LED has become the standard solution for movie lighting and camera flash in mobile phones. For higher quality and higher resolution requirements, brighter flash LED solutions are required. The challenge is how to squeeze the best luminous flux from the battery by achieving the highest efficiency solution. In this way, the operation of absorbing large current from the battery requires many power-saving operating characteristics and a robust system design. This article will introduce a system-level flash LED driver design and some features that can ensure the safe operation and integration of the system.
Efficient camera flash LED driver
High-resolution cameras require a high-brightness flash to complete photography in the lowest light environment. The customer requested a flash solution as a standard feature of the mobile phone. Mobile phones with flash installed have become an attractive selling point. This feature requires high luminous flux, which challenges the design of efficient LED driver systems.
system design
The high forward voltage and current of the flash LED in the mobile phone and the given battery voltage make the boost converter the best solution. When driving large currents, inductance-based boost converters exhibit satisfactory efficiency. LEDs must be driven by current, because the forward voltage not only changes with temperature, but also has its own differences. This change in forward voltage stems from its production process, and its variation range is ± 20%, see Figure 1.
Figure 1 Flash LED VF / IF diagram
It is a simple method to connect the flash LED in series with a current sense resistor and then drive it through a boost converter. Figure 1 describes this method.
Figure 2 Simple LED driving method using external current sense resistor
The output voltage of the boost regulator is controlled to match the set LED current detected by an external resistor. Unfortunately, doing so will deviate from the goal of squeezing the highest luminous flux out of the limited power provided by the battery. The external current sense resistor has high power consumption and its size is controlled. The purpose is to provide a usable margin voltage in a low current state, thereby providing a drive for continuous movie lighting. On the other hand, if the current increases, the voltage drop of the current detection resistor will increase, bringing a lot of power consumption. In addition, high-precision resistors with ideal power dissipation ratings are more expensive and increase the size of the solution, requiring one resistor per LED channel.
Therefore, a better solution is an active current sink or current source integrated in the LED driver, as shown in Figure 3. We can use a method to reduce the voltage drop and the resulting power consumption to adjust the internal current sense resistor, the specific adjustment depends on the size of the LED current. If the LED current is low, the voltage drop can be kept high enough to obtain an accurate detection signal.
Figure 3 Improved LED driving scheme using adaptive current sink and detection
LED flag screen totem on light poles or Outdoor led screen kiosk, can save installation cost and time by pulling down and updating the printing advertising for light box. you can also unified management of intelligent management system. advertising can be really controlled,The Outdoor flat screen Is expected to become a large-scale media after as new carrier of advertising.
Small body, big world, It is not only small pixel pitch for led display, but a small era of led screen!
The flag LED display kiosk on each road poles, not only can realize the comprehensive utilization of road poles, making the road no longer monotonous, but also can play content according to different festivals and beauty the city. At the same time, it will also provide the public with weather changes, environmental pollution and road access. bring more convenience to the public.
Priva provides professional intelligent Led light pole screen solutions and professional commercial LED display technology With a wealth of LED project engineering experience, Priva Led will meet customer`s varity needs.
Integrated design, easy to use
Operate controller inside, Optional of installation on back column and side of pole, Easy to transport & install.
Intelligent management and Large scale cluster control and management. easy and convenient
Managing multiple displays via cable, 3G, 4G, WAN and LAN; Could manage by mobile phone with APP. 1-1 and 1-N management One click to release, timing, updating AD.
Outdoor Led Flag Screen Totem,Outdoor Led Flag Screen,Outdoor Flag Screen,Slim Outdoor Led Poster
Shenzhen Priva Tech Co., Ltd. , https://www.privaled.com