Illumination sources, each including at least one light emitting diode, are connected either in series or in parallel by a switching circuit, depending upon an applied input voltage. The switching circuit switches the illumination sources from series- to parallel-connection, or vice versa, when the applied...http://www.google.com/patents/US6670776?utm_source=gb-gplus-sharePatent US6670776 - Enhanced trim resolution voltage-controlled dimming LED driver
