24V Derivation

Hi:

I have a 24V power supply and I need to derivate 5V to operate and arduino uno and 6V to operate a high torque servo. How could this be done whithout risking the arduino?

Use a voltage divider to take the 24V (assuming DC) to 12V for your Arduino and divide again for your servo.

http://en.wikipedia.org/wiki/Voltage_divider

Google OKI 5V regulator and LM317 adjustable regulator. Also, you could uze a 6V lantern battery from a H/W store for the relay.

Are you at all concerned about efficiency? A linear regulator would give you a cheap solution but all the power corresponding to the voltage drop would be lost as heat - going from 24V to 5V means you’d only have a 20% efficiency. If you want something more efficient, look for a buck converter.

If you use a linear regulator as was suggested above... You will need a rather large heatsink as the power Wasted is the load current multiplied by the voltage drop across the linear device... Not really a great idea unless your load current's are very low. .1 A X (24 - 6) is 1.8 watts and 5 Led's can easily draw .1A or 100 mA. A switching supply (regulator) is a better choice as the loss is the efficiency X the load [u]power[/u] IE a 100 mA load @ 6V is .6W and @ 80% efficiency it would be .8(80% Eff) X .6 watts (load ) or .48W (loss) vs 2.4 + .6 (load) or 3 watts loss of energy as heat Vs 1.48 Watts for the linear regulator and 1.8/2.4 = a 25% greater efficiency. I tend to think of switchers as Power converters rather than Voltage converters. The immediate effect for a very light load @ 100 mA seems a small savings But at higher load currents... EX: 1A X (24V - 6V) is 18 watts of power lost as heat in the linear device but the switcher will dissipate : (1A X 6V ) X .8 [Eff} or 4.8W and where the linear device will dissipate 24 watts of power and 24 watts/4.8watts is a great deal less wasted energy.. a 5X decrease in wasted power... However this is Not to say that linears are bad... A Low dropout regulator does a nice job of removing switcher noise with a much smaller footprint than a Pi section filter. It is a good idea to use a small linear behind a switcher at low current for..? Measurements or Audio applications...... There is a Lot of voltage gain in a linear Reg and as long as the I/O differential is [u]just[/u] great enough to prevent the device from "Dropping Out" or failing to regulate they can be a useful tool... but when improperly used a real headache

FYI, “buck” converter is a DC -to-DC converter which could be a hockey puck sized module.

raschemmel: FYI, "buck" converter is a DC -to-DC converter which could be a hockey puck sized module.

.. or it could be a couple of millimeters across, depending what you need it for.

Very Small too, A 2A continuous duty buck mode CV device that commonly sells for 2 or 3 dollars is 20 X 42 X 12 mm. The CV-CC modules at the same current are about twice the size and sell for less than 5 dollars… Both in single quantities…
A 25 watt heat sink is frequently more money… W/O any parts.
The first one I mentioned is one I use frequently as a pre-regulator for the discarded printer power supply power modules I find and or buy from the local “Thrift” stores… A 30V .7A HP Printer supply is 21 watts of power, and here in the US already UL approved… safe…
This is for me 5V @ 4A output or 7.5V @ 2.5A, An Ideal input voltage for an Arduino board as the voltage (7.5V) is Ideal for the AMS1117-5.0 regulator on any of the Uno, Mega and Leonardo boards I use… When I designed my own… back when I worked for a living were even smaller… An MCP16301 will produce 500 mA from a 16.5 V input and is in an SOT-23-5 case… I use one of them to support 2 Sure Electronics 3208 scrolling displays that use the Holtek HT1632 IC with 4, 8 X 8 5mm red matrix LED displays Each…

Doc

This is for me 5V @ 4A output or 7.5V @ 2.5A,

Where is the information to purchase these ? (link to vendor)

So, what would be the best idea to avoid overheating? (since the circuit is going to be inside a cardboard structure)

Basic buck converters found on Ebay are capable of 2A max W/O a heat sink 3A with a heatsink and this will require a piece of copper soldered or firmly clamped (with some heatsink goo too) to the board under the LM2596 and mounted to a 10 X 10 X 15cm or 4 X 4 inch piece of .060 thick piece of aluminum for aheatsink if you require 100% duty cycle… I’d recommend using an L shaped bracket fabbed from 2 mm aluminium and a 2 mm (I don’t know which measurement units you prefer and the “Imperial” measurements are most familiar to me) so a .060 thick 1/2 by 1" bracket with a 6/32 screw mounted to a 4 X 4" .o60 or 1.5 mm is my thought… You will also require a spacer under the device as the connecting wires are PTH type, this to prevent the other pads from accidental contact with the rest of the heatsink… and I use multiple buck converters… the trick is to divide the loads… Think of the primary power source as a high voltage, low current source and the wiring becomes simple. I typed ion the Google search box “Ebay buck converters” and the first or second choice was this… which is identical to that I described in my last forum post on this subject…
http://www.ebay.com/itm/DC-Buck-Adapter-4-5-35V-3-33-5V-Buck-Voltage-Adjustable-Converter-/371039757167?pt=LH_DefaultDomain_0&hash=item5663b1636f
read the description at the bottom of the page… 2A, needs a heat sink for 3A the price was $1.25 on a bid site,

(above courtesy of Docedison)