Midget Emergency Torch Circuit
Here is a tried and tested design of an ultra-simple emergency torch
built around the inexpensive dc-dc converter chip MC34063. Beyond a
handful of simple components, a lithium coin cell and a small key fob
case no additional parts are needed!
The MC34063 (IC1) is a monolithic control circuit containing the
primary functions required for dc−to−dc converters. MC34063 consists of
an internal temperature compensated reference, comparator, controlled
duty cycle oscillator with an active current limit circuit, driver and
high current output switch.
This chip was specifically designed to be incorporated in buck and
boost (and voltage−inverting) applications with a minimum number of
external components. Here, the IC-MC34063 is used to drive three
high-efficiency white LEDs using 3V dc supply available from the
built-in CR2032 lithium coin cell.
In this circuit, designed to drive ultrabright white LEDs at constant
current, IC1 (MC34063) compares the external voltage at its pin 5 with
an internal reference voltage of 1.2 V in order to stabilize its output.
Here, resistor R3 (connected to pin 5 of IC1) sets the operating
current of the series-connected white LEDs (LED1-LED3). Note that the
circuit can provide a variable intensity by making R3 to be a variable
resistor. If R3 is linear then the perceived light intensity will be
approximately linearly variable with the variable resistor’s shaft
position.
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