Current mainstream solutions for mobile phone flash

Mobile phones can be considered one of the fastest developing electronic products in recent years, with rapid development in CPU, GPU, screen size, storage space, camera modules, etc. Mobile flash, as a device that effectively improves the photo taking effect of mobile cameras in dark environments, is also increasingly being valued. There are many solutions for mobile phone flash on the market, and how to choose the appropriate flash device and solution depends on the performance of the camera module and the positioning of the mobile phone product. Let's take a look at the mainstream flash solutions in the current market:

1) Ultra low end false flashing

This solution mainly uses large-sized packages such as 2835 or 3014, which are currently widely used for backlighting. The driving current is relatively low, usually between 150mA and 300mA. This solution does not require a separate driver IC, and can be directly driven from the battery using the platform's current source or using a simple transistor to build a path. This solution is the lowest cost solution.

2) Midrange 8M pixels, low current drive

This solution is mostly used on 8M pixel phones, and 8M cameras have gradually become the mainstream configuration of mobile phones. The 2016 LED with a separate lens is the most commonly used solution. The performance of LED is generally around 200lm @ 1A. The driving current is between 500 and 600mA, and a relatively inexpensive Charge Pump can be used for driving.

3) High end 8M and above pixels, high current drive, high brightness requirements

Unlike the second type of scheme above, the 2016 LED performance requirement is above 250lm @ 1A, with a driving current of around 1A. In order to achieve high electrical efficiency, DC/DC drives are mostly used. These products also have higher requirements for the design and processing of lenses.

4) Above 10 million pixels, high brightness dual light scheme

The biggest advantage of using the same color temperature dual lamp scheme is that the appearance looks cooler and the brightness is higher. The same current distribution of 1A is applied to two LEDs, resulting in a lower current density for a single LED, a smaller increase in junction temperature, an improvement in luminous efficiency, and higher illumination. Cameras above 10 million pixels use a 1.1um Pixel size, which has poor sensitivity. All higher brightness LEDs are the most direct and effective way to improve the signal-to-noise ratio of photos under low illumination.

5) High brightness module solution above 10 million pixels

Compared to the single lamp and lens scheme, the module scheme has the advantages of high performance and stability, no assembly accuracy issues, and high relative cost, so it is only used for some high-end models.

6) Dual lamp adjustable color temperature module scheme

Package two LEDs with different color temperatures in a module, and mix white light with different color temperatures by adjusting the current passing through each LED. This solution must build a closed-loop system with the white balance of the mobile camera. Additional software workload is required, and the technical difficulty is high. If the software does not handle it properly, it will result in counterproductive photo color effects.

The main issues faced by customers in the design of mobile phone flash

Among all the above options, options 2 and 3 are currently the most mainstream options. As an LED supplier, we need to understand what problems customers have when using them, and these problems are what we need to help customers solve together.

How to determine the driving current of an LED? The driving current of LED determines the illuminance, and the higher the current, the higher the illuminance. The flash ultimately serves the camera's photography function, so how much current the LED requires and how much illumination it provides depends on the sensitivity of the camera we choose. Then, based on the SNR and color saturation curves of the photos taken, the minimum illumination requirement of this camera module is defined, and the driving current value of the LED is obtained.

In terms of thermal design optimization, in the confined space inside the mobile phone, high current drive can easily raise the LED junction temperature to above 100 degrees. So we need to optimize the placement of LED devices and stay away from various analog devices to avoid affecting their operation. Simultaneously optimize the PCB layout to fully utilize the heat dissipation effect of the PCB copper layer. Crystal energy optoelectronics can be combined with thermal simulation and actual testing of LED junction temperature to improve the optimization of thermal design.

Additionally, a special point to note is that the lens processing design requirements for LED flash lamps are also very high. The design is good, and the processing technology must also meet the standards, otherwise it cannot be achieved. LatticePower can provide customers with a complete set of LED+Lens solutions, eliminating the need for customers to separately process and retest lenses at a lens factory, and shortening the project development cycle. The customer only needs to provide a project schedule, and LatticePower will provide LED+lens and optical test reports to the customer according to the schedule.

The Development Trend of Mobile Phone Flash

There is a serious homogenization phenomenon in current mobile phone design, and the appearance design of each phone is very similar. Various mobile phone manufacturers are actively seeking differentiated design, and more and more mobile phone brands are focusing on differentiated design in mobile phone imaging systems. Of course, flash will be an essential part of it.

According to the design requirements of mobile phone manufacturers and the development statistics of LED technology, the future development trend of flash lights will be "high light efficiency", "high CRI", "modularization", and "personalization". Due to the limitation of the maximum output current of the battery, the driving current of the flash will not continue to increase and will remain at a maximum level of 1A. Therefore, it is required that LEDs have higher luminous efficiency under the same current.

The module solution is a very good solution for solving the large difference in structural assembly work and the inability to ensure optical performance. More and more mobile phone manufacturers are accepting modular design.

The front camera fill light has a great trend of popularity, as it can meet people's selfie needs under low illumination conditions. This application requires that the color reproduction of the photos be good enough, resulting in the requirement of high CRI.

Accompanied by quality and trend, practicing the "Chinese Dream" of LED mobile phone flash

During this period of highly homogeneous mobile phone products, major brand manufacturers are committed to finding ways to differentiate. Almost all mobile phone design manufacturers have put more emphasis on imaging systems, and more and more mobile phone brand manufacturers hope to have their own unique flash design solution, which can improve product photography performance while achieving differentiation in product design.

LatticePower achieves excellent color restoration capabilities from 300lm @ 1A ultra-high brightness,+/-350K color temperature range, and CRI>85. At the same time, suppliers who can combine their high precision lens processing capabilities to develop a series of flash module products and provide a complete set of solutions for mobile phone design manufacturers will be more likely to enter the supply chain system of mobile phone design manufacturers.

In the future, domestic manufacturers should have a strong belief and service awareness, bravely challenge international giants, and rely on ultra-high cost-effectiveness products to occupy the market. At the same time, we are constantly improving the quality of our products and the competitiveness of our technology, seizing the opportunities of the times, walking with the trend, and practicing the "Chinese Dream" of LED mobile phone flash!