The circuit of Figure 3 (b) enables all calm the current flowing into the LED, but in order to match the electrical characteristics of each LED (Matching), particularly in the circuit set up a group Ballast resistor.
MAX1910 in Figure 3 (b) attributed to the constant current output type voltage regulator Although this circuit is the use of the same maker, the lot (Lot) white LED flashlight to obtain an excellent match, however, is not the same in the use of manufacturers and Lot LED, will be showing a lot of the characteristics of the difference between the spread. The current regu-Lator use the method similar to Figure 3 (a) to manipulate the drive current, but it can make the the Ballast resistor of the power consumption decreased by about half.
Figure 4 (b) test results show that the current white LED flashlight into six random sampling from 15.4mA to 19.6mA, very large scale change. Thus, vendor A and B party both CREE flashlight is uniform 17.5mA current drive. The disadvantage of this circuit is formed Ballast resistor power is lost there is danger of residues, and is unable to obtain the LED current matching; But the whole, the circuit to both initiatives characteristics and simplicity, and therefore have a considerable degree of use value.
2.3 Use of Multi pull current output regu-Lator drive
The circuit of Figure 3 (c) enables the current inflow LED flashlight respective calm, and thus does not require the use of Ballast resistor, current accuracy and matching Regulator assigned by the respective current regulator.
Figure 3 (c) of the MAX1570 IC can reach 2% of the specification of the current accuracy of the current regulation, with the specification of 0.3% current matching approach.
Current regulator is constituted by the MAX1570 IC Low Drop Out Type, so it's very high power initiatives. Figure 4 (c) test results show that the use of the drive circuit of Figure 3 (c), the inflow of the six randomly sampled calm white LED current is 17.5mA.
Despite the demand for the four convergence of terminal between ReguLator CREE flashlight, but this circuit does not require Ballast resistor, it is possible to effectively restrain the packaging area, which is very suitable for applications in the packaging space is extremely narrow in areas such as small LCD panel.