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Let's say I have a 12V LED, which can handle 2A, and a 12V 1A constant voltage driver.

Presumably, the driver will limit the current to 1A.

Is this a good method of limiting the current (assuming 1A is fine with your application) ?

What exactly about the driver limits the current, and could it be bad for the driver, that the LED would pull more if it could?

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  • \$\begingroup\$ How do you know the LED is rated for 12 volts? Where did you get the 'handle 2 amps' from? \$\endgroup\$
    – user105652
    Mar 3, 2018 at 21:58
  • \$\begingroup\$ The spec sheet of the LED \$\endgroup\$
    – djb
    Mar 4, 2018 at 8:23
  • \$\begingroup\$ Maybe the driver will limit the current to 1A, or maybe it will go bang. It's a maximum rating before you overload it. Unless it says it has a current limiter then it probably doesn't. \$\endgroup\$
    – user253751
    Mar 5, 2018 at 5:07

2 Answers 2

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Is this a good method of limiting the current

I would say No, it is not a good idea to rely on the maximum rated current of the power supply.

Usually the maximum rated current of the power supply is the maximum current it is designed to handle, this does not say anything about the actual current which will flow.

I can design a 12V, 10A power supply and sell it as "rated for 1 A" (because I'm an idiot or just because I feel like it). Then you connect your, say 10V, 1 A LED and you assume that my supply will limit the current to 1A. But that will not happen. My supply supplies 12 V and can deliver 10A if it has to (even though I rated it for only 1A). So your LED will get 12 V and perhaps draw 5 A, your LED will then be damaged.

In your case using a 1 A supply with a 2 A load is also a bad idea. It is very well possible that the LED will ask 2 A and the supply will deliver what it can deliver, which might be more than 1 A.

Problem is, the supply is rated for 1 A and when you draw more than 1 A, anything can happen. It could safely supply the higher current. More likely the supply will be overloaded and therefore overheat and in the end it will suffer damage.

You cannot and should not rely on a 1 A supply actually monitoring the current and regulating such that only 1 A will flow. Only Lab supplies with current regulation can be expected to do this.

The general rule in the case of constant voltage is that the current rating of the supply should be the same or higher that the current required by the load (your LED).

If you had a 12 V 1 A constant current LED driver then indeed you can use that with a 12 V 2 A LED. The LED would simply get 1 A from the driver and not burn at full brightness. But you mentioned that the supply is constant voltage so this does not apply in your case.

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  • \$\begingroup\$ Thanks, good info. Pity... I was thinking about maybe using a current limiting resistor, but the calculations all suggest that a typical resistor would melt pretty quickly in this situation. (P=IV=12W, R=V/i=12ohm?) \$\endgroup\$
    – djb
    Mar 3, 2018 at 22:29
  • \$\begingroup\$ @djb I am lost in how you get to 12V, 1 A so 12 W as that seems to ignore the LED. You will have to provide links to the actual products (LED, power supply) that you're using before anyone can make a proper suggestion about the possibility of using a current limiting resistor. \$\endgroup\$ Mar 4, 2018 at 11:36
  • \$\begingroup\$ +1 I'd also mention if I am tasked with designing a 12V 1A power supply, I'm actually going to design something that delivers more than 1A, probably closer to 2A. First it needs to run at 1A with tolerances of the 1A load, (way too many field returns if it cuts off at exactly 1A) and 2nd, It should not be overly hot at the max rated current. \$\endgroup\$
    – Trevor_G
    Mar 4, 2018 at 15:08
  • \$\begingroup\$ I think I have the info I need. I understand your questions. The details of the actual situation suggest that the LEDs will use 2.3V at .7A, and 2.5V at 1A, This means 25W total. I was wishing that a 12V 1A driver would limit the current to 12W. But it's not the case. It runs at 25W and gets hot. Surprisingly keeps going. Swapped with 12V 2A, and then driver is happy, but LEDs are running at double current somehow. Kudos to Cree. I want to maximize efficiency, and it seems like my only real option is constant current drivers. \$\endgroup\$
    – djb
    Mar 5, 2018 at 14:01
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Is this a good method of limiting the current (assuming 1A is fine with your application) ?

Your best bet would be to use an AC powered constant Current Mean Well HLG-40H-12B

Type B has dimmer wires that will dim by applying 0-10VDC or connect a resistor across the wires to set the current.

Mean Well HLG-40

Another alternative would be to use an inexpensive DC powered Mean Well LDD-L Series driver

Mean Well LDD-L

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