Voltage Regulator


Posted on Sep 27, 2012

This regulator is suitable for devices that need up to 1mA. For higher output current, the resistors would have to be scaled down in reverse proportion to the peak current expected. With the resistor values shown, the regulator draws a current of only 0.015mA, which means that a typical SR44 silver oxide cell would last for about one year and three months powering it. Adding the current actually consumed by the camera, you might expect a typical battery lifetime of close to one year. The output voltage measured in the lab varied from 1.39V for zero load, to 1.34V at a load of 1mA. This seems acceptable even for the most critical applications.


Voltage Regulator
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The silver oxide cell provides the reference voltage, so the output voltage will vary in proportion to the cell voltage. For this reason, the actual output voltage will vary over the life of the cell. But in any case, it will be a lot better than using a Schottky diode! It would seem attractive to include a real voltage reference in the circuit, so that it could be used with an alkaline cell and keep the output voltage constant even when the cell drops. The problem is that it's not easy to implement a stable voltage reference that has very small internal current consumption, specially when the available input voltage is as low as here! Such a circuit would probably be feasible only when there is a power switch between the battery and regulator, so that the higher consumption of the regulator is no longer that important. If you want to build this circuit, here are some hints: - The transistors I used are by no means optimal. I used them simply because I had them lying around on the desk. If you want to look for better ones, Q1 and Q2 are small signal NPN transistors that should have an Hfe as high as possible, at very low collector current. These transistors are working at only some microamperes of collector current, which should mean a base current of only a few tens of nanoamperes! Q3 is a small signal PNP transistor, that also should have a high Hfe at low current levels and low collector-emitter voltage, but it...




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