To get an efficient 12V to 5V regulator, you can look at the 7805 equivalent modules like the AMSRO1-7805 or the VXO7805, these are switching regulators so they are efficient but noisy so you might want to put them in a metal enclosure (a heat sink as part of the enclosure is a good idea) and put say a 10 uF and 0.1 uF capacitor right next to them, to reduce radiated noise. They are pretty much a drop-in replacement (double check that you have the pinout right though as otherwise you can let the magic silver-grey smoke out.)
You can search for such things on https://www.findchips.com/ - They cost me $2 or so each, not lots more than a regular 7805, and I tend to install those in anything battery-powered as you get ~90% efficiency, which beats the heck out of the ~42% efficiency you get out of a stock 7805 run on 12V! Reminds me to buy a few more. I'm putting some into a couple always-on AC powered devices just to reduce power costs on AC.
Mark
On Thursday, July 9, 2020, 06:36:15 PM PDT, Bob Lunsford via groups.io <nocrud222@...> wrote:
I remember reading in an old spec sheet for a three-terminal regular that the operating voltage of the regulator was three volts. This no doubt depends largely on the design of the regulator but 3-4 volts should be considered operational. Keep in mind that if you use the maximum applied voltage, that means about 30 volts at the operating current needs to be dissipated unnecessarily because of the heat. Applying 12V is not excessive to me, though. Still, however, some kind of heat sink or fins on the three-terminal regulator is to me cheap insurance.
Bob ¡ª KK5R
On Thursday, July 9, 2020, 12:28:59 PM EDT, Evan Hand <elhandjr@...> wrote:
Peter,
Before you go through the trouble of building in the "noise" filter, I would first verify that the noise is coming from the 12 supply.? The best way to do that is to test the noise level on battery power.? You do not need to transmit, so any 12v battery capable of supplying 250 to 300 ma for a short time should do.? I have used a car jumper battery that I have and found little to no difference in the noise level on battery power vs mains supplied through either of my TexPower 13.8volt switching supplies. The noise is coming from the antenna in my neighborhood caused by QRM and high QRN noise levels on the air in general.
With the above understanding, I will make some suggestions for R2 to reduce the power dissipation of the 7805 regulator.? ?That does depend on the total current that you will need from the regulator, and THAT depends on what you have planned to add onto the rig that will need 5 volts.? If you add up the power requirements of all of the devices on the stock rigs, the total current is much less than 200ma, more like 120 ma (approximate, as I have not done all of the spec sheet validations? I did look up the stock version 6 2.8" display and that has a max of 80ma).? Then you have the minimum voltage that the 7805 needs to regulate to 5 volts.? I use 3 volts to get some safety margin.? That means you need to supply 5 + 3 = 8volts minimum at maximum current.? If the input voltage is truly 12 volts, and you want 8 volts to the regulator minimum at 200ma, and you need a 4volt drop at 200 ma, then 4/.2=20ohms.? That resistor will need to dissipate 4*0.2 = 0.8 watts.? All of these calculations are DC values, so the simple E=IR and P=EI and the transforms work.
For my rigs, I am adding second Nanos, larger displays with built-in GUI processors, and signal processors, so I have upped the max current to <1 amp (the maximum that the 7805 provided by HFSignals can regulate) and added other safety margins to get 4 ohms at 4 watts.? Were I to do it again, I would have added a second 7805 to supply the auxiliary equipment and not modified the Raduino board.
In general, the stock setup works well, and no changes are needed.? Adding a heatsink to the regulator can help if you are going to operate in high ambient temperatures.??
The other comment that I would make is that if you find you have RF noise from the power supply, then you will need to add capacitors to filter the higher frequency.? Something like a 0.1 to 0.01 uF ceramic disc.? The 470uF will not filter higher frequency stuff.? There is too high of internal resistance at RF in electrolytic capacitors.? You may also be better off to add an RF choke instead of the resistor.? I will let someone more knowledgable on that subject to make a true recommendation.
The above are my thoughts and should be verified before you take action on them.? I do make mistakes at times.
73
Evan
AC9TU
