Led Controller

1 Overview

LED devices during training, the intensity of light emitted by the current flowing in the decision of diodes. Figure 1 is a source of tension and polarization current limiting resistor consists of a simple, flowing through the LED current by the following formula: = IDIODE (VCC-VF) / [+ rlimit RDS (ON)] From This way, more expensive than low Hp laptop battery , but the different diode VF (forward voltage) parameters for the same thing. Figure 2, Figure 3-25 a„ƒ LED forward voltage (typical value) and the current curve. Can be seen from the current indicators: For the GaAsP diode, VF can be up to 2.7 V (+40%) for InGaN diodes, VF can be on the program to 4.2 V (+20%) . HP Pavilion dv2000 battery (HP dv2000 battery), HP HSTNN-LB31 Battery, HP EV088AA battery, if the system needs more LEDs, such as cell phones back display 8 LEDs, the design of Figure 1, take more than the current limit resistance, cover an area large circuit board. Toshiba PA3191U-PA3191U-Toshiba 3BRS 4BRS

If Vcc is increased to more than 10 times VF VF could reduce the impact of changes, but consumes more, did not meet the demand for battery products. Using a single system Li + + voltage range of the Li is 4.2 ~ 3V. If the LED bias circuit simply by Li + and provide the current limiting resistor, the output will be significant changes in brightness. Reasonable alternatives should be based on the circuit bias current.

2 Circuit bias

bias current of the circuit is actually a source of energy to be supplied by the LED. If the power source has sufficient dynamic range, this method will not offset the impact of changes in VF. Figure 4 shows the layout of the current program offset. The circuit in Figure 1, the current limiting resistor with an alternative energy source. The intensity of the emitted light and direct voltage independent, as long as the voltage is sufficient to provide a source of bias current and the LED may be. HP EV088AA battery , Figure 4 in order to be able to control switch Q1.

MAX1916 LED driver chips, and other special offers, through an advanced circuit current of the LED. In the tiny SOT23 package MAX1916 includes three groups of the current source, current flows through a mirror RSET for 3 outputs, Figure Pavilion dv2000 battery 5.HP (HP DV2000 battery), HP HSTNN-LB31 Battery, HP EV088AA battery, several circuits are the same phase gate MOSFET - the source of electricity, so they channel the same current, the current size of the decision by the ISET current mirror. MAX1916 offset maximum current of ± 5%, the factor "image" that the 200A / A. In other words, when the ISET of 50μA, each output current 10 (1 ± 0.05) mA (max). Toshiba PA3284U-1BRS PA3285U-1BAS

MAX1916 drain-source resistance in the range of temperature for a maximum of 50Îc, a current of 2mA LED GaAsP work to ensure the minimum required for the normal operating voltage: VF 100 mV to 2.71V input voltage can be GaAsP voltage protection LED 2.7V For a pressure drop and increase the current production, the MAX1916 can produce form factors of three parallel "mirror" of the current source 600, shown in Figure 6, parallel drain-source resistance of 50 / 3 = 16.67Îc (max). This connection allows a single white LED at 20mA 3V supply when the current reaches more than respond to existing products, such as backlighting requirements of the portable cellular phone. Used to set the end of the voltage source can be strong with a load capacity of the main power separately, for example, cell phones, VSET may be radio frequency (RF) v.