what is the best power supply configuration here

Thread Starter

clangray

Joined Nov 4, 2018
25
Hi,

I have a pretty simple circuit in mind of 6 IR-LEDs in series, and a ballast resistor, powered by a 12v wall adapter that will generate a generous amount of current for the LEDs. My question concerns the wall adapter. In the very site that sells it, it admits that the wall adapter is variable and needs to be plugged into a regulator on the breadboard before use. Additionally, some sites seem to sell power supplies that are "regulated" https://www.jameco.com/z/GS06U-4P1J-MEAN-WELL-AC-to-DC-Slim-Line-Regulated-Switching-Wall-Adapter-15-Volts-0-4-Amps_1940707.html.

The solution is simple enough if my Wall Adapter needs regulating:
https://www.canakit.com/1-5-24v-300ma-regulated-power-supply-kit-ck277-uk277.html

So do I regulate my wall adapter or not?
 

Reloadron

Joined Jan 15, 2015
5,138
Most newer wall worts or wall adapters actually use a small SMPS (Switch Mode Power Supply) to derive their output. If using LEDs designed for use with 12 volts then just about any SMPS wall adapter should work fine as long as it provides your needed current. Also most 12 volt LEDs really don't need a well regulated 12 volt power source.

<EDIT> I see Max already addressed it. </EDIT>
 

Thread Starter

clangray

Joined Nov 4, 2018
25
Most newer wall worts or wall adapters actually use a small SMPS (Switch Mode Power Supply) to derive their output. If using LEDs designed for use with 12 volts then just about any SMPS wall adapter should work fine as long as it provides your needed current. Also most 12 volt LEDs really don't need a well regulated 12 volt power source.

<EDIT> I see Max already addressed it. </EDIT>
Just to make sure. The amps/voltage is just fine...the series of 6 IR LEDs pulls about 50ma through the circuit. I am more concerned with safety/fire with using a wall wart. It seems some folks use the wall wart straight into a barrel jack into the breadboard and some use a breadboard voltage regulator like here(below)
https://www.canakit.com/1-5-24v-300ma-regulated-power-supply-kit-ck277-uk277.html

If one can just plug a wall adapter barrel plug into its receptor on a breadboard wouldnt this be easier than a breadboard PS kit?

Under what circumstances would one use this breadboard power supply kit?

Sorry about my dubious nature, just need to vett the issue for safety's sake. Thanks in advance.
 

MaxHeadRoom

Joined Jul 18, 2013
20,028
That appears to be just a regulated supply for maybe a supply such as simple unregulated rectifier bridge supply, a Wall-Wart SMPS offers this already without the need for the extra supply.
Wall-Wart supplies are used with a barrel connector for circuit board supplies all the time.
Max.
 

Thread Starter

clangray

Joined Nov 4, 2018
25
That appears to be just a regulated supply for maybe a supply such as simple unregulated rectifier bridge supply, a Wall-Wart SMPS offers this already without the need for the extra supply.
Wall-Wart supplies are used with a barrel connector for circuit board supplies all the time.
Max.
Thanks for the added info, I feel better proceeding forward.
 

Reloadron

Joined Jan 15, 2015
5,138
Your link, Plug-In Breadboard Regulated Power Supply is a complete fixed or variable power supply, The full wave bridge rectifier and filter capacitors are visible on the board. It takes an AC or DC input:



    • Supply voltage: 9 to 15V DC or 6 to 12V AC adapter (15V DC or 12V AC required for 12V output)
Under what circumstances would one use this breadboard https://www.canakit.com/1-5-24v-300ma-regulated-power-supply-kit-ck277-uk277.html if one can just plug a wall adapter barrell plug into its receptior on a breadbored?
I guess if someone wanted a small low current supply with an adjustable output capability they may have use for it.

Older wall warts and wall warts in general are very safe. The older transformer types offer galvanic isolation from AC mains. You can place a short across most wall warts, the good quality ones, and they do not heat up. I have never seen a wall wart start a fire or melt down. When considering a power source you consider what you need it for and in your case of powering a half dozen LED IR Emitters I would just go with a simple wall wart offering a 12 VDC output. You can break down the wall wart types such as unregulated, a linear regulated transformer type and lastly a regulated SMPS type. Wall wart is merely a generic term. If you have concerns as to safety then fuse whatever you choose with a simple inline fuse. Anyway, for your intended use I would just go with a 12 VDC SMPS type wall wart not that strict regulation is necessary but a decent quality wall wart is inexpensive and perfectly safe.

<EDIT> I see while I typed and fed the dogs Max covered it quite well. :) </EDIT>

Ron
 

ebp

Joined Feb 8, 2018
2,332
If you are only powering the LEDs, then an unregulated supply is likely OK, but it will be necessary to make some measurements. Typically the secondary voltage of a small transformer will be well above nominal with no load or a light load. A wall wart that is nominally 12 volts might well produce 18 V when very lightly loaded. This of course requires a higher resistor value for the LEDs - and possibly higher power rating for the resistor. I would measure the unloaded voltage, calculate the resistors, try the LED string with the resistor and verify the voltage under load. A lower resistance might be required.

The other thing that must be considered with an unregulated ww is variation in your AC line voltage. In many places that isn't much of an issue, but in others it can be.

An LM317 voltage regulator can be used to make a very simple constant current regulator with just a single resistor. You'll find how to do that in the datasheet. An LM317 in the TO-220 package (which can be attached to a heatsink) is around a dollar.

[EDIT] With 20 V in and about 7.2 V across your LEDs, an LM317 delivering 50 mA would dissipate about (20 - 7.2) V x .05 A = 0.64 W. It would run quite warm, so a small heatsink might be desirable though not really necessary if the ambient temperature isn't too high.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,028
Unregulated Wall-Warts usually rely on the rated load in order to bring them down to the stated voltage, the O.C. voltage is much higher.
Max.
 
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