.1 inch between high-voltage conductors with inter pole voltage greater than or equal to 250VAC, and between high-voltage conductors and non charged metal parts (excluding conductors here), both between surfaces and in space; VDE requires 3mm creep or 2mm clearance between AC lines; IEC requirements: there is 3mm clearance between AC lines and 4mm clearance between AC lines and grounding conductors. In addition, VDE and IEC require at least 8mm space between the output and input of the power supply.

② Dielectric test method

High voltage: between input and output, input and ground and input AC. Generally, 3KV 60s is the standard, and the production line is 3KV 3S.

③ Leakage current measurement

The leakage current is the current flowing through the input side ground wire. In the switching power supply, it is mainly through the bypass capacitor of the squelch filter. UL and CSA require that the exposed uncharged metal parts should be connected with the earth. The leakage current measurement is by connecting a resistance of 1.5k Ω between these parts and the earth, and the leakage current should not be greater than 5 millima. VDE allows a resistance of 1.5k Ω to be connected in parallel with a 150npf capacitor, and 1.06 times the rated service voltage is applied. For data processing equipment, the leakage current should not be greater than 3.5ma, generally about 1mA.

④ Insulation resistance test

VDE requirements: there shall be a resistance of 7m Ω between the input and low-voltage output circuit, and a resistance of 2m Ω or 500V DC voltage shall be added between the accessible metal part and the input for 1min.

⑤ Printed circuit board

UL Listed 94v-2 material or better is required. Common plates include (FR-1, FR-4, CEM-1)

(2) safety requirements for power transformer structure

① Insulation of transformer

The copper wire used in the winding of the transformer shall be enamelled wire, and other metal parts shall be coated with porcelain, paint and other insulating materials. There shall be at least 4mm safety distance between primary stages, which is generally met by adding retaining wall or using three layers of insulated wire

② Dielectric strength of transformer

During the test, the insulation layer shall not be broken or flashed. Generally, high voltage 3750VAC shall prevail.

③ Insulation resistance of transformer

The insulation resistance between transformer windings shall be at least 10m Ω. Apply 500V DC voltage between winding and magnetic core, skeleton and shielding layer for 1min, and there shall be no breakdown and arcing.

④ Transformer humidity resistance

After the transformer is placed in a humid environment, the insulation resistance and dielectric strength test must be carried out immediately and meet the requirements. The humid environment is generally: the relative humidity is 92% (tolerance is 2%), the temperature is stable between 20 ℃ and 30 ℃, and the error is allowed to be 1%. The above experiment shall be carried out immediately after it is placed inside for at least 48h. At this time, the temperature of the transformer itself should not be 4 ℃ higher than the test before entering the humid environment.

⑤ VDE requirements for transformer temperature characteristics.

⑥ UL, CSA requirements on transformer temperature characteristics.

5 electromagnetic compatibility test

Electromagnetic compatibility refers to the ability of equipment or system to work normally in the common electromagnetic environment without unbearable electromagnetic interference to anything in the environment.

Electromagnetic interference wave generally has two transmission ways, which should be evaluated according to each way. One is to propagate to the power line in the frequency band with long wavelength and interfere with the transmission area, which is generally below 30MHz. The frequency with longer wavelength is less than one wavelength within the length range of the power line attached to the electronic equipment, and the amount of radiation to the space is also small. Therefore, the voltage on the power line can be mastered, and then the size of the interference can be fully estimated. This noise is called conducted noise.

When the frequency reaches more than 30MHz, the wavelength will become shorter. At this time, if only the noise source voltage generated in the power line is charged, it is inconsistent with the actual interference. Therefore, the method of directly measuring the magnitude of the interference wave * valence noise transmitted to space is adopted, which is called radiated noise. The methods of measuring the radiated noise include the direct measurement of the interference wave in the propagation space according to the electric field intensity and the measurement of the power leaked to the power line.

Electromagnetic compatibility test includes the following test contents:

① Magnetic field sensitivity

(immunity) undesired response of equipment, subsystem or system exposed to electromagnetic radiation. The smaller the sensitivity level, the higher the sensitivity and the worse the immunity. Including magnetic field test with fixed frequency and peak to peak value.

