Now it is time to provide an appropriate voltage supply for the audio-amplifier. Since I care about the noise and the amplifier is dedicated to work from the outlet only, I decided to move in the linear stabilization direction.
What do I want?
- The +12В voltage for coolers and relay, which in charge of the stand by mode.
- The +5В voltage for everything else, I have a lot of “everything else”, so I need to project a lot of different connectors.
- Powerful output capable to provide enough of the power for everything I have.
- To not forget to put all powerful transistor underneath of the radiators and coolers.
- Add outputs for indications and switches.
First two bullets I solved by linear stabilizer ICs – 7812 and 7805, they will provide proper voltage levels for us.
The third one is more complicated – those ICs are capable to provide up to 1A, and it might be not enough, especially during peaks, to solve the issue we could use a single resistor and the powerful pnp transistor, for instance TIP127.
When the current reaches 100mA value, the voltage drop on the R2 is equal to 0.5V, which is enough to open the Q1 transistor, which will route the biggest portion of whole current. The voltage at the output still will be the same. This application schematic could be found in the 7805 datasheet.
Thus, we boosted our maximum current up to 5A, should be enough.
Also, the pcb will have transistors, used for coolers control (driving + PWM). Everywhere I placed LED placeholders if I will want some indications apparently.
Summing up, the pcb schematic:
I went to the market to gather all the supplies, and found myself unpleasantly surprised by the 20 W transformer price, it was a big deal for me at the moment. I did not want to put a lot of money to the DIY amplifier.
Then I was digging in my stashes and finally found some commercial dc-dc supply source with 5V and 24V outputs, I had changed a schematic a bit:
In fact, it is almost the same schematic, like the first one. I just removed the passing transistors and input networks. Each control input has both header and the transitor bufer – so it can be controller either manually or by microcontroller levels.
Everything tested and works, so far so good, will see how it will evolve.