how to use a ic 7818

Thread Starter


Joined Jan 29, 2012
ok, lets be frank. i have a old power supply that gives 240 - 12v AC, i rectified it using 4 diodes, i think they were IN 4007. now i get a voltage of 26v dc. viewing various threads on this forum, i realize that it is a normal thing to happen. i also understand that using a ic 7818 or a 7824 i can convert the same to 18v or 24v. my question is which pin should be the input, which should be grounded and which should be the output to the circuit. i tried pin 1 as input, pin two as ground, and pin 3 as output of pin connected to circuit. I still get 26V instead of 24 v. I reversed the in and out and i think i blew the 7824. the thing does not seem to work thereafter. I am new to circuits. I need to connect a 300 led panel using a series and parallel array. can somebody help me with how to connect the 7818 and 7824 ?????


Joined Dec 20, 2007
Why don't you look at the datasheet from a manufacturer of the voltage regulator IC? It shows which pin is which, the important input and output capacitors needed and all the details about cooling it and other things.

Your 12VAC transformer has a loaded peak voltage of 17V and the rectifier bridge has a loaded loss of 2V. The main filter capacitor produces a ripple voltage loss so the transformer is no good for an 18V or 24V voltage regulator IC.

Using voltage regulator ICs and connecting LEDs in series with a calculated current-limiting resistor use simple arithmatic.


Joined Nov 25, 2009
Most likely the 78XX won't supply the current you need. What is the array's layout and what type of LEDs are you using? 3mm, 5mm, 10mm?