In the previous post we learned an SMPS design which can be used for driving a 50 watt LED lamp made from 50 numbers of 1 watt LEds. Here we try to understand the connection details of the LEDs with the driver circuit.
The Circuit Configuration
Assuming we want to use 1 watt LEDs (recommended) for the proposed 50 watt street light, we would require 50 numbers of these LEDs to be configured with the circuit.
Referring to the previous post, we see that one of the outputs is specified with 105V at 350mA.
This particular output becomes the preferable one for driving 50 numbers of 1 watt LEds, although it could be implemented only after through some serious calculations.
If we connect all the 50 LEDs in parallel would call for an output equal to 50 x 3.3 = 165V, but since this output doesn't seem to be available, we could opt for a more feasible series/parallel connection with the LeDs.
So we can make two strings of LEDs, each consisting of 25 nos of LEDs, and connect these two strings in parallel.
However, involving two strings would mean that the LEDs would now require 3.3 x 25 = 82.5V @ 700mA
The above values once again seem to be not matching the driver output specs.
No issues, the above values can be matched by doing a few simple tweaks with the relevant output winding of the driver transformer.
Current Level Adjustment
The current (amps) can be increased by replacing the N2 winding with a bifilar winding consisting of two 28AWG wires wound simultaneously.
This will take care of the required 700mA current since now we have used two wires in parallel for N2 instead of the recommended single wire.
Next, for reducing the voltage from 105v to 82.5V, we simply need the above winding to be made into 24 turns instead of the indicated 31 turns.
That's it, once the above couple of simple tweaks are done, the driver now becomes perfectly suitable for driving the proposed 50 watt LED lamp module.
The LED connection details can be witnessed in the following schematic diagram: