If the power supply is not good, we will have to work overtime.

Anyone who makes products cannot do without a power supply. If there is a problem with the product, the first thing to check is whether the power supply is normal. What I want to share with you today is what factors need to be considered to make a good power supply.

one. Several index forms describing the influence of input voltage on output voltage

1. Stability coefficient

A. Voltage stabilization coefficient: Indicates the ratio of the output DC change amount △U0 of the regulated power supply to the change amount △Ui of the input power grid when the load remains unchanged. That is: K=△U0/△Ui.

B． Relative voltage stabilization coefficient: indicates the ratio of the relative change amount ΔUo of the regulator output DC voltage ΔUo to the relative change amount Ui of the output power grid Ui when the load remains unchanged. That is: S=△Uo/Uo /△Ui/Ui.

2. Grid adjustment rate

It represents the relative change in the output voltage of the regulated power supply when the input grid voltage changes ±10% from the rated value. Sometimes it is also expressed in .

3. Voltage stability

The load current remains at any value within the rated range, and the relative change in the output voltage caused by the input voltage changing within the specified range (ΔUo/Uo percentage) is called the voltage stability of the voltage regulator.

two. Several index forms of the impact of load on output voltage

1. Load regulation (also called current regulation)

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

2. Output resistance (also called equivalent internal resistance or internal resistance)

Under the rated grid voltage, due to the change in load current △IL causing the output voltage to change △Uo, the output resistance is Ro=|△Uo/△IL| ohms.

three. Several index forms of ripple voltage

1. ripple voltage

Under the rated output voltage and load current, the size of the output voltage ripple (including noise) is usually expressed in peak-to-peak or effective value.

2. Ripple coefficient Y (%)

Under the rated load current, the ratio of the effective value of the output ripple voltage Urms to the output DC voltage Uo, that is, y=Umrs/Uo x100%

3． Ripple voltage rejection ratio

Under the specified ripple frequency (for example, 50Hz), the ratio of the ripple voltage Ui~ in the output voltage to the ripple voltage Uo~ in the output voltage, that is: ripple voltage suppression ratio = Ui~/Uo~.

Let me make a statement here: noise is different from ripple. Ripple is a component that appears between the output terminals and is synchronized with the input frequency and switching frequency. It is represented by a peak-to-peak value and is generally less than 0.5% of the output voltage; noise appears between the output terminals. A high-frequency component other than ripple, also expressed as a peak-to-peak value, generally around 1% of the output voltage. Ripple noise is a combination of the two, expressed as a peak-to-peak value, which is generally less than 2% of the output voltage.

Four. electric shock

Inrush current refers to the instantaneous current that passes before the input current reaches a stable state when the input voltage is turned on or off at specified intervals.

Generally 20A-30A.

five. Overcurrent protection

Overcurrent protection is a power supply load protection function to avoid damage to the power supply and load caused by overload output current including short circuit on the output terminals.

The given value of overcurrent is generally 110% - 130% of the rated current.

six. Overvoltage protection

Overvoltage protection is a function that protects the load from excessive voltage between terminals.

The general rule is 130%-150% of the output voltage.

seven. Output undervoltage protection

When the output voltage is below the standard value, it detects the output voltage drop or stops the power supply and sends an alarm signal to protect the load and prevent misoperation.

Mostly about 80%-30% of the output voltage.

eight. Overheating protection

When an abnormality occurs inside the power supply or the temperature of the power supply exceeds the standard due to improper use, it stops the power supply and sends an alarm signal.

Nine. Temperature drift and temperature coefficient

Temperature drift: Changes in ambient temperature affect changes in the parameters of components, thereby causing changes in the output voltage of the voltage regulator. Commonly used temperature coefficients represent the size of temperature drift.

Temperature coefficient: A change in temperature of 1 degree Celsius causes a change in the output voltage value △UoT, the unit is V/℃ or millivolts per degree Celsius.

Relative temperature coefficient: A temperature change of 1 degree Celsius causes a relative change in the output voltage △UoT/Uo, the unit is V/℃.

ten. drift

When the input voltage, load current and ambient temperature of the voltage regulator remain constant, the stability of the component parameters will also cause changes in the output voltage. Slow changes are called drift, fast changes are called noise, and the difference between the two is called fluctuations.

There are two ways to express drift:

The change in output voltage value △Uot within the specified time.

The relative change of the output voltage within the specified time ΔUot/Uo.

The time period for examining drift can be 1 minute, 10 minutes, 1 hour, 8 hours, or longer. Only in voltage regulators with higher precision, there are two indicators: temperature coefficient and temperature drift.

eleven. Response time

Response time refers to the adjustment time for the output voltage of the voltage regulator to reach a new stable value when the load current changes suddenly.

In a DC voltage regulator, the output voltage waveform at a rectangular wave load current is used to represent this characteristic, which is called the over characteristic.

twelve. distortion

Distortion This is specific to AC regulators. It means that the output waveform is not a positive waveform and causes waveform distortion, which is called distortion.

