How to make Positive and Negative voltage

One of the most common question when it's about amplifiers is how to make +/- voltage needed for IC-s  for instance (TDA7294 or even amplifiers with complementary transistor). btw it's not like when you connect battery in opposite direction to voltmeter and it shows negative voltage!! There are two ways how to make Negative voltage. 

 * First and the easiest way is to use two the same DC power supplies. 

 How to connect it?

1. Connect positive(+/RED) terminal from 1st power supply to negative (-/BLACK) terminal on the second one. That will be your common terminal, ground, point whatever.
2. You are done, but you don't know it yet. Now you have common point and if you connect your  voltmeter(-) to common point and with (+) side of voltmeter to BLACK terminal it will show negative voltage while on the RED terminal will be positive voltage. That's it, instead of voltmeter you connect you own load or voltage stabilizer.

 *Here is the second way to make negative voltage, it's a bit complicated but not too much. If you understand basics of transformers and rectification then it's no big deal. ;)

 Parts you need:

• 1 - Transformer with 2 secondary
• 1 - Bridge rectifier or 4 diodes
• 2 - Capacitor usually 2200uF

Normal transformer with one secondary has 2 wire on primary(which goes to wall AC) and 2 wire on secondary(AC) while transformer with 2 secondary has 2 wire on primary and 4 wire on secondary. That's basic difference.

Now you have 4 wire on secondary. You have to connect 2 wire together but not from the same secondary it has to be one wire from first connected to one wire from second secondary and that will be your COMMON POINT. If you connect 2 wire from the same secondary you will make short circuit which can destroy transformer. So be aware what you doing.

With that COMMON POINT you have 2 more wires. These 2 wires have AC voltage you assume that we need DC voltage so we have to rectify it. You take these 2 separated wires and connect to bridge rectifier to get DC voltage. With 2 capacitors fix dumps in voltage and you are done. It will be more clear when you take a look at picture below.

I hope that negative voltage become more clearly now :) enjoy!
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