I have a 12v 1amp power supply which i step down with a 5v 2a voltage regulator. It is used to power 20 LED's each drawing a maximum of 80ma, giving a total draw of 1.6a. The lights are controlled by an Arduino Nano.
When I turn it on, the voltage regulator outputs ~5v, but after some time (20-30 seconds) the colors in the LED's slowly changes for no reason and the voltage drops to ~3.2 volts. I would expect the power supply to deliver 12watts @ 12v, regulated to 5v it should be (12watt/5v) 2.4amps, right?
Can the voltage drop be caused by overheating in the regulator (it is hot, but still touchable for a short period) or is the power supply being overloaded? Or may it be caused by a third factor I have not thought about?
There is also the problem that your 12V 1A power supply is going to be very unhappy if you plan to draw more than 1A from it, certainly dont plan to draw 1.6A from it.
You seem to be confusing the difference between linear voltage regulators and switched mode converters.
So, you have a 1A supply and want to draw 1,6A?
And a linear regulator that needs to convert the rest (12,8W!!!) to heat?
And you're surprised
And you use Neopixels, not just normal leds. Aka, devil is in the details. Give us schematics, code, type details etc and we can give you useful answers and tips. If you don't, it's just a wild guess.
Surprised? Maybe, sort of, not really.. Just learning by doing, and TIL that a linear voltage regulator will not work for the application I wanted. Measure once cut twice!
I'll just drop the 12v adapter and take the 5v PSU from my RBPi for testing and order an extra 5v adapter for the final assembly. Just had the 12v adapter and a 5v regulator and though: That might work.. Well.. It didn't!
The incoming DC is chopped into high frequency squarewave, fed into an output filter to make 5V.
As load is increased, the output squarewave is increased in pulsewidth to keep the output at 5V.
The high frequency keeps the components small, the ripple low.
Danois90:
Surprised? Maybe, sort of, not really.. Just learning by doing, and TIL that a linear voltage regulator will not work for the application I wanted. Measure once cut twice!
Modern switching regulator is the way to go.
Linear will work if you select the correct regulator and put a decent heatsink on it.
When I turn it on, the voltage regulator outputs ~5v, but after some time (20-30 seconds) the colors in the LED's slowly changes for no reason and the voltage drops to ~3.2 volts.
What are your LEDs, it sounds like you are putting 5V across standard LEDs that drop 1.6V.
The colour change is due to them slowly burning out, the 3.2V is due to the increased current they draw as they die.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
You description does not tell use the type of LED or if you are using current limiting resistor.
Have you put bypass capacitor around the 7805 as per the datasheet?
How is the Arduino Nano switching the "LEDs" ON/OFF?
I've figured out that the switching buck converter would have been what I needed - thank's for the tip on that! But I do not have such converter and I will not get my Christmas light done in time if I should order one for the project. Now I have taken a power adapter from my RbPi, it is rated at 2A @ 5.1V, and I have measured it to 5.3V. This is in the green area but I have put in the before mentioned regulator which gives me a nice 4.25V which is will ensure my LED's not burning out too fast - this works very well! The regulator only has to dissipate a maximum of 1.6 watt and it does only get slightly warm and nowhere near as hot as before. Nice!
@TomGeorge: The LED's are SK6812 SMD5050 rated at 3.5-5.5V (aka. NeoPixels). They did not burn out at all, they are pretty rugged as long as they do not get too much heat during soldering! I have placed a 1000uF capacitor on the regulator's output. The LED's are soldered into 2 strips (2x10), each LED has a 50Ohm resistor on VDD and the data signals each have a 330Ohm resistor attached as recommended. They are controlled using the AdaFruit NeoPixel library and other than that there's not much other to it
Thanks for you help, guys! I learned a usefull lesson about linear voltage regulators and how (not) to use them
Now I have taken a power adapter from my RbPi, it is rated at 2A @ 5.1V, and I have measured it to 5.3V. This is in the green area but I have put in the before mentioned regulator which gives me a nice 4.25V which is will ensure my LED's not burning out too fast - this works very well!
So you have 5.3V feeding the 5V 7805?
The reason you are getting 4.25V out is because 5V input is not enough to give you 5V output that is regulated.
In fact you nay find the 7805 will start to get hot.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can you tell us your electronics, programming, Arduino, hardware experience?
@TomGeorge: The 78S05 will be removed for the final assembly but the LED's are too bright to look at whilst programming the arduino. Each LED has a ~50 ohm resistor attached and with a source voltage just shy of 5.3 it will be a perfect match. I've been programming computers for ~25 years, electronics and arduino for some years