Thirteen. noise

According to the audible frequency regulation of 30Hz-18kHZ, this is not a problem for the switching frequency of the switching power supply, but the power supply with a fan must be stipulated as needed.

fourteen. input noise

In order to maintain the normal operation of the switching power supply, the input noise index must be determined based on the rated input conditions and the pulse voltage (0-peak) that is outside the allowed input and superimposed on the industrial frequency.

Generally, the applied pulse width is 100-800us, and the applied voltage is 1000V.

fifteen. surge

This is to add a surge voltage to the input voltage a specified number of times at intervals of more than 1 minute to avoid abnormal phenomena such as insulation damage, flashover, and arcing.

The specified value for communication equipment, etc. is thousands of volts, generally 1200V.

sixteen. static noise

Refers to a repetitive pulse-like static electricity that can maintain normal working conditions in the full output circuit when applied to any part of the power supply frame under rated input conditions.

Generally guaranteed to be within 5-10KV.

Seventeen. stability

Under the allowed use conditions, the relative change of output voltage is △Uo/Uo.

eighteen. Electrical safety requirements (GB 4943-90)

1. Safety requirements for power supply structures

1) Space requirements

UL, CSA, VD degrees.

5) VDE requirements on transformer temperature characteristics

6) UL and CSA requirements on transformer temperature characteristics.

Note:

①IEC:

International Electrotechnical Commission

②VDE: Verbandes

③Deutcher ElectrotechnICer

④UL: Underwriters’ Laboratories

⑤CSA: CANadian Standards Association

⑥FCC:

Federal Communications Commission

nineteen. Radio disturbance (tested in accordance with GB 9254-1998)

1. Power terminal disturbance voltage limit

2. Radiation disturbance limits

twenty. Electromagnetic compatibility test

Electromagnetic compatibility test (electromagnetIC compatiblity EMC)

Electromagnetic compatibility refers to the ability of equipment or systems to work normally in a common electromagnetic environment without causing intolerable electromagnetic interference to anything in the environment.

Electromagnetic interference waves generally have two propagation paths, and each path must be evaluated. One is to propagate to the power line in a frequency band with a long wavelength, causing interference to the emission area, generally below 30MHz. This long-wavelength frequency is less than 1 wavelength within the length of the power cord attached to electronic equipment, and the amount of radiation it radiates into space is very small. This allows the voltage occurring on the power cord to be understood and fully evaluated. The size of the interference, this kind of noise is called conducted noise.

When the frequency reaches above 30MHz, the wavelength also becomes shorter. At this time, if we only evaluate the noise source voltage occurring on the power line, it will not be consistent with the actual interference. Therefore, a method was adopted to evaluate the size of the noise by directly measuring the interference waves propagating into space. This noise is called radiated noise. Methods for measuring radiated noise include the above-mentioned method of directly measuring interference waves in the propagation space according to the electric field strength and the method of measuring the power leaked to the power line.

Electromagnetic compatibility testing includes the following tests:

① Magnetic field sensitivity: (Immunity) The degree of undesirable response of equipment, subsystems or systems exposed to electromagnetic radiation. The smaller the sensitivity level, the higher the sensitivity and the worse the immunity. Fixed frequency, peak-to-peak magnetic field

② Electrostatic discharge sensitivity: charge transfer caused by objects with different electrostatic potentials approaching each other or in direct contact. The 300PF capacitor is charged to -15000V and discharged through the 500 ohm resistor. It can be out of tolerance, but it should be normal after discharge. Data is transferred and stored and cannot be lost

③ Power supply transient sensitivity: including spike signal sensitivity (0.5us 10us 2 times), voltage transient sensitivity (10%-30%, 30S recovery), frequency transient sensitivity (5%-10%, 30S recovery) ).

④ Radiation sensitivity: A measure of the radiated interference field that causes equipment degradation. (14K-1GHz, electric field strength is 1V/M)

⑤ Conducted sensitivity: A measure of interfering signals or voltages on power, control, or signal lines that cause undesirable responses or degrade performance of the equipment. (30Hz-50KHZ 3V, 50K-400M 1V)

⑥ Non-working magnetic field interference: The magnetic flux density of the 4.6m packaging box is less than 0.525uT, and the 0.9m 0.525Ut.

⑦ Magnetic field interference in working state: upper, lower, left and right AC magnetic flux density is less than 0.5mT.

⑧ Conducted interference: interference propagating along conductors. 10KHz-30MHz 60(48)dBuV.

⑨ Radiation interference: electromagnetic interference that propagates through space in the form of electromagnetic waves. 10KHz-1000MHz 30 shielded room 60 (54) uV/m.

twenty one. environmental experiment

Environmental testing is the process of exposing products or materials to natural or artificial environments to evaluate their performance under storage, transportation and use conditions that may actually be encountered.

Including low temperature, high temperature, constant humidity and heat, alternating humidity and heat, collision (impact and collision), vibration, constant acceleration, storage, mold growth, corrosive atmosphere (such as salt spray), sand and dust, air pressure (high or low pressure), temperature changes , flammability, sealing, water, radiation (solar or nuclear), soldering, terminal strength, noise (micro-printing 65DB), etc.