<not sure about the etiquette in regards to old threads, but since this is a sticky, and I have some info that may help people out in the future>
There are ways to convert lighting over to LEDs
without having to put a series load resistor to emulate the resistance of a filament.
-A quick lesson on why low current devices cause hyperflashing (see http://i.imgur.com/AZVrxv9.gif)
-most timing circuits use a 555 chip that internally compares two levels of voltage (high is defined from 2/3 vcc to vcc and low is 0 to 1/3 vcc)
-a flip flop circuit that is tried to the output of the chip will change from low to high depending upon the voltage seen on the op
-the time it takes for the circuit to reach ~63.2 % of VCC is known as the RC time constant tau (
) and directly dependent upon resistance and capacitance of the circuit
pull less current than filaments, the flasher unit thinks there is a blown light circuit henceforth hyperflashes
One way to compensate is swapping out the resistor (to a higher value) within the flasher itself to slow the flasher unit down.
Another way which neglects any power savings but results in more ideal current regulation and higher light output, involves usage of transistor downstream in whats known as a current mirror (see http://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/current-mirrors/)
The way the current mirror works is by using a bias voltage between the collector (top most leg shown in the diagram) and the base (middle straight leg), as well as a gain factor beta (β)
. For a standard Bipolar Junction Transistor, the voltage between the base and the emitter (bottom most leg, denoted by the arrow) is 0.7 volts. What this means is the voltage on the base leg(s) will always be 0.7 volts higher than the emitter and VCC will be the base voltage plus the voltage dropped on the biasing resistor. The amount of current going through the bais resistor is typically the gain factor beta plus the current going into the base, but since the gain factor is usually orders of magnitude greater the base current can be disregarded.
Voltage (of the) Collector (leg)= VCC-(β)( Bias resistor)
Voltage (of the) Base (leg) = Voltage (of the) Collector (leg)
Voltage (of the) Emitter (leg) = Voltage (of the) Base (leg) -0.7 Volts
Or in one equation: VCC-(β)( Bias resistor)-0.7 Volts =0 Volts
The goal of this circuit is, since all the base legs are tied together, the voltages on the other legs must also be the same, therefore the currents will also be same (this is based upon usage of similar components being used). In this configuration, the sum of the currents should add up to the point where the flasher unit will see a current similar to a filament system.
Hope this info helps you guys out.