CONSTANT CURRENT LOW MODE CIRCUIT

摘要

For applications where some sort of beam is required and where compact dimensions, the ability to cope with extremely rough treatment and the ability to continue to provide emergency level lighting as batteries approach exhaustion is important, the halogen bulb level efficiency of white LEDs becomes acceptable.rnUnfortunately, in order to produce a predictable light output, as well as remain inside the maximum current and thermal dissipation ratings of the devices, it is necessary to operate them with a series resistance, which can reduce overall efficiency by as much as a factor of two, depending on the expected range of operating voltages. To limit this by using a battery with the lowest suitable voltage leaves a little leeway to supply the required constant operating current at the fairly 'stiff operating voltage of around 3.6V (a set of four Ni-MH cells could range from 5.8V straight out of the charger to under 4.4V, as the batteries approach exhaustion).