LED Down lights

Figure 4 Typical GaAsP forward voltage corresponding to the conduction current of InGaN Figure 5 Typical forward voltage corresponding to the conduction between the current

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Figure 6 Using the MAX1910/MAX1912 charge pump circuit for current regulation

    If VF VCC increases to more than 10 times, you can reduce the impact of changes in VF, but consumes more battery-powered products do not meet the demand. For a single-cell lithium-ion battery-powered systems, lithium-ion battery voltage variation range of 3 ~ 4.2V. If the white LED  Ceiling Light bias circuit simply by a lithium-ion battery and a current limiting resistor, the output brightness will produce significant changes. Reasonable solution should be using current bias circuit.

(A) current bias circuit

LED Down lights 

    Current bias circuit is actually using a white LED current source providing bias. If the current source has a sufficient dynamic range, this offset manner from VF changes. Figure 7 is a schematic diagram of the current bias scheme. The circuit in Figure 3 of the current limiting resistor with a current source instead. Light output intensity and forward voltage of the power supply and has nothing to do, as long as there is sufficient power to provide bias voltage for the LED. In Figure 7, Q1 to enable control switch.