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!

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…

Let’s talk regulators

IMG_20140918_193021As you probably know by now, I have released a few of my “old” circuit boards for sale on Tindie. Actually, they’re all revisions of previous boards I’ve shown off on the blog before. The one board you have not seen revised yet is my AMS1117 3.3&5v fixed voltage regulator board, pictured on the left. I’ve been looking over the design, while also straying away from it looking at other low drop out (LDO) regulators.

Functionality of the original board was not a problem. I still use these boards for prototyping and testing, and also in my final project builds like in my 24/7 powered ESP8266 project. The worst part of the board are the capacitors because they’re so close to everything else on the board including each other. I didn’t leave enough room between the larger capacitors so they’re awkwardly pressed up against each other. It’s so bad that I used hot glue to keep them solid in place because some of the capacitors aren’t sitting flat on the board. This can be easily fixed in the next revision by moving to SMD parts, which has been the plan for all of the boards since I decided to revise them all.

IMG_0767With the drop out voltage of the diode (reverse input voltage protection) and the regulator itself, you’re required to supply at least 7v to get 5v out of it. That’s the same thing as everyone’s favorite LM7805 which has a drop out of 7v, without a protection diode which would add another ~0.7v to the total drop out of your regulator. With that said, I pretty much only use 9v batteries with my AMS1117 board because it meets that minimum input voltage without being too much over. I have the ESP8266 project powered 24/7 so I’m obviously not using batteries but a 9v wall power supply.

spx1117circuit
SPX1117 schematic in Eagle – “Improved Ripple Rejection” circuit from datasheet

Speaking of wall power supplies, it introduces another “issue” if you use one with a voltage regulator. I don’t own a bench power supply or oscilloscope so I can’t get down into the fine details of  better monitored current draw or frequency response. You don’t have problems with frequency response with batteries because they output a solid DC voltage. However, with wall power supplies, the power from the wall is a rectified sine wave which is bound to have ripples in the output. I’ve been considering the change to the SPX1117 regulator which has a circuit in the datasheet to reduce the ripple… but then I wonder how much this actually matters to anyone. For hobbyist projects which is what these boards are made for, it’s really not going to have any major affects to it, as demonstrated in my projects that have worked well with the regulator board for extended periods of time.

I’m not really sure which regulator I’m going to go with. The main reason for looking at the SPX regulator is because they’re more readily available from my go-to suppliers than the AMS regulator. I may even just put the regulator circuit on the boards that would need them, like the ATmega328p breakout board. That’s the biggest motivation for designing these regulator board anyway. In that case, I probably wouldn’t need a regulator that can put out as much current (800mA)… We’ll see! Thanks for reading!

AMS1117 Board Test Results

In my last post, I talked about assembling my two new PCB designs. In this post, I’ll talk about the results of some tests with the AMS1117 dual fixed voltage regulator board.

As I was assembling the board, I had realized that I hadn’t accounted for the voltage drop of the diode. It wouldn’t be an issue, except that  I wrote that the maximum drop out of the AMS1117 is 1.3v on the back of the board. Theoretically, there’s a dropout of 2v with the reverse polarity protection diode in the circuit, which is about the same dropout as the LM7805 voltage regulator. I’m glad I put in the diode though, since I’ve accidentally connected the battery backwards a few times already.

Anyways, I don’t have a variable voltage supply so I built an LM317 variable voltage regulator on a breadboard for this test. The test was to ramp up the voltage to see when the 3.3v and 5v outputs would appear so I can measure the dropout.IMG_20140919_101619

You can find my test notes here. Basically, I found that the total dropout with the diode for the 3.3v regulator to be 1.74v and 1.59v for the 5v regulator. I’d round up the total dropout for both to 1.9v, or 2v to make things easier. I chose the AMS1117 instead of the LM7805 because of the lower dropout, but I forgot about the protection diode. I’m still glad I went with it because it reduces the board size significantly, and the SMD soldering is fun.

Test results for the ATmega328p Breakout Board should be posted soon. It was a pretty basic test, which it passed. Yay.

Thanks for reading!

New PCBs! (AMS1117 regulators & ATmega328p breakout)

I’m excited to finally have my second round of PCBs here! The designs are an AMS1117 regulator board and an ATmega328p breakout. I already have notes to share from soldering one of each to start testing them. The notes in this post are just from assembling them. I will have a separate post that goes into detail about my tests with them.IMG_20140918_193548This is how the boards were designed. They are meant to split apart easily with the tab between them. I got a little excited and went for it without scoring it first, so I destroyed one ATmega328 breakout since the weakest points in that area are the pin pads 2-4. No worries though, I got a few extras in this batch of PCBs, probably because they don’t take up the complete 5x5cm area I have to work with. I tried splitting another board by scoring both sides with a knife and they split cleanly without damage to either design.IMG_20140918_193021This is the AMS1117 board that has two fixed voltage AMS1117 voltage regulators. One produces 5v, the other produces 3.3v. It is a tight squeeze because the capacitor footprint is smaller than the actual capacitors, but it doesn’t seem like it’s an issue. On the back side is a note, written in text that’s a bit too small, that the dropout is 1.3v so you have to supply it with at least 4.6v for 3.3v or at least 6.3v for 5v. I forgot to include the drop of the diode which should be 0.7v, but most applications would probably use a 9v battery as the input to this board. It will be part of the testing, though 1.3v is the maximum dropout so results may vary between the regulators. We’ll see how the tests go.

It was fun placing the SMDs and trying to align them properly. It bugs me when my components end up in some awkward position so I feel the pressure with these small SMDs. I got to solder SMDs back in school where we used a flux pen, solder paste, and a toaster oven. I have none of those things so it’s hand soldering for me.
IMG_20140918_192836This is the ATmega328p breakout board. (The crooked oscillator is bugging me.) I really bumped my head with that terminal block for the power input. The terminal block I used on the board is 3.5mm while I’m sitting here with 5mm (0.2″) terminal blocks, which are the ones found on my Attiny85 board. It’s not a big deal as I can always go and buy them, or I can just solder wires like I did with this one.

The boards have proven to be functional, together no less. Again, full test results will be coming up shortly. Stay tuned! Thanks for reading!

Mailbag: Stocking up for the future!

I put in an order last week at Dipmicro because they were having a sale. Some of the sale items were things that will be used on my second board design so I decided to pick them up now. Here’s what I got:IMG_20140806_155026The next board will be a voltage regulator that has two fixed output voltage levels: 5v and 3.3v. It will be using the AMS1117 voltage regulator. The board will also need a diode for reverse polarity protection on the input and some capacitors to filter the input and output voltages. I’ll have more on this PCB soon.

I also picked up a couple shift registers, an Attiny85, some male-female jumper wires, some right angle headers, some 100K potentiometers, and some small signal diodes. I like to stock up on these kinds of things, just in case…

IMG_20140806_211530~2They included a business card which is something new. They opened a physical store in Niagara Falls, Ontario not too long ago. Too bad I don’t live near there.