I am very new to circuitry so this is probably a dumb question. I looked around for an answer but didn't find anything that I fully understood.

I have an LED light strip and a 12v portable power supply. The led strip is rated for 12v. I used a multi-meter to measure the power supply, it is outputting 12.4v. The LED strip has a safety switch of some sort that shuts the strip off when it receives too much current so that the strip doesn't get burned out. When the strip is connected to the power source it turns on for a second or 2 then shuts off. Some times it stays on a few more or a few less seconds.

I assume the strip turns off because the power supply outputs 12.4v which is .4v more than the LEDs are rated for so I want to reduce the voltage by 0.5v to keep the strip from turning off. What would be the best way to do this? I was thinking a resistor between the strip and the power source would do it but im not sure what resistor to use.

 

How much current does the LED strip require? The easiest way is to use a diode in series with the power source. A rectifier will give you a drop of around 0.7V, a schottky will give you around 0.4V. Figure out which one works better with the LED.

 

Ditto. Just be sure the diode you choose is rated for the current drawn by the LEDs. And for safety I'd want an amperage rating of 2x the LED current. This will ensure that it stays cooler and isn't too near the edge of burning out.

However, I'm a little surprised that 12.4V would cause your problem. Did you take this measurement under load, while the LEDs were powered by your supply? What sort of a supply is it? I'm wondering if it has ripple peaks to a voltage high enough to cause the LEDs to shut down. The diode may help fix this either way, I suppose.

 

Ditto. Just be sure the diode you choose is rated for the current drawn by the LEDs. And for safety I'd want an amperage rating of 2x the LED current. This will ensure that it stays cooler and isn't too near the edge of burning out.

However, I'm a little surprised that 12.4V would cause your problem. Did you take this measurement under load, while the LEDs were powered by your supply? What sort of a supply is it? I'm wondering if it has ripple peaks to a voltage high enough to cause the LEDs to shut down. The diode may help fix this either way, I suppose.

I did not take the measurement when it was under load. I just read it off of the leads from the power supply.
The power supply is portable rechargeable supply for powering gadgets such as phones and such, it has usb outputs as well as an output jack. The power to the output jack can be set to 12v or 9v with a switch.

 

How much current does the LED strip require? The easiest way is to use a diode in series with the power source. A rectifier will give you a drop of around 0.7V, a schottky will give you around 0.4V. Figure out which one works better with the LED.

I did some research into diodes. As I understand they allow flow in one direction but restrict it in the other. Do I position the diode so that it restricts the flow of electricity or so that it allows it? Does the diode still drop the voltage when It is oriented to allow the flow of electricity?

 

Do I position the diode so that it restricts the flow of electricity or so that it allows it?

You want the diode forward biased (so it allows current flow).

Does the diode still drop the voltage when It is oriented to allow the flow of electricity?

There's a voltage drop both ways.

 

I did some research into diodes. As I understand they allow flow in one direction but restrict it in the other. Do I position the diode so that it restricts the flow of electricity or so that it allows it? Does the diode still drop the voltage when It is oriented to allow the flow of electricity?

You want to allow the current flow (since "restrict" in this sense means to "block completely" except for a small leakage current).

The voltage drop when forward biased is nearly constant over several orders of magnitude of current. For silicon diodes it will be in the vicinity of 0.6 V (roughly 0.5 V to 0.7 V depending on the specific device and current),and for germanium diodes about 0.2 to 0.3 V. Schottky diodes have a wider range of forward voltages, depending on the specific device, and ranges from about 0.15 V to about 0.5 V.

How much current does your LED strip normally draw?