Guru
Joined: 21/06/2018
Location: AustraliaPosts: 1156
| Posted: 03:27pm 11 Jun 2024 |
Spent some time playing with the 12V to 5V regulators, switching type versus linear.
The Nano has an 800mA regulator on board but don't think you can put 12V in and get much useable current out of it. The Nano LCD display draws ~60mA probably 59 for the backlight and 1mA for the logic. So I got a Nano module put 12V on Vin and connected the LCD between the 5V and ground, after a couple of minutes the tab of the regulator was over 70 degrees from a starting point of 17 degrees for ~ 0.42W dissipated.
So my theory of how to drive the Nano LCD backlight from the onboard 12 to 5V regulator is a non starter.
Next I got a 4pin KA78R05 regulator with an enable, I put a 1K between the enable and ground so the regulator is off. Next I put an 8V2 Zener from the enable to the 12V input, now when the input is ~ 1V higher than the zener voltage the regulator snaps on. When the input is ~ 9.1V the regulator puts out a few millivolts, but when I increase the voltage to 9.2V the regulator snaps on with 5V output again. Note the 1K is the correct value calculated from the data sheet, the 4K7 I mentioned a few posts ago was more of a guess despite that it actually did work for that part.
The new result when I run an LCD from the larger plastic pack KA78R05 from 12V with the LCD on after a similar amount of time is much better. After a few minutes the input pin close to the regulator case achieved a temperature of 40 degrees from a 17 degree start. The heat of the part was a bit over lukewarm for the same 0.42W dissipated.
Video clip shows a 12V input DVM, output 5V DVM, and when I toggle the supply voltage from 9.2V to 9.1V and back again how the 5V snaps off. It shows what will happen as the normal 12V input collapses and passes the 9.1V mark. I will mark up a schematic and proposed board mod to fit the linear regulator. Sorry the video is 90 degrees rotated but I can't be bothered connecting it all up & re shooting it again, video is here. Although I didn't show a scope image of the 5V falling it just drops like a rock.
I think using the linear regulator part instead of the 12-5 noisy switching regulator, and the clean 5V collapse versus the slow noisy droop is a great improvement. I will include some of these regulator with each shipment of boards I send out.
Edited 2024-06-12 11:58 by wiseguy