FAQ of LED drive power supply

1. LED driving circuit directly affects LED life

The LED driver we mentioned includes digital driver and analog driver. Digital driver refers to digital circuit driver, including digital dimming control, RGB full-color change, etc. Analogue drive refers to analog circuit drive, including AC constant current switching power supply and DC constant current control circuit. The drive circuit is composed of electronic components, including semiconductor components, resistors, capacitors, inductors, etc. These components have a service life. Failure of any one device will cause the failure of the entire circuit or some functions. The life span of LED is 50000 to 100000 hours, which is calculated as 50000 hours, and the life span of LED is nearly 6 years. The life span of switching power supply is very difficult to reach 6 years. The warranty period of switching power supply sold on the market is usually 2-3 years. The power supply with a warranty of 6 years is military grade, and the price is 4-6 times of the normal power supply. The normal lamp factory is very difficult to bear. So most of the problems of LED lamps are driver circuit problems.

2. LED drive power cooling problem

LED is a cold light source, the operating junction temperature cannot exceed the limit value, and a certain margin should be left when painting. The description of the whole lamp should consider many problems, such as beautiful appearance, convenient installation, light distribution, heat dissipation, etc., and seek a balance point among many factors, so that all lamps are the best. The development of LED lamps is not long, and there is not much experience to learn. Many descriptions are constantly improved. Some LED lamp manufacturers use outsourcing or outsourcing power supply. The lamp delineator does not know much about power supply. The heat dissipation space for LED is large, and the heat dissipation space for power supply is small. It is usually to find a suitable power supply after describing the lamps, which will bring certain difficulties to the matching of power supply. It is often encountered that due to the small internal space of the lamp or the high internal temperature, and the low cost control, it is unable to match the appropriate power supply. Some LED lamp manufacturers have the ability to develop power supply. They can deal with the above problems by evaluating the lamps in the early stage of the initial description, and the description of power supply is carried out simultaneously. In the description, we should sum up and think about the heat dissipation of LED and power supply, and control the temperature rise of lamps, so as to describe better lamps.

3. Difficulties in LED driver power description

A. Power description. Despite the high luminous efficiency of LED, there is still 80-85% heat loss, resulting in a 20-30 degree temperature rise inside the lamp. If the room temperature is 25 degrees, there will be 45-55 degrees inside the lamp. The power supply works in a high temperature environment for a long time, and to ensure its service life, the power margin must be increased, usually to 1.5-2 times the margin.

B. Component selection. When the internal temperature of the lamp is 45-55 degrees, and the internal temperature rise of the power supply is about 20 degrees, the temperature near the element should reach 65-75 degrees. Some components will drift under high temperature conditions, and some will shorten their service life. Therefore, equipment should be selected that can be used at high temperature for a long time, with special attention to electrolytic capacitors and wires.

C. Electrical function description. The parameter description of switching power supply aiming at LED is mainly constant current parameter. The size of current determines the brightness of LED. If the batch current error is large, the brightness of the whole batch of lamps is uneven. And the change of temperature can also cause the output current of the power supply to shift.

E. Certification difficulties. At present, there is no specification for LED lamps in China, and the relevant parts of the country are discussing and formulating. The certification of lamps sold in China is based on the specifications of lighting lamps, while the certification of lamps sold in China is based on CE or UL certification, and some are based on the specifications of LED lamps abroad. Therefore, it is difficult to meet the above specifications in the description of switching power supply. We can only meet different requirements with different authentication.

4. LED driving power application parameters.

The selection of outsourced drive power mainly depends on the voltage scale of constant current and constant current. The constant current value is selected as the lower standard current of LED. The selection of voltage scale should be moderate, and try not to select a larger scale to prevent the waste of power.

Protection method of LED driving power supply

1. Fuse (tube) is used in the protection LED drive power supply

Because the fuse is disposable, slow in response, poor in effect and troublesome in use, it is not suitable for use in finished LED lamps, because LED lamps are mainly used in urban brilliance projects and lighting projects. It requires the LED protection circuit to be very strict: when the normal use current is exceeded, the protection can be started immediately, so that the power supply path of the LED can be disconnected, so that both the LED and the power supply can be protected, and the power supply can be automatically restored after the whole lamp is normal, without affecting the LED operation. The circuit should not be too complex, the volume should not be too large, and the cost should be lower. So it is very difficult to use fuse.

2. LED driver uses transient voltage suppression diode

Transient voltage suppression diode is a kind of high-efficient protection device in the form of diode. When its two poles are impacted by reverse transient high energy, it can immediately reduce the high resistance between its two poles to low resistance at the speed of 10 to the 12th power of a very short time, absorb the surge power of several kilowatts, and clamp the voltage between the two poles at a predetermined voltage value, effectively protecting the precision components in the electronic circuit. Transient voltage suppression diode has the advantages of fast response time, large transient power, low leakage current, good consistency of breakdown voltage deviation, easy control of clamp voltage, no damage limit, small size, etc.

However, it is difficult to find TVS devices that meet the required voltage value in practical use. The damage of LED light bead is mainly caused by excessive current and overheating inside the chip. TVS can only detect overvoltage but not overcurrent. It is difficult to master the proper voltage protection point, and this device cannot be produced and is difficult to use in practice.

3. LED drive power selection self-recovery fuse

Self-recovery fuse, also known as polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. When the normal working current passes (or the element is at normal ambient temperature), the PTC self-recovery fuse is in low resistance state; When there is abnormal overcurrent in the circuit (or the ambient temperature rises), the heat generated by the high current (or the ambient temperature rises) causes the polymer to expand rapidly, which also cuts off the conductive path formed by conductive particles, and the PTC self-recovery fuse is in a high resistance state; The heat of the self-recovery fuse is very small under normal working conditions, and its high heat resistance value is very high under abnormal working conditions, which limits the current passing through it, thus protecting the LED driving power supply.

How to solve the damage problem of LED drive power supply

In order to solve the problems of high failure rate and difficult maintenance of LED driving power supply, we try to use low-voltage DC power supply mode in LED road lighting through the analysis of LED luminous principle and power supply demand, combined with the current practical application. DC power supply can not only reduce the failure rate of LED drive power supply, but also reduce the safety risk of road lighting, and provide convenience for charging electric vehicles in the future.

With the continuous development of light-emitting diode (LED) technology, LED lighting has gradually expanded from indoor to outdoor. The reason for the slow promotion of LED in the field of road lighting is the high power of road lighting and the bad operating environment. After a period of tracking and detection of high-power LED street lamps, some LED lamps have successively failed. Through the analysis of the fault, we found that the proportion of LED driver power damage was up to 90%. Although the theoretical service life of LED street lamp is up to 50000 hours (13.7 years), its driving circuit has a short service life of about 12000 hours (3 years). The driving power supply becomes the short board that restricts the service life of LED street lamps. At the same time, due to the lack of uniform standards, the LED driver power supply needs to match the LED particles, and the output interface of the driver power supply produced by various suppliers is not uniform, and the quality is uneven, which brings inconvenience to the maintenance of LED street lamps, and the cost of replacing the driver power supply is high.

LED drive power has been included in the category of national 3C compulsory certification. Power supply has become an important factor affecting the promotion and application of LED lamps. Only by solving the problem of LED power supply can the application of LED lamps in road lighting be opened.