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Detailed Explanation of Reliability Testing Indicators and Specifications for LED Power Supply

2019/10/11

1. Several Indicators of Input Voltage Affecting Output Voltage

(1) voltage stabilizing coefficient

Absolute Pressure Regulating Coefficient K

It indicates the ratio of output DC voltage variation △ uo of regulated power supply to input grid voltage variation △ UI when the load is constant, i.e. k = △ uo / △ UI.

(2) Relative voltage stabilization coefficient S

When the load is constant, the ratio of the output DC voltage Uo/Uo of the regulator to the input grid voltage Ui/Ui is S= Uo/Uo/Delta Ui/Ui.

(2) Power grid adjustment rate

Represents the relative variation of the output voltage of a regulated power supply when the input grid voltage changes from +/-10% of the rated value, sometimes expressed in absolute terms.

(3) Voltage stability

Load current is maintained at any value within the rated range. The relative change of output voltage caused by the change of input voltage in the specified range Uo/Uo (percentage) is called voltage stability of voltage regulator.

2. Several Indicators of the Impact of Load on Output Voltage

(1) Load adjustment rate (also known as current adjustment rate)

Under the rated grid voltage, when the load current changes from zero to the maximum, the maximum relative change of the output voltage is usually expressed as a percentage, sometimes as an absolute change.

(2) Output Resistance (also known as Equivalent Internal Resistance or Internal Resistance)

Under rated grid voltage, the output resistance is Ro= | Uo/ IL _ Omega due to the change of load current IL, which causes the change of output voltage Uo.

3. Several Index Forms of Ripple Voltage

(1) 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 valid value.

(2) Ripple coefficient Y(%)

Under rated load current, the effective value of output ripple voltage is the ratio of Urms to output DC voltage Uo, that is Y = Umrs / Uo x 100%.

_Ripple Voltage Suppression Ratio

Under the specified ripple frequency (such as 50HZ), the ratio of the ripple voltage Ui~in the input voltage to the ripple voltage Uo~in the output voltage is: the ripple voltage rejection ratio = Ui~/Uo~.

4. Electrical Safety Requirements

(1) Safety requirements of power supply structure

space requirements

UL, CSA and VDE Safety specifications emphasize the requirements of surface and space distance between live parts and between live parts and non-live metal parts. UL, CSA requirements: high voltage conductors with voltage greater than or equal to 250 VAC, and high voltage conductors and non-live metal parts (excluding conductors), whether in surface space or space, should be 0.1 inches; VDE requires a 3 mm creep or 2 mm net space gap between AC lines; IEC requirements: 3 mm net space gap between AC lines and between AC lines and grounding Clear space gap of 4mm between conductors. In addition, VDE and IEC require at least 8 mm spacing between the output and input of the power supply.

(2) Test method of dielectric experiment

High voltage: between input and output, input and ground, and input AC.

(3) Leakage current measurement

Leakage current is the current flowing through the input side ground wire. In the switching power supply, leakage current is mainly through the bypass capacitor of the noise filter. Both UL and CSA require that the exposed non-charged metal parts should be connected with the earth. Leakage current is measured by connecting these parts to the earth with a resistance of 1.5k, and the leakage current should be less than 5mA. VDE permits parallel connection of 1.5k resistance with 150nPF capacitor and application of 1.06 times rated service voltage. For data processing equipment, leakage current should be no more than 3.5mA, generally about 1mA.

Insulation resistance test

VDE requirements: there should be 7M resistance between the input and low voltage output circuits, and 2M resistance or 500V DC voltage between the metal parts that can be contacted and the input should last for 1 minute.

_Printed Circuit Board

Require the use of UL certified 94V-2 materials or better materials.

(2) Safety requirements for power transformer structure

Transformer insulation

Copper wires used in transformer windings shall be enameled wires, and other metal parts shall be coated with insulating materials such as porcelain and lacquer.

(2) Dielectric strength of transformer

The phenomenon of insulating layer rupture and flying arc should not occur in the experiment.

(3) Insulation Resistance of Transformer

The insulation resistance between transformer windings is at least 10M. 500 V DC voltage is applied between windings and magnetic core, skeleton and shielding layer for 1 min. No breakdown or arc phenomenon should occur.

(4) Humidity Resistance of Transformer

Transformers must be placed in a humid environment immediately after the insulation resistance and dielectric strength experiments, and meet the requirements. In humid environment, the relative humidity is 92% (tolerance is 2%) and the temperature is stable between 20 and 30 ~C. The error is allowed to be 1%.

5. EMC test

Electromagnetic compatibility (EMC) refers to the ability of a device or system to work normally in a common electromagnetic environment and not to cause unbearable electromagnetic interference to anything in that environment.

Generally, there are two ways of electromagnetic interference wave propagation, which should be evaluated according to different ways. One is to propagate to the power line in a longer wavelength band and to interfere with the transmitting area, usually below 30MHz. The longer frequency of this kind of wavelength is less than one wavelength in the length range of the power line attached to the electronic equipment, and the amount of radiation to space is very small. Thus, the voltage occurring on the power line of the LED can be grasped, and the magnitude of interference can be fully evaluated. This kind of noise is called conductive noise.

When the frequency reaches above 30MHz, the wavelength will also be shortened. At this time, if only the noise source voltage occurring in the power line is evaluated, it is inconsistent with the actual interference. Therefore, the method of evaluating the noise size by directly measuring the interference wave propagating into space is adopted, which is called radiated noise. The methods of measuring radiated noise include direct measurement of interference wave in propagation space according to electric field intensity and determination of power leakage to power line.

The EMC test includes the following contents:

(1) Magnetic field sensitivity

(immunity) the degree of unwanted response of equipment, subsystems or systems exposed to electromagnetic radiation. The smaller the sensitivity level, the higher the sensitivity, the worse the immunity. It includes magnetic field measurement with fixed frequency and peak value.

(2) Electrostatic discharge sensitivity

Charge transfer caused by close or direct contact between objects with different electrostatic potentials. The 300PF capacitor is charged to - 15000V and discharged through 500_resistance. It can be over-tolerant, but it should be normal after release. After testing, data transfer and storage can not be lost.

(3) Transient sensitivity of LED power supply

Including peak signal sensitivity (0.5, 10, 2 times), voltage transient sensitivity (10% - 30%, 30S recovery), frequency transient sensitivity (5% - 10%, 30S recovery).

Radiation sensitivity

The measurement of radiation interference field causing equipment degradation. (14kHz-1GHz, electric field intensity 1V/M).

Conduction sensitivity

The measurement of interference signals or voltages on power supply, control or signal lines when an unwanted response of the device is caused or its performance degraded. (30Hz-50kHz/3V, 50kHz-400MHz/1V).

Non-working magnetic field interference

Packing box 4.6m, magnetic flux density less than 0.525 UT; 0.9m, 0.525 UT.

Magnetic field interference in working state

Upper, lower, left and right AC flux density is less than 0.5mT.

_Conductive interference propagates along conductors. 10 kHz-30 MHz, 60 (48) dB uV.

Radiation interference: electromagnetic interference propagating in the form of electromagnetic waveform through space. 10 kHz-1000MHz, 30 shielding chamber 60(54)uV/m.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.