In recent years, due to the increasing attention to the performance development and energy saving of LED, LED is used for lighting, backlight of ultra-thin TV and other purposes. It is expected to be widely used as the light source of various equipment in the future. The high brightness LED can be used as the light source for camera photography. Nowadays, portable devices such as smart phones, digital cameras and digital cameras are equipped with high brightness photography light source LEDs, which are used as the torch light in animation photography and the flash in still photography. Due to the continuous improvement of LED performance in the future, it may be more widely used for shooting scenes.
LED flash and topics
LED has this feature, and its brightness is adjusted by controlling the amount of current and time. Therefore, it is suitable for shooting scenes, making it possible to widely use the flash in still photography and the torch light in dynamic photography.
Figure 1 (left) shows the general LED flash circuit structure. The power supply of LED is battery, so the current flowing into LED is restricted by the performance of battery. Therefore, the brightness is also restricted. In order to match the improvement of LED performance and photography, brighter luminescence is required, so a large current must flow to the LED. Here, Fig. 1 (right) shows a circuit structure in which an electrical double-layer capacitor (EDLC) is used as an auxiliary power supply. In this circuit, the large current that cannot be provided by the battery can be provided by EDLC, so it has nothing to do with the limitation of the battery, and the LED can emit more brightly.
Figure 1: circuit structure of LED flash (left: no EDLC, right: EDLC used)
Figure 2 shows the data when 8A current flows into the LED as the auxiliary power supply. The result is a brightness of more than 1000 lux.
Figure 2: luminous characteristics of LED driven by high current (8a) using EDLC
The EDLC of Murata production Institute, which is most suitable for LED flash system
In order to provide high current to the LED in a very short time, the characteristics of charging particles used as auxiliary power supply require large capacity and low internal resistance. In addition, in order to provide stable current in different environments, low and stable internal resistance in a large temperature range is also a necessary condition.
EDLC can achieve large capacity because, in principle, the power storage structure without chemical reaction can reduce the internal resistance compared with the battery. The EDLC produced by Murata is the most suitable electrode material and structure. Although it is a small, ultra-thin and light package, it realizes low resistance (tens of M Ω) and large capacity capacitor in a large temperature range. Therefore, high current a can discharge with low loss in a large temperature range. Therefore, the LED can be provided with a large current of more than 2a, which is difficult to be provided by the battery of a general portable device, from tens of milliseconds to hundreds of milliseconds（ (refer to figure 3)
Figure 3: discharge characteristics (2.7v/700mf/30m Ω product)
Table 1 shows the list of EDLC products produced by Murata production Institute, and Figure 4 shows the ledflach demonstration board using EDLC of our company. The system can provide a large current of up to 8A to the LED in 33 milliseconds（ Controllable at 2a-8a / 10-60ms)
Figure 4: LED flash demonstration board using EDLC
LED is widely used as a photography lamp in smart phones and digital cameras. In these machines, EDLC is used as the auxiliary power supply of LED, which can realize brighter flash. On the other hand, the digital camera uses the hernia tube flash system, which has the characteristics of easy control, power and space saving, and is expected to replace led. So far, circuit systems that can pass large current and LEDs with high luminous rate need EDLC with large capacity and low resistance.
The use of equipment equipped with cameras is expanding and is expected to occupy a more important position in our life. Our company will continue to study the characteristics of products, continue to propose small, thin and light packaging EDLC with large capacity and low resistance, which is most suitable for driving LED, and continue to contribute to improving the convenience of camera equipment.
Responsible editor; zl