② Electrostatic discharge sensitivity

Objects that are in direct contact with each other or have different electrostatic potentials. The 300pf capacitor is charged to - 15000V and discharged through 500 Ω resistance. It can be out of tolerance, but it should be normal after playing. After the test, data transmission and storage shall not be lost.

③ Power transient sensitivity

Including peak signal sensitivity (0.5 μ s、10 μ S), voltage transient sensitivity (10% - 30%, 30s recovery), frequency transient sensitivity (5% - 10%, 30s recovery).

④ Radiation sensitivity

Measurement of radiated interference field causing equipment degradation. (14khz-1ghz, electric field intensity 1V / M).

⑤ Conduction sensitivity

The measurement of interference signals or voltages on power, control, or signal lines when they cause unwanted response or degradation of equipment performance. (30Hz-50kHz/3V，50kHz -400MHz/1V)。

⑥ Non working magnetic field interference

The packing box is 4.6m, and the magnetic flux density is less than 0.525 μ T； 0.9m，0.525 μ T。

⑦ Working state magnetic field interference

The AC flux density of upper, lower, left and right is less than 0.5mT.

⑧ Conducted interference

Interference propagating along a conductor. 10kHz-30MHz,60(48)dB μ V。

⑨ Radiation interference

Electromagnetic interference transmitted in the form of electromagnetic waves through space. 10khz-1000mhz, 30 shielded room 60 (54) μ V/m。

The latest power adapter, CEC, etc

For example, no-load power consumption shall not be greater than 0. 3W

As a new energy product, switching power supply is also the heart of electrical products. If the switching power supply does not work normally, it will cause the abnormal operation of the whole electrical appliance. Here are some basic parameters of switching power supply.

1 describe several index forms of input voltage affecting output voltage

(1) voltage stabilizing coefficient

① Absolute voltage stabilizing coefficient K of switching power supply (linear adjustment rate)

Indicates the ratio of the output DC voltage variation △ uo of the regulated power supply to the input grid voltage variation △ UI when the load is unchanged, i.e. k = △ uo / △ UI. The general requirements of the switching power supply are 3%

(2) grid adjustment rate

The grid adjustment rate of switching power supply indicates the relative change of output voltage of regulated power supply when the input grid voltage changes / - 10% from the rated value (90-264VAC), sometimes expressed as absolute value. Generally within 5%

2 several index forms of the influence of load on output voltage

(1) load regulation rate (also known as current regulation rate)

It refers to the maximum relative change of output voltage when the load current changes from zero to the maximum under the rated grid voltage (100-240Vac). It is usually expressed as a percentage or sometimes as an absolute change. The general requirement is within 5%

3. Several index forms of ripple voltage

(1) ripple coefficient y (%)

Under the rated load current, the ratio of the effective value Urms of the output ripple voltage to the output DC voltage uo, i.e. y = umrs / uo X100%.

(2) maximum ripple voltage

Under rated output voltage and load current, the absolute value of output voltage ripple (including noise) is usually expressed as peak value or effective value. Generally, 100 / 240VAC no-load and full load ripple shall be measured

⑶ ripple voltage suppression ratio

Under the specified ripple frequency (e.g. 50Hz), the ratio of ripple voltage UI ~ in input voltage to ripple voltage uo ~ in output voltage, that is, ripple voltage suppression ratio = UI ~ / uo ~.

Electrical safety requirements

(1) safety requirements for power supply structure

① Space requirements

UL, CSA and VDE Safety specifications emphasize the distance requirements of surface and space between live parts and between live parts and non live metal parts. UL and CSA requirements: there shall be a distance of 0.1 inch between high-voltage conductors with inter pole voltage greater than or equal to 250VAC, and between high-voltage conductors and non charged metal parts (excluding conductors here), both between surfaces and in space; VDE requires 3mm creep or 2mm clearance between AC lines; IEC requirements: there is 3mm clearance between AC lines and 4mm clearance between AC lines and grounding conductors. In addition, VDE and IEC require at least 8mm space between the output and input of the power supply.

② Dielectric test method

High voltage: between input and output, input and ground and input AC. Generally, 3KV 60s is the standard, and the production line is 3KV 3S.

