voltage regulator for home use
Hi All,
I made a “little something” that was quite easy and might be of interest to some. It’s a tiny voltage regulator. You might ask, “Why would I possibly need something like that?” I pondered the same question until I was faced with a particular problem with no immediate solution. Once I circumvented my problem with this device I then began to recognize additional noteworthy applications.
While living in Germany, areas closest to the East German border became flooded with Russian “military surplus” shortly after the wall fell. Much of that was *state of the art* defense items at the time. Many, many Russian soldiers were abandoned by their native government as were military bases they had been conscripted to occupy and defend. Left with no way to be repatriated with their families in Russia, young soldiers had little choice but to remain on their respective military bases until food supplies were exhausted. Slowly they integrated into local East German societies bringing with them rather unique and interesting items. I quickly acquired the latest & greatest night vision rifle scope. American made versions were obtainable but they were old technology from the Vietnam era and still very expensive costing thousands of dollars. This particular Russian scope out-paced the American made Vietnam era scope by a “country mile”.
This scope uses out-of-the-ordinary NiCad batteries. Much like me they become old, exhausted, and untenable. Realizing this, and while the batteries still hold their charge, I measured their voltage. The scope’s housing for the battery pack was just large enough to house the American made 9 volt battery (rectangular battery with snaps at one end) with a slight bit of room to spare. Regrettably, the 9 volt battery is too powerful and will “blow” the electrical components rendering this scope worthless. I needed 6.2 volts to safely operate the scope. My way around this was to fabricate a tiny voltage regulator that would reduce voltage from 9 volts to 6.2 volts. The regulator is comprised of 5 tiny electrical components costing a whopping $3.75. It works like a charm.
Recognizing an immediate benefit from my labor and the work performed by the voltage regulator I began to see other applications. One such application was battery powered illumination although there are far more applications around the home. A small head lamp could run continuously for days using a small 9 volt battery pack as compared to hours (in the cold) when using tiny batteries designed for the head lamp. Similar correlations can be drawn for emergency radios (hand-held transmitters and ordinary transistor radio receivers). Even large hand-held flash lights are no exception, e.g., if weight is a factor when backpacking, heavy 1.5V D cell batteries can be replaced with a small 9V battery offering longer burn time and less weight to carry. I don’t mean to come off touting or advocating the use of a 9V battery. This is merely an example. Expand your vision! Even larger batteries, such as those used to energize electric fences on the farm, can be used in conjunction with the tiny voltage regulator providing days and days of illumination should normal household power be lost. Look around you. What battery sources are immediately available? Car and truck batteries? Tractor batteries? Road grader and bulldozer batteries? Why limit yourself to batteries? Why not use the tiny voltage regulator with wind and water generated electricity. Get my drift?
Ok, here’s what things you must know before fabricating this regulator.
1. What voltage is required to run your selected device. Is it 1.5V? Is it 6 volts? Is it 12 volts? If, for example, you’re running a hand-held flashlight that requires three D cell batteries or three AA or three AAA batteries, then knowing that each of these sized battery supplies 1.5 volts, then the total voltage is 4.5 volts. Alternately, voltage of a bulb is usually printed somewhere on the bulb so often times you can discern voltage directly from the bulb.
2. What is the value of your voltage supply. Are you using a 6V battery, a 12V battery, a 9V battery …….?
*Note! Batteries are DC (direct current) and not AC (alternating current) like that which comes from your wall receptacle. The regulator, soon to be shown, requires DC electrical power. Do not fabricate this device thinking it can be used with household power.
3. The last things you need to know are:
a) where to get the components
b) value of the components
c) the formula for determining value of components
d) the schematic or directions for connecting the components
I purchased my IC chip (brains of the regulator) from Digi-Key (Thief River Falls, MN ph# 800.344.4539). The current cost is $1.12. Remaining components were purchased from Radio Shack but I would advise that you purchase from Digi-Key or your local electronic supply store because most Radio Shacks will not have the *exact* components you need so make one trip do it all. Also Radio Shack usually sells in assorted bundles without knowing exactly what’s in the assorted packages.
My design is for use with a 9V battery or less. Chips utilizing higher voltage are easily obtainable. The chip should be an adjustable chip. The chip I selected provides Output voltage from 1.5V to 7V. *Important-Generally speaking, for an adjustable regulator to function properly, there should be a minimum difference of at least 3 volts between voltage supply and the desired supply. As an example my IC regulator will accept a maximum of 10V input delivering a maximum output voltage of 7V. The IC chip’s designed disparity is 3V. I chose to use a 9V battery with an output of 6V, hence, the required minimum of 3V disparity. Stated differently, though my IC chip is capable of delivering a maximum of 7 volts output, I could not use a 9V battery and expect to produce 7V output because disparity is only 2V. When using a 9V battery I can expect to realize 6 volts down to a minimum of 1.5V. If using a 10V source, I can expect to realize 7V down to 1.5V. Get my drift?
For this regulator you will need:
a) one IC voltage regulator Digi-Key part number 425-2689-5-ND
b) one 0.33uF ceramic capacitor designated as C1 in the schematic
c) one 47.0uF ceramic capacitor designated as C2 in the schematic
d) one 1000 ohm resistor designated as R1 in the schematic
e) one resistor (designated as R2) of yet to be undetermined value as this is the variable which determines Output voltage. Explanation for determining this value will soon follow.
f) one small piece of “bread board” or often called perforated board (can be found in size 3” x 3” which is more than sufficient).
g) access to a soldering gun and access to a VOM (volt ohm meter) both of which you should always have around the house!!
The formula for determining the value of R2 is not necessarily complicated provided you have retained your math skills. Although I will provide the original formula, I have reduced the formula to simplicity forgoing the need to recall math from years past.
The unadulterated formula is as follows for those seeking purity. I would, however, encourage the second formula as it’s a “Plug n’ Play” version.
Vo = Vref x (1 + R2/R1)
where:
Vo = voltage output
Vref = a constant of 1.25V
R2 = value of resistor
R1 = 1000 ohm resistor
The Plug n’ Play formula is as follows:
X = 1000 (Vo – 1.25)/1.25
where:
Vo = the desired output voltage
X = the value of R2 (resistor) that’s used to determine desired voltage
Example:
Using my selected IC chip, I desire to produce an output of 6V to run my ACME JewelMaster Thing-a’-jig. Since Vo = my desired output voltage (6V), I simply replace Vo in the formula with “6” and then solve for X as follows:
X = 1000 (Vo – 1.25)/1.25
X = 1000 (6 – 1.25)/1.25 *Note: remember anything in parentheses must be calculated first!
X = 1000 x 4.75/1.25
X = 4750/1.25
X = 3800
Thus to make the regulator produce 6V using either a 10V or 9V source, a resistor having a value of 3800 ohms must be used in the spot that’s designated as R2 in the schematic (which is soon to follow).
*Note: Nowhere in the formula was input voltage used in the equation. The regulator will accurately regulate output voltage, regardless of input voltage provided that input voltage stays within the maximum handling capacity of the IC chip and there is a 3V minimum disparity between input and output voltage.
Schematic
The following schematic shows where the components connect to one another. Battery connects to the + & - side on the left. Bulb (radio .... whatever) connects on the right .... Load. C1, C2, and R1 values are constant. R2 is the only variable and this is calculated using my Plug n' Play formula.
Enjoy,
Harold
