# 13v linear regulated power supply

Is it possible to design a very basic linear regulated power supply that can control an output of 13 volts? I ask because doing a thorough research online leads to very complicated designs.

• 1st question. How much current? 2nd question. What have you found so far (which you consider complicated)? – Nick Alexeev Nov 12 '12 at 4:37
• First off, thanks for the response. Any thing 1A and below would be just fine. I want it to be as light as possible but all my research were leading me towards the use of transformers, which I dread using. – Jeffrey G. Nov 12 '12 at 6:25

You can easily make a 13V low current linear regulated power supply with the LM317. The LM317 is a programmable regulator that has the output voltage set via a pair of resistors that form a divider from the output to GND. A simple power supply would consist of these two resistors and two capacitors, one at the input and one at the output. The following picture shows the circuit for an LM317.

For a 13V output you will want an input voltage 16V or more. A typical current value to use for the IADJ is 50uA as can be determined from the part data sheet. For a 13V output you can use the formula in the picture to get the resistor values. If you use precision values of R1=274 ohms and R2=2550 it is possible to achieve an output of almost exactly 13V when the IADJ value is 50uA.

• Thanks a lot Mike. Does the LM317 handle input of about 230 volts. I dont want to use transformers – Jeffrey G. Nov 12 '12 at 6:21
• @JeffreyG. Linear voltage regulators are not designed for input voltages in the hundreds of volts. Keep in mind that for your requirement, the regulator would need to dissipate (230 - 19) = 211 volts at up to 1 ampere = up to 211 watts as heat. This is a huge amount of heat generated, totally impractical for linear regulators. Consider using a 15 volt wall wart instead, and regulate its output to the required 13 volts. – Anindo Ghosh Nov 12 '12 at 7:16
• @anindo-gosh thanks. What about say I increase my output current expectations, would it still be feasible? I kinda want to build a power supply so it will have to be connected to the mains. – Jeffrey G. Nov 12 '12 at 7:39

From the question, and comments by the OP to another answer, the requirement appears thus:

• 230 Volts AC main line power as input
• 13 Volts DC regulated 1 Ampere as output

A suggested practical solution with minimal complication is as follows:

• Use a wall wart or laptop brick power supply with 15 to 18 Volts DC output, rated for 1.5 Amperes or thereabouts. Regulation quality is not critical.
• Use an adjustable linear voltage regulator circuit such as the LM317 suggested by @MichaelKaras in another answer, to obtain the regulated 13 volts output. Using a suitable heat sink on the LM317 is recommended.
• The LM317 has a drop-out voltage at or under 2 volts for 1 Ampere load, under normal working temperatures, so this will work with a 15 volt input.
• Thanks a lot @anindo for putting the whole thing into perspective. You honestly rock and Michael too. Well, I'm still experimenting other stuff. Do you guys think using a zener will even less complicate the whole thing? – Jeffrey G. Nov 12 '12 at 8:22
• @Using a Zener diode would require finding the right Zener, computing and incorporating some resistors, besides the smoothing capacitors - and would result in poorer regulation (more ripples / voltage dips on load) than a dedicated regulator IC. I would not recommend zeners if you just want to get good regulated power, and move on to building your actual project. – Anindo Ghosh Nov 12 '12 at 8:31
• Good answers already posted but why not use a wall wart with linear voltage adjustment knob? They are available around $10 to$20. – ExcitingProjects Nov 12 '12 at 9:02
• @anindo ok i'd settle for an ic then for the final project. Also i'm not really going to use any load, i just want to prove it works since 13 is really not the standard. Thanks a lot. I'll still try out the zener idea later. – Jeffrey G. Nov 12 '12 at 9:52
• @ExcitingProjects I know right? But then it would take all the fun away from building it myself and understanding how it really works – Jeffrey G. Nov 12 '12 at 9:55