③ Leakage current measurement

The leakage current is the current flowing through the input side ground wire. In the switching power supply, it is mainly through the bypass capacitor of the squelch filter. UL and CSA require that the exposed uncharged metal parts should be connected with the earth. The leakage current measurement is by connecting a resistance of 1.5k Ω between these parts and the earth, and the leakage current should not be greater than 5 millima. VDE allows a resistance of 1.5k Ω to be connected in parallel with a 150npf capacitor, and 1.06 times the rated service voltage is applied. For data processing equipment, the leakage current should not be greater than 3.5ma, generally about 1mA.

④ Insulation resistance test

VDE requirements: there shall be a resistance of 7m Ω between the input and low-voltage output circuit, and a resistance of 2m Ω or 500V DC voltage shall be added between the accessible metal part and the input for 1min.

⑤ Printed circuit board

UL Listed 94v-2 material or better is required. Common plates include (FR-1, FR-4, CEM-1)

(2) safety requirements for power transformer structure

① Insulation of transformer

The copper wire used in the winding of the transformer shall be enamelled wire, and other metal parts shall be coated with porcelain, paint and other insulating materials. There shall be at least 4mm safety distance between primary stages, which is generally met by adding retaining wall or using three layers of insulated wire

② Dielectric strength of transformer

During the test, the insulation layer shall not be broken or flashed. Generally, high voltage 3750VAC shall prevail.

③ Insulation resistance of transformer

The insulation resistance between transformer windings shall be at least 10m Ω. Apply 500V DC voltage between winding and magnetic core, skeleton and shielding layer for 1min, and there shall be no breakdown and arcing.

④ Transformer humidity resistance

After the transformer is placed in a humid environment, the insulation resistance and dielectric strength test must be carried out immediately and meet the requirements. The humid environment is generally: the relative humidity is 92% (tolerance is 2%), the temperature is stable between 20 ℃ and 30 ℃, and the error is allowed to be 1%. The above experiment shall be carried out immediately after it is placed inside for at least 48h. At this time, the temperature of the transformer itself should not be 4 ℃ higher than the test before entering the humid environment.

⑤ VDE requirements for transformer temperature characteristics.

⑥ UL, CSA requirements on transformer temperature characteristics.

5 electromagnetic compatibility test

Electromagnetic compatibility refers to the ability of equipment or system to work normally in the common electromagnetic environment without unbearable electromagnetic interference to anything in the environment.

Electromagnetic interference wave generally has two transmission ways, which should be evaluated according to each way. One is to propagate to the power line in the frequency band with long wavelength and interfere with the transmission area, which is generally below 30MHz. The frequency with longer wavelength is less than one wavelength within the length range of the power line attached to the electronic equipment, and the amount of radiation to the space is also small. Therefore, the voltage on the power line can be mastered, and then the size of the interference can be fully estimated. This noise is called conducted noise.

When the frequency reaches more than 30MHz, the wavelength will become shorter. At this time, if only the noise source voltage generated in the power line is charged, it is inconsistent with the actual interference. Therefore, the method of directly measuring the magnitude of the interference wave * valence noise transmitted to space is adopted, which is called radiated noise. The methods of measuring the radiated noise include the direct measurement of the interference wave in the propagation space according to the electric field intensity and the measurement of the power leaked to the power line.

Electromagnetic compatibility test includes the following test contents:

① Magnetic field sensitivity

(immunity) undesired response of equipment, subsystem or system exposed to electromagnetic radiation. The smaller the sensitivity level, the higher the sensitivity and the worse the immunity. Including magnetic field test with fixed frequency and peak to peak value.

② Electrostatic discharge sensitivity

Charge transfer caused by the proximity or direct contact of objects with different electrostatic potentials. The 300pf capacitor is charged to - 15000V and discharged through 500 Ω resistance. It can be out of tolerance, but it should be normal after playing. After the test, data transmission and storage shall not be lost.

③ Power transient sensitivity

Including peak signal sensitivity (0.5 μ s、10 μ S), voltage transient sensitivity (10% - 30%, 30s recovery), frequency transient sensitivity (5% - 10%, 30s recovery).

④ Radiation sensitivity

Measurement of radiated interference field causing equipment degradation. (