An LED emits light by applying voltage to its PN junction to form an energy level transition that produces photons.
The LED device cannot be directly connected to 220V ac, but needs to be powered by a low voltage of 2-3v. In other words, complex conversion circuit (drive circuit) should be designed according to different USES and supply voltage.
LED drive circuit should have the characteristics of high power conversion efficiency, high reliability, high power factor, low cost and small volume.
LED drive circuit power supply type
Drive circuits can be divided into two types according to the supply voltage: DC supply low voltage (0.8-1.65v) batteries (such as button batteries), and the drive circuit should adopt DC/DC booster converter.
For other DC power supply greater than 5V, the driving circuit shall adopt DC/DC buck converter;
The power supply which is directly supplied by AC power is usually required to undergo AC/DC/DC transformation before being available.
Main technology of LED lighting drive circuit
LED lighting circuits are also divided into two categories by drive mode.
The output current of constant current drive is unchanged, and the output voltage varies with load resistance.
The output voltage of constant pressure drive is unchanged, and the output current changes with the increase and decrease of load resistance.
Constant current drive is an ideal method, and the actual driving circuit has constant pressure and constant current function.
LED lighting drive circuit can be divided into two types, namely device buck and PWM switching power supply.
The buck of the device includes resistance capacity, resistance and transformer.
PWM switching power supply refers to the driving mode which adjusts the width of the conducting pulse of the main circuit switching device to keep the output voltage or current stable.
Changing the duty cycle can change the average drive current of the LED, thus changing its luminous intensity.
LED lighting drive circuit typical chip
When the LED lighting circuit needs to adjust the brightness, the control mode mainly includes linear adjustment of LED current (analog dimming) and PWM setting duty ratio and working cycle (digital dimming).
In the face of hundreds of LED drive chips from domestic and foreign electronics companies, we suggest: first, we should try to choose products of big brands; second, we should consider quality and cost comprehensively according to our needs.
Here is a list of typical drive chip models commonly used.
(1) foreign products
Is American letter -MAX168XX series.
MAX16818 working voltage range of 4.75-28v, output current of 30A, wide range of brightness adjustment can be achieved through PWM signal.
MAX16819/MAX16820 input voltage range 4.5-28v, drive current 3A.
MAX16832A/MAX16832C input voltage range is 6.5-65v, maximum output current 1A.
MAX16802A/B for low voltage (10.8-24v) lighting and display drives.
The U.S. ti-lm340x series.
The input voltage range of LM3401 is 4.5-35v, and the output current reaches 3A.
The output current of LM3402 is 1A.
LM3405A can output 1A constant current and drive 3W or 5W leds.
The LM3405A can drive general lighting systems with 12V ac and 12V dc.
British getco -ZXLD1350.
Input voltage range 7-30v, maximum output current 350mA, maximum output power 8W.
Shine Japan Toshiba -MP4021A.
MP4021A built-in PFC (power factor correction), input voltage range 90-264v, output voltage range 36-42v, output current 420mA.
(2) domestic products.
Maison technology -MT7930.
This is an isolated driving IC with an ac input voltage range of 85-265v, high-precision constant current output, and a drive capacity of 50W. The output current and output power can be adjusted.
(3) Taiwan guangpeng technology -AMC7150.
AMC7150 can be used for automobile and general lighting LED drive, input working voltage range of 4-40v, drive current up to 1.5a, output power 24W.
In the case of meeting the technical requirements, quality and price are the main factors to be considered in the selection of product IC.
Toshiba, Texas instruments, half of the IC price more expensive, but reliable quality.
In addition, enzhipu, yingfeiling, dianjing technology and other companies are good products.
Domestic chip has obvious advantage in cost, can choose according to need.
With the increasing power of LED light source, chipmakers are also competing to develop more integrated and intelligent IC drive solutions and keep reducing costs.