- #Led flashlight driver circuit schematic driver#
- #Led flashlight driver circuit schematic upgrade#
- #Led flashlight driver circuit schematic plus#
- #Led flashlight driver circuit schematic series#
T2 now experiences a loss of triggering voltage and switches OFF, restoring the LED back to its original state via T1, until again the restriction process is initiated and this continues, maintaining a current controlled illumination over the connected LED, which is a Cree XM-L 10 watt lamp in this case. The LED is now forced to shut down, however the process as the LED tries to shut off it also begins reducing the voltage across the particular base resistor of T2. If this sensed voltage exceeds 0.7V, T2 is forced to trigger and ground the base potential of T1, thereby restricting its conduction, and subsequently restricting power to the LED. This induces a proportionate amount of voltage across this current sensing resistor, which in turn forms the triggering voltage for the base of T2. The process allows the entire current consumed by the LED to pass through one of the selected resistors (R2, R3, or R4) to ground. When the circuit is switched ON, T1 is triggered via R1 illuminating the LED. Referring to the above diagram, the design is a basic current controlled stage where T2 determines the maximum current limit of T1 by controlling the base potential of T1. Although it's not one of the most efficient of the designs, the simplicity wins over the slight inefficiency. The design can be implemented using the following transistorized current control stage.
#Led flashlight driver circuit schematic driver#
Do you have any advice on the battery voltage I should choose and how would I achieve changing the intensity of the LED to a high, medium and low state with the existing on/of switch?įor a battery operated circuit the LED driver could be simply in the form of a current controller stage, because here voltage regulation is not important and can be eliminated.Īs per the above request, the Cree XM-L T6 LED driver is required to be operated from a 3.7V/3amp source, with a 3-way switchable dimmer control facility.
#Led flashlight driver circuit schematic upgrade#
I would like to retrofit my 3 cell Maglite with this Cree LED and upgrade the batteries to Li Polymer. But with the capacitor in place, the circuit keeps working better when the cell is almost fully discharged and its internal resistance gets higher, so it’s better to include it.Thanks for the great advice and circuits! Have you had a chance to have a look at a circuit for the LED mentioned by Guruh? With a good NiMH cell, the circuit works the same without it, so you can save a few cents here. If anyone wants to build this circuit to run 24 hours a day for 30 years, it would be good to pick a capacitor rated for low ESR and a relatively high ripple current, but for flashlight use a plain standard 47♟, 35V electrolytic capacitor works great.Ĭ1 is not strictly necessary. C2 has to eat the load pulses that start at about 1A, and has to keep the voltage constant enough to feed the LEDs an almost smooth DC.
The oscillating frequency is 30kHz, and the transformer operates at a peak flux density of 0.1 tesla, far away from saturation, and low enough to have very low loss. During operation this pulse is about 24V high, so that the feedback winding develops -4V, which results in applying about -3.3V to Q1’s base, enough to switch it off very fast, but not enough to make the base reverse-conduct.Īs soon as the transformer has fully discharged into C2, the voltage on it breaks down, and the transistor enters conduction to start a new cycle. The collector voltage will soar as T1 forces current to keep flowing, until D2 starts conducting and discharges the transformer into C2, by means of a quite narrow pulse. This very quickly puts the transistor into blockage. At this point the transistor will start getting out of saturation, which makes the feedback voltage drop. This base current keeps the transistor in saturation until its collector current reaches approximately 1A, while the transformer loads up. D1 is not conducting a significant current at this time, because the transistor clamps the base voltage to 0.7V and the 3 turn winding subtracts 0.2V from this, so that we end up with only 0.5V across the diode.
#Led flashlight driver circuit schematic plus#
At this moment there will be a base current defined like this: The 1.2V of the cell, plus the 0.2V induced in the feedback winding, minus the 0.7V base-emitter drop of the transistor, make a total of 0.7V, which applied to the 22 ohm resistor gives about 32mA base current. That causes a current through the 18 turn winding, and thanks to the positive feedback the transistor is driven into saturation. When switching it on, R1 and D1 bias the transistor into the linear range, through the feedback winding on T1.
#Led flashlight driver circuit schematic series#
In this circuit are 7 series LEDs so we need a driver circuit that will provide about 23V at 20mA, when fed from a 1.2V NiMH rechargeable cell or from a 1.5V alkaline cell. This makes for a power of about 66mW per LED. A typical white LED has its best power-efficiency combination at about 20mA, and needs about 3.3V. The single cell led flashlight circuit is a self-oscillating boost converter.