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.
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 power 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 just 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)