Shanghai Longmao Microelectronics Co., Ltd. recently launched several dimmable LED fluorescent lamps. Although the fluorescent lamp of the past has a relatively high luminous efficiency, it contains a highly toxic substance, mercury, and it cannot be dimmed. Now LED luminous efficiency has caught up with and surpassed ordinary fluorescent lamps. Under the same brightness condition, the input power of LED fluorescent lamps can be reduced by half, and it does not contain toxic substances. It is a new environmentally friendly light source. Not only that, LED is a device that is very easy to change its brightness, as long as a pulse width modulation (PWM) signal is input, it can be dimmed, so Longmao has introduced three dimmable LED fluorescent lamps.
The first one is to manually dim the LED fluorescent lamp. In many cases, it is necessary to manually adjust the brightness of the LED fluorescent lamp. This manual dimming fluorescent lamp uses the same knob as the ordinary incandescent lamp, which is installed at the light switch, but unlike the incandescent lamp. SCR is used, so it will not cause interference in the power line. It is just a low level PWM signal generator. The required dimming signal is generated and sent to the dimmable boost type constant current driving source SLM2842SD, and then sent to the LED fluorescent lamp for dimming. The block diagram is as follows:
The second type is the photosensitive dimming LED fluorescent lamp. In many occasions, the ambient light changes at any time. For example, in the office by the window, in the sunny weather, it will be very bright. At this time, the brightness of the fluorescent lamp is not so high. Bright, after using the LED light bulb with photosensitive auto-dimming, you can dim it on sunny days and brighten it in the rainy weather, so you can further save energy. In addition, the fluorescent lamp in the subway car has a similar situation. In the urban area, the subway is usually operated underground, and the interior of the car requires a large brightness. In the suburbs, the subway usually opens to the ground. At this time, the outside brightness is very bright, and there is no need for internal lighting. If the photosensitive auto-dimming is used, the brightness in the car can be automatically adjusted.
Its composition principle is similar to manual dimming, except that the manual dimming knob is changed into a photosensitive element, and the PWM signal generator is changed to use a single chip microcomputer to generate a PWM dimming signal. 
The second type is the photosensitive dimming LED fluorescent lamp. In many occasions, the ambient light changes at any time. For example, in the office by the window, in the sunny weather, it will be very bright. At this time, the brightness of the fluorescent lamp is not so high. Bright, after using the LED light bulb with photosensitive auto-dimming, you can dim it on sunny days and brighten it in the rainy weather, so you can further save energy. In addition, the fluorescent lamp in the subway car has a similar situation. In the urban area, the subway is usually operated underground, and the interior of the car requires a large brightness. In the suburbs, the subway usually opens to the ground. At this time, the outside brightness is very bright, and there is no need for internal lighting. If the photosensitive auto-dimming is used, the brightness in the car can be automatically adjusted.
Its composition principle is similar to manual dimming, except that the manual dimming knob is changed into a photosensitive element, and the PWM signal generator is changed to use a single chip microcomputer to generate a PWM dimming signal.
The third dimmable LED luminaire is not necessarily in the form of a fluorescent lamp, but can be any type of high power LED luminaire, mainly used in tunnel lights. In the application of tunnel lights, it is also necessary to adjust the brightness of LED lamps according to day, night, sunny or rainy days, which requires a device capable of dimming from a long distance (several kilometers to tens of kilometers). Shanghai Longmao Company also successfully solved this problem and proposed a very reliable system for long-distance dimming.
All three dimming devices are now patented.
The LED fluorescent lamps used are high-brightness SMD LEDs with a thermal resistance of only 45oC/W, and lamps with semi-aluminum heat sinks. Since the driving Power Supply is external, it can be fully dissipated without built-in space. The aluminum alloy tube of the sheet improves the heat dissipation efficiency, and also avoids the light decay of some LEDs caused by the heat of the built-in power source, thereby reducing the junction temperature of the LED, prolonging the life of the LED, and ensuring a service life of 50,000 hours. Moreover, the AC power supply adopts an isolated switching power supply, which can fully withstand the test of CE high voltage and also remove the possibility of electric shock. This type of fluorescent lamp has begun to be produced in small batches to meet the needs of a wide range of users.
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