Low current LED application is simple, linear economy and strong constant current voltage stabilizing scheme

With energy saving, long service life and rich color combination and other advantages, LED has become one of the fastest growing semiconductor industry in recent years, the compound annual growth rate (CAGR) up to 20%, is expected in 2012 the global LED market value will reach $11 billion 400 million, is very promising in the future.

The typical LED driver includes two kinds of market, namely linear drive and switch driver; further, there are three kinds, respectively is the switch driver regulator, linear regulator and resistor type. These three drivers are suitable for different levels of current applications, see figure 1. As the current application current is more than 500 mA using the switching regulator, because linear actuator is limited to their structure, unable to provide such a large current; while in the current lower than 200 mA in the current application, usually adopts the drive linear regulator and resistance type; while in middle current application of 200 to 500 mA, can be used linear regulator, switching regulator can also be used. Figure 1: LED drivers for different current ranges.

Switching regulator with high energy efficiency, and provide excellent brightness control. Linear regulator structure is relatively simple, easy to design, to provide constant current and over-current protection, with an external current set point, and no electromagnetic compatibility (EMC) problem. Resistive drive uses a simple discrete device such as resistance to limit the LED series current, is an economical LED driver scheme, the same is easy to design, and there is no EMC problem.

A Morimi semiconductor as high performance, high efficiency silicon leading global solutions provider, to provide a switching regulator and linear regulator choices for different LED application. At the same time, customers on the market also need a kind of drive than the switching regulator and the general linear regulator economy, but the performance is much higher than the resistance drive. In this case, the use of patent pending A Morimi semiconductor self bias transistor (SBT) technology, combined with their own strong ability to control the process, launched a new LED drive scheme of discrete linear constant current regulator (CCR), to fill the gaps in the market, and further enrich the drive LED semiconductor A Morimi broad the lineup.

Low current LED application low current LED application and comparison of drive new linear constant current regulator for 20 mA to 200 mA. Such as in automotive applications, the current requirements of the combined taillight is usually only tens of MA (mA). In addition, in the billboard text circuit, backlight display and other commercial and industrial applications, the input voltage is usually as high as 30 Vdc, while the LED current in the range of 20 mA to 150 mA. In decorative lighting, working lights, landscape lighting, lighting and other buildings and general lighting applications, the input voltage is usually 12 to Vac or 120/220 Vac, and LED current is only between 20 to 100 mA. In addition, refrigerators and washing machines and other household appliances also use LED as a small LCD display backlight or alternative lighting bulbs, such applications also require low current LED driver.

In low current LED applications, although the driver resistance type is of low cost and simple structure, but the driver under the condition of low voltage, low current, LED will lead to insufficient brightness, and the load dump transient conditions, LED may be damaged. Moreover, this solution requires proper LED coding (binning), large resistance inventory, and low energy efficiency.

Compared with drive resistor, linear constant current regulator provides a stable current, providing constant brightness in wide voltage range under the protection of LED in high input voltage, so as to avoid driving, providing higher brightness in low input voltage. Thanks to its constant current characteristics, customers can reduce or eliminate the cost of coding different LED from different suppliers, so that the total cost of the system is lower.

Figure 2:CCR combines a resistive drive with a linear regulator director to fill the market gap.

We can verify the performance comparison of the two drive through the actual test, see figure 3. In the test, we compared the combination of two kinds of actuators to achieve the combination of taillights, where the CCR is a stable current of 25 mA devices. As can be seen from the figure, when the same input voltage of 9 V, the CCR is higher than the current of the resistive drive, making the LED more bright. 13 V at the same voltage input, the brightness of the same two. When the voltage is higher than 13 V, the current of the CCR is gradually stabilized to a current of 25 mA, while the current of the resistance type driver has been rising, which can cause the LED to be driven, thereby damaging the LED. In addition, CCR provides the current accuracy of + 10%, fully meet the application requirements, and the resistance of the current accuracy of only + + 50%, far from. Figure 3: comparison of the V-I curves of a resistive drive with a constant current of 25 mA.

Based on patented SBT technology is simple, economic and robust linear constant current regulator A Morimi semiconductor constant current regulator self bias transistor based on patent pending A Morimi semiconductor (SBT) technology, providing certain degree integration, and combined with the super A Morimi semiconductor process control ability, low current application provides a simple (Simple), economy (Economical) and strong (Robust) LED driver solution.

Specifically, double end this device is easy to design, suitable for high-end and low-end (High-side) (Low-side) application, without the need for external components, very simple. Its economy is mainly reflected in the elimination of LED coding, reduce inventory costs, as well as the protection of LED, reduce replacement and maintenance costs. A Morimi semiconductor also plans to launch three terminal adjustable output linear constant current regulator, it