Voltage through controllers

BundyRoy

Dedicated elf
I've noticed that when powering a controller circuit board it seems to be either 5V or 7-35V. Sometimes you even have to change a dip switch or pin connectors when using the 5V. Why is this. One setting seems to handle 5V only and the other setting handles a large range of volts, ie. anything greater than 5V within the range that we commonly use. I guess that maybe the 5V setting handles less than 5V but there are no lights that operate on less than 5V.

I figured there must be a reason and there was only one way to find to find out. Thanks.

Devo

Apprentice elf
Community project designer
The reason for this is because most voltage regulators/converters only regulate properly at a certain threshold (also called dropout) voltage above the rated voltage output. For example, most 5v regulators have a dropout voltage of 1.5-2v, meaning that you have to input at least 6.5-7v before it will regulate the output voltage and current properly. So that's why on most controllers you have to either input above that threshold voltage (ie ~7-30v) or just run the board straight off a 5v input directly without any onboard regulation.

Pixels! I need more pixels!
The board requires 5 volts to run its own circuitry.

The board also has a regulator on it which will take varied voltages and bring it down to 5 volts.

So you can power the board directly with 5 volts or connect the regulator (via a jumper) and the regulator will sort out the voltage.

Does that make sense?

algerdes

Al Gerdes
I do believe, and hope to be corrected if I have been misled, that most circuit boards use 5v for the control circuits. If you are feeding the board a properly regulated 5 volts for output to the lights, then you can set the board's control circuits to use that 5v directly. If you are using more than 5 volts to power the lights, the control board must switch in a voltage regulating circuit to bring down to 5 volts for use with the onboard control chips.

Note that most items I have read say to use a "well regulated 5v supply".

algerdes

Al Gerdes
Thanks Devo,
I had forgotten about the extra voltage needed to make the regulator circuit to kick in.

BundyRoy

Dedicated elf
Thanks. I figured it would have something to do with ratings on regulators etc. Didn't realise the board circuitry ran on 5V though.

So a regulator can transform say 7.5V back to 5V and the same regulator can transform 35V back to 5V.

BundyRoy

Dedicated elf
Also why was 5V chosen as the voltage to run the board. Cheaper, easier for parts, just because that's the way it's always been done?

Devo

Apprentice elf
Community project designer
Most logic circuitry runs off either 5v or 3.3v. 5v is still a very common running voltage for most logic ICs, and this stems back to the early days. Today however a lot of new logic runs off lower voltages such as 3.3v or even down to as low as 1.8v (like your PC CPU.) The lower the voltage the more efficient it is in terms of power draw.

algerdes

Al Gerdes
On the computer side, and therefore on most electronic based systems, the lower the voltage you can use, the less heat generated during operation. When pushing so many changes through a transistor, it tends to get warm anyway. We don't need a double whammy.

BundyRoy

Dedicated elf
Was thinking about the extra voltage required for the regulator to kick in. Wouldn't this mean you could do it with one circuit. You put in 5V, the regulator doesn't kick in, yous still have 5V. Put in 12V, regulator kicks in, you have 5V. Or is it the case that if the regulator doesn't kick in you have no circuit and 0V.