About this deal
Figure 1. Schematic of MAX16840 HB LED driver in a boost configuration for MR16 LED lamps. This configuration provides good compatibility with electronic transformers. Making the LED MR16 Lamp Compatible with the Electronic Transformer
The driver circuitry of the MR16 LED lamp can be adjusted so that it draws a constant current load from the output of the electronic transformer. No capacitance can be added to the electronic transformer's output, since this can prevent the MR16 LED lamp from acting as a constant current load. Moreover, the current drawn by the MR16 LED lamp needs to ramp up to the programmed current at a very fast rate. Specifically, it needs to jump to the programmed value within 3µs or 4µs. If it ramps up slower than this, then the electronic transformer may stop switching.The dimming performance (Figures 2 through 11) was tested with an LET75 and a Lutron® SELV-303P dimmer. An MR16 halogen lamp acts as a non-linear resistive load. When the lamp is cold, the resistance is low and it will draw high currents which support the operation of the electronic transformers. Once the lamp lights up, the filament gets hot and its resistance increases. A typical 35 W halogen lamp will draw 35 W of power at 120 VAC/230 VAC when it is powered by an electronic or magnetic transformer. Since the halogen lamp is a resistive load, the brightness will decrease if the line voltage drops from nominal; brightness will increase when the line voltage rises from nominal.
The driver circuitry of the MR16 LED lamp can be adjusted so that it draws a constant current load from the output of the electronic transformer. No capacitance can be added to the electronic transformer's output, since this can prevent the MR16 LED lamp from acting as a constant current load. Moreover, the current drawn by the MR16 LED lamp needs to ramp up to the programmed current at a very fast rate. Specifically, it needs to jump to the programmed value within 3 µs or 4 µs. If it ramps up slower than this, then the electronic transformer may stop switching. Figure 7: LED current waveform when powered by an LET75 with a trailing-edge dimmer at 120 VAC. The dimmer is set at maximum light output.
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Figure 7. LED current waveform when powered by an LET75 with a trailing-edge dimmer at 120VAC. The dimmer is set at maximum light output.