External power supply for LEDs?

I am using WS2803 LED driver. I also got bunch of other stuff in my circuit, including standard Hitachi HD44780 LCD module. Now, when I turn on all 18 LEDs (I'm using 1.3k resistor on IREF pin), they all work, but suddenly I can't read anything on LCD display - backlight is still on, there's just no text. So, when all LEDs are off, display works just fine. But, as soon as I start lighting LEDs up one by one, I can read less and less on display until I can't read anything anymore. All of this suggests that LEDs cause significant voltage drop so I should use external power supply for LEDs. Questions:

1) Am I right? 2) If I am - well I don't actually want external supply, I'd like to use voltage regulator or something else, as long as I can power everything via USB, so I hope somebody can suggest me some solution.

It certainly looks like you are using too much current. Do you have a meter to measure the 5v supply?

Weedpharma

weedpharma: It certainly looks like you are using too much current. Do you have a meter to measure the 5v supply?

Weedpharma

I do. What do I need to measure?

Find the 5v pin on your board and measure between that and Gnd. See if the voltage drops from 5v when you turn on more LEDs.

Weedpharma

weedpharma:
Find the 5v pin on your board and measure between that and Gnd. See if the voltage drops from 5v when you turn on more LEDs.

Weedpharma

Hm. It’s 4.98V with all LEDs off, and 4.75 with all LEDs on.

Seems to me that you need external power.

Weedpharma

weedpharma: Seems to me that you need external power.

Weedpharma

Yes, I was thinking about using LM317 - I'm just not sure should I power only LEDs using that regulator, or WS2803 as well.

What is your power source? A switching regulator may be more efficient if drawing 1/2A or more.

I would use it for the WS2803 as well.

Weedpharma

weedpharma: What is your power source? A switching regulator may be more efficient if drawing 1/2A or more.

I would use it for the WS2803 as well.

Weedpharma

Power source is USB. Well if all 18 LEDs are on, and each uses 20mA, that gives me 360mA, so LM317 should handle it fine. I'm not too familiar with switching vs. linear regulator differences.

Edit:

I see LM317 requires 2-3V of drop-out voltage, so that's not an option. TC1262 (5V) seems very good for what I want.

TC1262 is 6.5V input absolute maximum. An LM1117 is the more typical choice. Make sure you use input and output capacitors as recommended by the datasheet with any LDO regulator like these.

With a linear regulator (LM317, TC1262, LM1117 ... or any circuit that doesn't include an inductor) you will burn off (Vin - Vout) * A as heat. So if you're regulating 10V down to 5V at 1 of current with a linear regulator then you're only 50% efficient and the chip is acting like a 5W heater (which is hot for a little chip).

A switching regulator is around 95% efficient regardless of the input or output voltage. If you jump on eBay and search for "LM2596" you'll find many sellers of inexpensive, variable voltage regulator boards that cost about $1.50.

Chagrin: TC1262 is 6.5V input absolute maximum.

Yes and? I was going to give it a bit less than 5V (USB). And I'll be happy with anything from 3.6V to 5V on output, with at least 400mA current. I'm trying to find ideal solution for this for the past few hours with no luck.

Chagrin: A switching regulator is around 95% efficient regardless of the input or output voltage. If you jump on eBay and search for "LM2596" you'll find many sellers of inexpensive, variable voltage regulator boards that cost about $1.50.

Pretty sure those are fake crap ICs.

Remember that USB from the host computer can only supply 500mA total.

kustom: Power source is USB. Well if all 18 LEDs are on, and each uses 20mA, that gives me 360mA, so LM317 should handle it fine. I'm not too familiar with switching vs. linear regulator differences.

Edit:

I see LM317 requires 2-3V of drop-out voltage, so that's not an option. TC1262 (5V) seems very good for what I want.

If your power source is USB, you don't need external power UNLESS a you have too much current. This is obviously what you have to drop the voltage so much.

You need external power source such as a plug pack to drive the non Arduino parts. Using a linear regulator is not as efficient as a switching regulator.

http://uk.rs-online.com/web/p/switching-regulators/6664379/

Weedpharma

kustom:

A switching regulator is around 95% efficient regardless of the input or output voltage. If you jump on eBay and search for "LM2596" you'll find many sellers of inexpensive, variable voltage regulator boards that cost about $1.50.

Pretty sure those are fake crap ICs.

But they work.

weedpharma: If your power source is USB, you don't need external power UNLESS a you have too much current.

I obviously do, since I'm also using 4 4067 multiplexers, 2 MCP23017 expanders, LCD screen and 10 encoders. Problem part here are LEDs obviously. I tried to power them using additional USB cable and it worked, but I was hoping I could simply use some kind of current-amplifier transistor or something similiar, which wouldn't result in requiring additional supply (that is, I'm hoping to use one USB cable only, but it's not the end of the world if I can't).

EDIT:

I also tried to implement "matrix" of sort, that is, I tried using setup in code where only 3 LEDs are allowed to be on at the same time, while others are off. I just can't get it to work without flickering (tried using SPI, shiftOut, polled checking using millis(), interrupts etc, nothing worked reliably).

The USB from whatever source is limited by the supplying device. It is not just a function of the Arduino that is limiting the current.

Weedpharma