I have finished my "rpm meter" and have been testing it. I'm very happy with how it all works, so now I'd like to solder it up into a permanent circuit including a standalone arduino (ATMEGA328P-PU) much like this guy has done. To do this then, I have my adafruit boards, and will be following the arduino breadboard tutorial. I have ordered everything I need for that from Tayda.
While waiting for my parts to arrive, I was doing a lot of googling and reading about making your own standalone arduino. I came across a youtube video of someone building the breadboard arduino circuit. The commenters said that using the 7805 voltage regulator with a 12V supply will cause the voltage regulator to get very hot, which is something I didn't know, but quite important for me as I want to use a 12V power supply (well, I don't really want to...it's been forced upon me). So my understanding now is that these kind of breadboard arduino builds are best run with a power supply which is 5V or as close to that as possible so as not to overheat the 7805 volatge regulator.
The place where my standalone arduino (and circuit) will be mounted is an enclosed space - a wooden rectangular box which has holes on one side for airflow, and a computer fan built in on the other side (which runs at 7000 rpm) to generate the airflow. There is also a small DC motor in that space whose rpm I am tracking, and that's why the fan is there in the first place. The standalone arduino will be mounted right next to the fan (basically because there is nowhere else that I can place it), so that's one good thing. But my questions are:
Is a fan like this good enough to keep the voltage regulator cool, or do I definitely also need a large heatsink for the 7805 as well?
I came across an alternative voltage regulor in my google travels, the DE-SW050. The product page suggests that it is good for "any application where a linear or LDO regulator is dissipating too much heat or a large heatsink is undesirable ".Would this be a better choice for me to use instead of the 7805 if I want to use a 12V supply or will I still have heats problems with this regulator too due to the 12V supply?
If I it is possible to use the DE-SW050 instead of the 7805, is it just a simple matter of building the whole circuit exactly as the breadboard arduino tutorial suggests and just substituting the DE-SW050 for the 7805? The DE-SW050 datasheet says that it is "pin-compatible with the common 78XX family of linear voltage regulators". Also, "They have integrated decoupling capacitors, so external capacitors are not generally necessary". Just thought I would double-check all that with the gurus here first!
Apologies for the long post. Hopefully someone out there has some ideas, or suggestions. There are undoubtedly many things I have not though about!
The commenters said that using the 7805 voltage regulator with a 12V supply will cause the voltage regulator to get very hot, which is something I didn't know
This would be true depending the amount of current the circuit will drain.I have some small boards using the 7805 and atmega328 and the regulator does not get hot since it is just powering the avr and some one-wire sensors.
The commenters said that using the 7805 voltage regulator with a 12V supply will cause the voltage regulator to get very hot, which is something I didn't know,
Sounds like a warning without an explanation.
As the other guys indicate, the heat dissipation also depends upon the load current,
and is given by Pd = Vdrop * Iload = (12V - 5V) * Iload = 7V * Iload. And Pd should
be no more than a couple of watts to prevent overheating. The good thing about
7805 TO-220 v.regs is you can use a heatsink with them.
For Vin = 12V, you definitely do NOT want to go with smaller surface-mount v.regs,
ie SOT-223 or SOT-23, as used on many Arduino boards. This matter comes up so
often, I wrote up a page to cover some of the issues, http://www.ot-hobbies.com/resource/heat-diss.htm
I use these for power supplies got them when Texas Instruments were giving away samples.
PTN78020WAS 6-A Wide-Input Voltage Adjustable Switching Regulator.
They only need a filter cap on the out put and a suitable transformer. I just plug them into my fixed voltage desk power supply. They are only 3/4 x 1.5 inches and work well.
oric_dan:
For Vin = 12V, you definitely do NOT want to go with smaller surface-mount v.regs, ie SOT-223 or SOT-23, as used on many Arduino boards. This matter comes up so often, I wrote up a page to cover some of the issues, http://www.ot-hobbies.com/resource/heat-diss.htm
That's a helpful page, however it appears to contradict your own advice in the above paragraph. Your table shows quite clearly that a SOT-223 or even SOT-23 chip is adequate at load currents of 50mA @ 12V input. A standalone atmega328p clocked at 16MHz takes only 10mA. So if you are not powering much else from the +5V line, and not connecting heavy loads to the Arduino output pins, then those small regulators are more than adequate.
LCD backlights can take a lot of power, sometimes as much as 100mA. To keep the regulator power dissipation down, I usually drive them from the unregulated supply via a series resistor.
That's a helpful page, however it appears to contradict your own advice in the above paragraph. Your table shows quite clearly that a SOT-223 or even SOT-23 chip is adequate at load currents of 50mA @ 12V input.
Thanks for pointing that out, dc42 [maybe one day I'll find out if you have a name too ;-)], and also
for perusing the v.reg heating page.
Personally, I don't think 50mA is a very useful value, all in all, especially when people advertise
"1A" regulators, but in my previous post I was mainly trying to point out to OP [Candice] that
7805 TO-220 can actually push a decent current for Vin=12V without overheating, and SOT-223/23
will be far worse.
Ref,
The commenters said that using the 7805 voltage regulator with a 12V supply will cause the voltage regulator to get very hot, which is something I didn't know, but quite important for me as I want to use a 12V power supply (well, I don't really want to...it's been forced upon me).