Wednesday, November 7, 2018

Fixing Lights with LM7800 Voltage Regulators

These LM7800 series chips are simple.

You choose the kind you want.  3, 5, 6, 9, 12 Volt Output and more.

The name corresponds to the voltage.  If you want 5 Volts DC like a USB port you need LM7805.
12 Volts like your car radio?  LM7812.

There are three pins.

Ground is the middle.  Negative wire.
The outside pins on both side?  Those are interchangeable - you choose.
  • One pin is your Positive Wire to the appliance/radio/light.
  • The other pin comes from the power supplying it. 

Either AC or DC.  It doesn't care.

Limitation is that if you want 5 Volts out, you need to feed it about 7 Volts in.  A little more in than out.  That loss is vented off as heat, so bolt it to the side of the container, preferably to metal.

Another way to describe it is that you can flip it over either way and start soldering.

Pin 1 Output Positive.
Pin 2 Ground - Negative for both Input and Output.
Pin 3 Input Positive or AC Signal.

The backstory is that there are a lot of Solar Powered LED Lights out there, as well as a lot of LED outdoor lighting.  They wear out.  Batteries last a year or two.  They get dropped and stop working like what happened with me this time.  They get hit by an errant pole or baseball.

You get the picture.

Most Low Voltage Outdoor Lighting works on 12 Volts AC. 
Most LED lights work with 3 to 6 Volts DC.

I tested my light that broke, the LED still worked.  It was as bright as the "working" lights when I plugged it into USB power at 5 Volts.

That meant I could fix it with a 25 cent chip and a little time.  Those lights are about 20 to 50 dollars.  They can be more expensive.

I chose chip and time.

It all fit inside the original housing once I cut the original power regulator and removed it from
the housing.  It wasn't even glued in place.

Soldered everything in place, and I now have a light for my porch.

Easy Peasy!

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