Electronics > Projects, Designs, and Technical Stuff

How do you tell what "type" of power a DC power supply is?

<< < (4/8) > >>

TimFox:
Reading the label, it appears to be a constant-current power supply for 2.5 A (2500 mA), with a compliance (maximum voltage across load) of 24 V.  However, I don't think that is correct:  instead it is probably a constant-voltage supply ("CV") at 24 VDC, with a maximum current of 2.5 A.  A switch-mode constant-current supply is great for driving LEDs in series without extra loss from a series resistor, but it looks like that strip includes SMD resistors.

John B:

--- Quote from: DW1961 on July 23, 2020, 06:10:26 pm ---
--- Quote from: capt bullshot on July 23, 2020, 05:08:48 pm ---Might be just for regulation and applied standards reasons.

Lighting is a different kind of equipment than e.g. a general purpose power brick, so it's tested and declared conforming to different standards.
I bet the load device (whether it's actual LED lighting or something else that can cope with the provided output) can't read that fine print and will just work ;)

--- End quote ---

Yeah, I think you are just right on that too. Reading this page really clarified things. Most all LED light strips or multi-light LED system us CV drivers. One poster above said it might be because ripple and some other undesirable artifact is present becasue it is a 'dirty' supply, but LEDs don't care about ripple (maybe). Constant Voltage is the LED standard.
https://www.ledsupply.com/blog/constant-current-led-drivers-vs-constant-voltage-led-drivers/

Incidentally, my SONY laptop power supply (made by Light-on) says CC/CV on it so I guess it can do both. That makes me wonder if laptops need both? IF so, we know for sure one reason that power supply says for "LEDs only."

--- End quote ---

CV/CC power supplies can be thought of as either maximum condition being met. So for a maximum of 24V and 2.5A, it will attempt to push 2.5A through the load, up to a maximum output voltage of 24V, or it puts out 24V up to a maximum load of 2.5A, after which the output voltage reduces to keep the current at 2.5A.

This would describe supplies designed for lighting, however I don't see why a laptop charger would function that way. CV power supplies generally have a hiccup mode when the max output current is exceeded. They don't gradually reduce voltage, it cuts out completely for a second or two then reattempts power.

I also wouldn't overlook the noise and ripple. LED installations involve long lengths of wire, which in conjunction with the power supplies inherent conducted interference can contribute to a noisy environment. In the past that has given me problems with magnetic pickups and noise on my scopes

You can always get a quality CV driver then use a second step down CC module to run LEDs. That's a more flexible way to implement dimming. I usually buy Meanwell drivers from the usual electronic parts suppliers. There's nothing particularly special about Meanwell, but they have a large range of voltages, power levels, form factors, CC/CV supplies etc generally at a decent price.

Also, avoid PWM dimming methods for controlling lights. They produce the most interference.

DW1961:

--- Quote from: capt bullshot on July 23, 2020, 06:31:21 pm ---
--- Quote from: DW1961 on July 23, 2020, 06:10:26 pm ---
Incidentally, my SONY laptop power supply (made by Light-on) says CC/CV on it so I guess it can do both. That makes me wonder if laptops need both? IF so, we know for sure one reason that power supply says for "LEDs only."

--- End quote ---

That'd be rather uncommon. Usual laptop bricks have CV output, and some kind of overload limiting / shutdown mechanism (which of course might be some kind of CC operation). I've never seen a laptop that relied on CC operation of its supply.

--- End quote ---

Well, that's Sony for you. This laptop is one of the last Sony manufactured, and it's 6 years old and I've had zero problems with it, including the battery pack.

DW1961:

--- Quote from: TimFox on July 23, 2020, 07:52:32 pm ---Reading the label, it appears to be a constant-current power supply for 2.5 A (2500 mA), with a compliance (maximum voltage across load) of 24 V.  However, I don't think that is correct:  instead it is probably a constant-voltage supply ("CV") at 24 VDC, with a maximum current of 2.5 A.  A switch-mode constant-current supply is great for driving LEDs in series without extra loss from a series resistor, but it looks like that strip includes SMD resistors.

--- End quote ---

It says right on it, "(CV)."

DW1961:
So the question remains, how do you know what DC supply to plug into a device? Will the device have that information on it? Or do most application use CV?

As long as LED strips have resistors, CV is the supply to use. According to that source I posted, CV power is virtually all applications for premade LED strips.

But what about other applications?

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod