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…

Atmega328p Breakout PRO

The Atmega328p Breakout Board has been out of stock for a while. I have half of the new components in hand, and the PCBs have been shipped and are on their way. The rest of the components will be ordered in the next couple of days and, if it’s like the last time I ordered, it will arrive the next day. Friday is Good Friday so I have to keep that in mind, and hope that everything comes in by then. I’ve made the decision that I will no longer sell unassembled kits so I hope I can use this long weekend to put them together so I have a decent stock ready for the next week.

Anyways, while I’ve been waiting for the new batch, I’ve been working on something else…

draft1To the right is the first draft of the Atmega328p Breakout Pro. The current base version will likely drop the ISP header. The new Pro version will sport the ISP header, in addition to a voltage regulator circuit. As I talked about in the last post about voltage regulators, I’ve been using my AMS1117 voltage regulator boards with my Atmega328p Breakouts in my own projects. With the built in regulator on this Pro version, I won’t need that extra board. The regulator I’ll be using this time is the NCP1117.

I believe the NCP1117 is the same regulator as the one on the Uno, or at least similar. It can output a fixed 5v at 800mA, even though at 800mA it’s best to just use another supply if you’re driving things that need that much current. When I was learning about PLCs, I was taught to separate the power supplies between the control unit (the PLC) and the actual peripherals (sensors, indicator lamps, etc). I don’t see why that lesson can’t be applied to Arduinos, even if they draw less current than a PLC.

I’ve added in the reverse input voltage protection diode so the total drop out is roughly 2v, just like on the Arduino. You’ll need to supply it at least 7v to get the 5v, and I’d limit the input to 12v tops just because of heat dissipation.

I’ve been trying to find out if it’s acceptable to have an external voltage applied on the output of the regulator. I want to be able to apply an external supply to Vcc (the output of the regulator, and the input power supply of the microcontroller). That way, you could use a battery or supply that’s already in the operating voltage range of the Atmega328p (1.8-5.5v). I’ve been looking at some Arduino and Adafruit schematics and it looks like you can, if you consider USB Vcc as an external 5v supply. They have it connected to the same 5v net as the output of the regulator (although the Adafruit schematics use a different regulator). I’ll keep researching and probably put together a prototype demo circuit and see what happens.

That’s it for now! Thanks for reading and I hope you’ll stop by my Tindie store and pick up some of my Atmega328p Breakout Boards when they’re back in stock!

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!

Tutorial: LM317 Variable Voltage Regulator

I noticed a couple people landed on the blog because they were searching for information on the LM317 voltage regulator. I figured I should do a tutorial on it and hopefully they’ll come back to see it.

Here are some of the key features listed on the datasheet: Max output current is 1.5A; Adjustable output voltage between 1.2V and 37V; Current limiting and thermal shutdown protection.

When you’re connecting the circuit, take careful note of the pins on the regulator. From left to right: Pin 1 is Adjust, Pin 2 is Vout, and Pin 3 is Vin. This is important to remember as the circuit diagram has a different order when you read the diagram from left to right.

The circuit in the datasheet calls for capacitors but I didn’t include them for this basic demonstration. They’re used to smoothen out voltage spikes and improve the transient response. The datasheet calls for 0.1uF and 1uF at Vin and Vout, respectively. If you’re using electrolytic capacitors, make sure that the polarity is correct. The negative side is marked with a white stripe. That side of the capacitor should be grounded while the other side goes to Vin or Vout. I’ve read that ceramic capacitors have a better effect on the transient response so feel free to use them if you have them. They’re not polarized so you don’t have to worry about which way they’re connected.

I connected the circuit shown in the datasheet, minus the capacitors, and supplied it with my unregulated 9v DC power supply which actually supplies around 12v with no load.

IMG_0850The minimum output voltage checks out at 1.2v.IMG_0849This was the maximum voltage I could get out of the regulator’s output. As I said in the power supply tutorial, it’s never a good idea to ask more from your power supply than it’s rated for. When you’re using the LM317 regulator, chose a power supply that supplies a higher voltage than what you’ll actually need.IMG_0852Here’s the regulator circuit adjusted to drive a yellow LED. All you need to do is turn the potentiometer and read the output on a multimeter until you get your desired voltage.

If you don’t want to use a potentiometer, you can calculate your R2 once you have chosen an R1 and you know your desired output voltage, Vout. I thought it would be neater to take a picture of my notes rather than try to type out those equations…

IMG_0856So if we were to replace the potentiometer with 1.5kΩ, we should get 9v…

IMG_0854That’s so satisfying.

I hope this helps out those looking for information on the LM317 regulator.