Introduction
After some fooling around with batteries every hobbyist should think seriously investing into a decent power supply . You could buy one of course but if you would be a lot more rewarding to build your own and save yourself a bundle . Aside from saving a lot of money , you will also get to know what is inside your supply and be able to service it if anything goes wrong down the road .
Within the following descriptions of the power supply , you will be able to chose many options available to upgrade your project into a really versatile high precision instrument , such as a variable voltage output , presettable digitally selectable voltages , a current limiting function , digital LCD or LED read outs , or just a basic accurate power supply .
After some fooling around with batteries every hobbyist should think seriously investing into a decent power supply . You could buy one of course but if you would be a lot more rewarding to build your own and save yourself a bundle . Aside from saving a lot of money , you will also get to know what is inside your supply and be able to service it if anything goes wrong down the road .
Within the following descriptions of the power supply , you will be able to chose many options available to upgrade your project into a really versatile high precision instrument , such as a variable voltage output , presettable digitally selectable voltages , a current limiting function , digital LCD or LED read outs , or just a basic accurate power supply .
The Basic Circuit
The circuit shown below is the basic variable supply using the LM317 adjustable regulator with RV1 being the main adjustable element to produce a regulated voltage output from 1.2 volts to a maximum of 37 volts at 1.5 amp current when used with a heatsink .
If only the basic supply will be build , then, use only RV1 and connect it directly to ground marked "B " . But you migh still be interested into using the LCD readouts and current limiting function as described further , so read on .
With the additional components RV2 to RV5 and Q1 to Q5 we expand the one variable function privided by RV1 into four additional switchable preset voltage range for for fast highly accurate selectable voltage outputs .
You are going to ask "why don't we do away with Q2 - Q5 and connect the trimmers directly to the switch" Well we want precision and we cannot guaranty the switch contacts will not eventually build up resistance and affect the trimmer setting . By using transistors we can be assured that the setting will not drift even if the transistor base voltage from the switch may drift a few milivolts . You can omit the transistors if you wish but they are essential for the proper function of the push button circuit .
A list of parts is availble for your requirement to be selected depending on your application of the project . All transistors used are the 2N2222 or 2N3904 or equivalent NPN type .
The circuit shown below is the basic variable supply using the LM317 adjustable regulator with RV1 being the main adjustable element to produce a regulated voltage output from 1.2 volts to a maximum of 37 volts at 1.5 amp current when used with a heatsink .
If only the basic supply will be build , then, use only RV1 and connect it directly to ground marked "B " . But you migh still be interested into using the LCD readouts and current limiting function as described further , so read on .
With the additional components RV2 to RV5 and Q1 to Q5 we expand the one variable function privided by RV1 into four additional switchable preset voltage range for for fast highly accurate selectable voltage outputs .
You are going to ask "why don't we do away with Q2 - Q5 and connect the trimmers directly to the switch" Well we want precision and we cannot guaranty the switch contacts will not eventually build up resistance and affect the trimmer setting . By using transistors we can be assured that the setting will not drift even if the transistor base voltage from the switch may drift a few milivolts . You can omit the transistors if you wish but they are essential for the proper function of the push button circuit .
A list of parts is availble for your requirement to be selected depending on your application of the project . All transistors used are the 2N2222 or 2N3904 or equivalent NPN type .
Options
The Transformer :
The LM317 will regulate a voltage to a maximum of 37 volts under load and needs at least 1.5 volts above the required regulated voltage , based on this you must use a transformer which will output the required voltage and at a current output to meet your requirements . A center tapped or two wires output transformer may be used.
The rectifier bridge may be substituted with four single rectifier diodes . If you are in doubt about this please go to Introduction for more informations on this subject .
As shown on the Layout RS1 and RS2 are precision resistors used as shunts for the Current meter if used , if not , they can be omitted and the voltage output taken directly from the " OUT " position pad .
Since the LM317 has built in overcurrent shut down function the Fuse may be optional but it is a wise investment .
The Heatsink used is a vertical type , the larger you can fit , you can buy or make your own using 1/8" thick copper or aluminum plate about 1.5" square bolted to the regulator , no other support should be required .
Source: http://members.shaw.ca/roma/supply-4.html
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