Mobile phones can be regarded as one of the fastest-growing electronic products in recent years, and CPUs, GPUs, screen sizes, storage spaces, and camera modules have all developed rapidly. Among them, mobile phone flashlights have become more and more important as devices that effectively enhance the camera's camera photographing effects in dark environments. There are many types of mobile flash solutions available on the market. How to select the right flash device and solution depends on the performance of the camera module and the positioning of the mobile phone. Here we come to count the mainstream flash solution on the current market:

Figure 1. Mainstream flash solution

1) Ultra low false flash

This solution mainly uses large-scale packages such as the 2835 or 3014 used in large-scale backlights at present, and the drive current is relatively low, typically between 150 mA and 300 mA. This solution does not require a separate driver IC. Directly using the platform's current source or using a simple triode to set up the channel to drive directly from the battery, this solution is the solution with the lowest cost.

2) Middle 8M pixels, low current drive

This solution is mostly used on 8M-pixel mobile phones, and 8M cameras have gradually become the mainstream configuration of mobile phones. The 2016 LED plus a separate lens is the most used solution. LED performance is generally around 200lm @ 1A. Drive current between 500 ~ 600mA, you can use the less expensive Charge Pump to drive.

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

Different from the second type of solutions above, the 2016 LED performance requirements are above 250lm @ 1A, and the drive current is about 1A. In order to obtain high electrical efficiency, most of them use DC/DC drives. These products also have higher requirements for lens design and processing.

4) Over 10 million pixels, high brightness dual lamp solution

The biggest benefit of using the same color temperature dual lamp solution is that the appearance looks cool and the brightness is higher. The same current of 1A is distributed on two LEDs, so that the current density of a single LED is lower, the junction temperature rises less, the luminous efficiency is improved, and higher illuminance is obtained. The camera with more than 10 million pixels uses a Pixel size of 1.1um, and the sensitivity is relatively poor. All higher-brightness LEDs are the most direct and effective way to improve the photo-to-noise ratio of photos under low illumination.

5) Above 10 million pixels, high brightness module solution

Compared with single-lamp and lens-based solutions, the advantages of the module scheme are high performance and stability, no assembly accuracy, and relatively high single-cost, so only some high-end models are used.

6) Dual lamp color temperature module solution

Two different color temperature LEDs are packaged in one module, and white light of different color temperatures is mixed by adjusting the passing current of each LED. This solution must build a closed-loop system with the white balance of the phone camera. The need for additional software workload is technically difficult. If the software is not handled properly, it will produce counterproductive photo color effects.

Customer's main issues in mobile flash design

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

How to determine the LED drive current? LED drive current determines the illumination, the greater the current the higher the illumination. In the final analysis, the flash is used to serve the camera's camera function, so how much current LED needs, how much illumination depends on the speed of the camera we choose to use. Then according to the SNR and color saturation curve of the photograph taken to define the minimum illumination requirement of the camera module, the drive current value of the LED is obtained.

To optimize the thermal design, in the enclosed space inside the mobile phone, high-current driving can easily cause the LED junction temperature to rise above 100 degrees. Therefore, we must optimize the placement of LED devices, away from all types of analog devices, so as not to affect their work. At the same time, it is optimized on the PCB Layout to give full play to the heat dissipation effect of the PCB copper layer. The thermal simulation can be combined with the actual test of the junction temperature of the LED to improve the thermal design optimization.

In addition, a special mention is that the lens processing design requirements for LED flash are also very high, the design is better, and the processing technology must also meet the standard, otherwise it can not be achieved.

The development trend of mobile flash

The current mobile phone design has a very serious homogeneity, and the design of each phone is similar. All mobile phone manufacturers are actively seeking for differentiated designs. More and more mobile phone brands have put the focus of differentiated design on the mobile phone imaging system. The flash will certainly be an indispensable part of it.

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

The module scheme is a very good solution to the problem that the structural assembler has a large difference and the optical performance cannot be guaranteed. More and more mobile phone manufacturers are beginning to accept modular design.

Figure 3. Making the surface of the LED whiter in order to facilitate the designer's appearance color matching

Pre-filling light has a popular trend, it can meet people's self-photographing needs in low light conditions. This kind of application requires that the color reproduction of the photos taken is good enough, and the demand for high CRI comes into being.

Quality and trend, to practice the "Chinese Dream" of LED mobile phone flash

In the period when mobile phone products are becoming more and more homogenized, major brand manufacturers are committed to finding ways to differentiate themselves. Almost all mobile phone design companies have put more emphasis on the video system. More and more mobile phone brand manufacturers hope to have their own unique flash design solutions, which can improve the product's camera performance while achieving product design differences. Change.

When the LED flash reaches 300lm @ 1A ultra-high brightness, +/-350K color temperature range and CRI> 85 excellent color reproduction. With many years of experience in professional secondary optical design and high-precision lens processing capabilities, Xinxin Electronics has not only developed a series of supporting flash module products, but also can provide unique designs and complete solutions for different mobile phone brand manufacturers.