LCD monitor Switched Mode Power Supply

Posted on Feb 5, 2014

This is a simple and effective switched mode power supply (SMPS) that I built to power a LCD monitor that I fixed a while ago. This one requires 20V at 2. 3A, but the PSU output voltage can actually be set in the range 1. 2V - 25V, with a small variable resistor (R3 in the schematic below). It uses a LM2576-ADJ regulator which requires very few exte

LCD monitor Switched Mode Power Supply
Click here to download the full size of the above Circuit.

rnal parts and as you can see from the schematic of figure 1. I didn`t go much far from the bare application example, that you can find in the National Semiconductor datasheet. There you can also find the required calculations necessary to obtain all the part values that surround the regulator, in particular the coil inductance and output capacitor. The regulator can sustain 3A output current which is more than enough for the required 2. 3A of the LCD. It uses the simple buck-converter topology which allows to obtain a fairly stable and regulated output voltage. The switching mode approach dictates a much better efficiency than the linear regulator normally used in simple circuits. I designed a simple one layer PCB layout, with wide traces for the paths where the current is substantial, maybe too wide ;) (see figure 2. ) You can get both the schematic and PCB in the Eagle file format from here. In figure 3. and 4. you can see the power supply already assembled and with the load (monitor) applied. You can notice the big yellow switching toroidal inductor. I got its core from a broken PC power supply and patiently winded the dozens of turns with wire I had laying around. The remaining parts I salvaged from the junkbox, except the regulator which I bought from an online electronics distributor.

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