NCP1117 Board Load Test (Part 2)

In my last post, I tested my NCP1117 5v voltage regulator board with a couple of power resistors. In those tests, I used a wall plug rated at 9v 1A. Since then, I received a new variable power supply which I used to see how different voltages and currents would affect the regulator board.
IMG_20150704_181821For these tests, I stuck with the 5-ohm resistor. I set up the power supply to 9v and “unlimited” current so that the board would draw whatever it wanted. It drew roughly 890mA, read at both the input and output of the board. (The multimeter is measuring the output current.) Unlike the previous experiments, the regulator was able to stay steady for the three or so minutes I left it going. Even though it was able to stay on, the board becomes too hot to handle with bare hands. The current seemed to hit a ceiling at 890mA. Going any higher than 9.5v would cause the regulator to quickly hit its thermal limit and the current would start dropping rapidly. I suspect the wall power supply is slightly higher than 9v printed on it which is why it did the same in my tests with that.


 

Calculations

To calculate the power dissipation that the regulator is dealing with:

Power (P) = Voltage (V) * Current (I)

P = (9v – 5v) * 0.890A

P = 3.560W

From the datasheet, the thermal resistors junction-to-ambient, RθJA, and junction-to-case, RθJC, is 67°C/W and 6°C/W, respectively. Together, it’s 73°C/W, which can tell us how hot the regulator should get:

73°C/W * 3.560W = 259.88°C

Yeah… It needs a heatsink, though the current design doesn’t really allow for a proper one that screws into the circuit board.


I’ve used a similar board that uses the AMS1117 regulator on many projects that were running 24/7 for months. I noticed that the regulator did get very warm but I wouldn’t really call it alarmingly hot as this board was during these tests. I didn’t have the bench power supply by then and I didn’t do any current measurements (doh!), but I can estimate that none of those projects ever pulled more than 200mA from the regulator board. They’ll still be good for those types of projects where I can’t get an already regulated wall power supply. However, I was also using them for prototyping but, now that I have the variable bench power supply, I won’t be using them for that anymore.

I hope these experiments were interesting to you. Thanks for reading!

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NCP1117 Board Load Test (Part 1)

I’ve always wanted to push my voltage regulator board to its limits. The easiest way I figure is to get some low value power resistors to draw “high” amounts of current from the regulator board. I happened to pass by a local electronics supplies store today so I picked up a couple of power resistors, as well as some test leads and a flush wire cutter.

As a side note, I was actually looking for some test leads that have that wire hook thing but they didn’t have any that I liked. I didn’t own any test cables so I’m glad I picked up these alligator-to-alligator test cables. They were an impulse buy on the way to the cash register, where the cashier commented that he personally liked them. They are actually quite nice, though I find them a bit slippery when trying to squeeze open the clips.

Anyways, lets look at how the test went.IMG_20150628_163532 (1)It was a pretty simple setup, especially with the help of my new test leads. I connected the resistor between the +5v and ground output terminals of the regulator board. I had my multimeter in series with the resistor to measure the current. I used a 9v power supply to power the board.

One of the resistors is a 5-ohm 22-watt resistor. It pulled 880mA from the board. The other resistor, which is connected in the picture above, is a 6.8-ohm 5-watt resistor. It pulled 650mA from the board. Both tests caused the thermal overload protection to kick in. In under 15 seconds with both loads, I could hear a buzzing noise coming from the board and see that the current was dropping. The current dropped rapidly to about 350mA where it slowed its pace dropping down, about a mA per second. I didn’t want to leave it for too long so I pulled the plug around this point.

Blowing on the board to attempt to cool it off brought the current back up. I always thought that the thermal overload protection would act like a switch where you’d get no current at all from it, but it looks as though it doesn’t work quite like that.

Linear voltage regulators can be trickier than they seem, at least if you plan on pulling good amounts of current from one. It’s a good idea to expect that your linear regulator will get hot (that’s how they work anyway, it’s sometimes hard to appreciate it with low current projects producing negligible heat) so consider heat sinks and ventilation.


To update those who actually follow along with new posts, I got a job earlier this month (not electronics related, unfortunately). While I don’t have as much time as I did before to work on my projects, the income does allow me to buy more things for my experiments. Coming in next week is a new bench power supply which should make this load test experiment more interesting with different input voltages and current readings from the source power supply. I’m excited.

I also updated my Atmega328p Breakout Board and am waiting for those PCBs.

I hope I can start posting more again as I adjust to things. Stay tuned and thanks for reading!

Updating the regulator

I don’t have a bench power supply so I rely on wall plugs that already regulate the voltage level, sometimes combining it with a regulator circuit/IC to drop it even further. In the beginning, I used to whip up a classic 7805 circuit on a breadboard. These days, I’ve been using a low drop out regulator circuit on a custom PCB. I’ve been using my AMS1117 regulator board for a long time now in projects and prototype testing on a regular basis. It’s clunky and one of my first PCB projects ever. It’s about time it got an update.

IMG_0001It’s been a design I was sitting on for a while. It uses all surface mount components, which I picked up in my last Digikey order and had laying around for a while.

IMG_0002Instead of the AMS1117 regulator, the new board uses an NCP1117 regulator, although the actual IC says RBK117 for some reason. My initial test impressed me as I got a perfect 5.00v on my multimeter. The AMS1117 regulator would usually measure to be +-20mV from 5v. It may end up varying with age but in any case I’m happy that it works. I dropped the 3.3v regulator since I never really used it, except for in the ESP8266 project.

I’m very excited to start using this smaller, neater looking board regularly. I still have a bunch of those bulking AMS1117 boards so I’m not really sure what to do with them now…