# Power supply for DDS Function Signal Generator

## How to build a power supply for DDS Function Signal Generator module

After building a DDS function signal generator I found out that, in order to power it on, it requires three different input DC voltages: 12V, -12V and 5V.

Obviously one can find a 12VDC power supply but I really don't want to use different PSU for each of those three voltages. So how to solve this problem?

Well, starting with 12VDC we can step-down and regulate the voltage to 5VDC quite easily. The easiest method is by using a LM7805 voltage regulator. OtherÂ  parts required are 2 polarized electrolytic capacitors (to filter the output) as shown in the schematic below:

OK, but how about the -12VDC? Well, this is a little bit more complicated in the sense that we are going to need more components which will result in a more complex circuit than the above. The circuit is based on a 555-timer IC and works as in the simulation below:

The schematics for this circuit (excluding the dummy resistor-LED load as in the animation above) looks like this:

So in order to make this circuit we are going to need the following parts:

• C1=10nF (tantalum)
• C4=22uF (polarized ceramic)
• C5=22nF (tantalum)
• C6=100uF (polarized ceramic)
• D1=1N400x*
• D2=1N400x*
• IC2=NE555N
• R1=4.8k
• R2=47k

(*) x=is anything from 1-7

So finally the aggregatedÂ circuit schematics of the power supply for DDS Function Signal Generator (including a 4-pin header) would look like this:

The input 12VDC can be obtained from a 110-220VAC to 12VDC (@1A) power supply that can be bought for less than \$2 from eBay.

The -12VDC output is obtained from the pin-2 of the header block.

The 5VDC output is obtained from the pin-3 of the header block.

The PCB board net routes can be arranged like this:

If you are using a perforated board instead of etching the PCB by yourself then perhaps the below board layout might help you. Please note that here I used jumper wires (red/blue) instead of copper traces marked with red/blue lines in the example above. The jumper wires are soldered on the back.

OK, soldering the parts was easy. Soldering the net could be a challenge depending on your soldering skills. The final circuit board could look like this (or better):

Note: due the fact that I don't have a 330nF capacitor I've replaced the capacitor C1 (330nF) in the above circuit with 3 parallel-connected 100nF capacitors. Their total equivalent capacity is the all parallel-connected capacitors, ie. 300nF.

Now, if you think that this article was interesting don't forget to rate it. It shows me that you care and thus I will continue write about these things.

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#### Eugen Mihailescu

Founder/programmer/one-man-show at Cubique Software
Always looking to learn more about *nix world, about the fundamental concepts of math, physics, electronics. I am also passionate about programming, database and systems administration. 16+ yrs experience in software development, designing enterprise systems, IT support and troubleshooting.

### One thought on “Power supply for DDS Function Signal Generator”

1. Boomer48

Some of these DDS board only require +9 to +12 volts because they generate the other voltages onboard. You have found an interesting use for the 555 but fewer parts are required if you use an ICL7660S. it is specifically made for that application and is exactly what the other DDS boards use.