help-first project 20v dc power supply for amplifier

Thread Starter

tetropteryx

Joined Oct 18, 2023
8
I am pretty new to this stuff so im expecting that ive made allot of mistakes.
This is a circuit I piedec together from video guides and internet searches.
source voltage is in bottom left, 20 volt dc, there is a conversion to 9v dc for the 55 timer and the preamp and overdrive circuits (not pictured here) then im using mosfets to create 20v ac with a square wave. then im rectifying for +20v, 0v, -20v
any advice opinions and warnings about how it will all catch fire would be appreciated, also im really unsure on some of the resistor, diode, and capacitor sizes in the square wave inverter/rectifier.
 

Attachments

dl324

Joined Mar 30, 2015
16,679
Welcome to AAC!
using mosfets to create 20v ac with a square wave. then im rectifying for +20v, 0v, -20v
If you're starting with a 20V supply, why aren't you just using it for the amplifier? To get -20V, I'd use an inverting switching regulator.

What is your amplifier's sensitivity to supply noise?

This is the basic topology for making an inverting switching regulator:
1697680264484.png
You change the ratio of R1 and R2 to get a different voltage. You haven't mentioned current requirement, so can't give more detailed information.
 

Thread Starter

tetropteryx

Joined Oct 18, 2023
8
Welcome to AAC!

If you're starting with a 20V supply, why aren't you just using it for the amplifier? To get -20V, I'd use an inverting switching regulator.

What is your amplifier's sensitivity to supply noise?

This is the basic topology for making an inverting switching regulator:
View attachment 305294
You change the ratio of R1 and R2 to get a different voltage. You haven't mentioned current requirement, so can't give more detailed information.
I didn't know they existed. My Google Foo failed me.
This looks great. Current requirement are 1.5 amps rms 3 amps peak I think.
 

dl324

Joined Mar 30, 2015
16,679
My Google Foo failed me.
It helps if you know what to search for.

MC34063A is a very old design and supply ripple isn't insignificant. I tend to use it because it was among the first designs I used to make switching regulators when I was a newbie.
This looks great. Current requirement are 1.5 amps rms 3 amps peak I think.
60W power supplies aren't exactly a beginner project.
 
Last edited:

Thread Starter

tetropteryx

Joined Oct 18, 2023
8
"60W power supplies aren't exactly a beginner project."
I wasn't aiming this high exactly, but allot of amp kits and diy amp circuit are running tubs and hundreds of volts.
I've built things before, a 3d printer and such. Just putting the pieces together and following guides.
I found some guidance on an audio amplifier ic for the power amplification and I've been sizing things to match to an extent.
20 volt seemed like a good place to be voltage wise because it was in the range of that amplifier and pretty easy to set up a battery and charging for. I'm hoping to use a usbc pd charger and cord.
 

dl324

Joined Mar 30, 2015
16,679
The original circuit I posted. I may never build it but I was learning allot from it. I'm hoping I didn't learn all the wrong things.
It won't work.
  1. The signal out of the timer plus MOSFETs will always be positive, so you can't generate a negative voltage.
  2. You're starting with 20V, so you'll lose 1.4V in the +20V section.
  3. You're going to get very little current with those 1k resistors.
  4. I can't decipher the connections on the two bridge rectifiers. You have the connections on D7 going through capacitors.
  5. I didn't calculate the timer frequency (or check to see if it would actually work - supplying it through a wimpy voltage divider is questionable).
  6. The 2.2mF capacitors aren't needed.
  7. I assume 1mF means 1000uF.
  8. D3-5 serve no purpose.
  9. What is the purpose of the multiple grounds? You can only have one.
  10. Though you can't blindly trust simulator results, this one is telling you that the circuit doesn't work.
I don't know where you got the circuit ideas, but they're mostly garbage.

Regarding your drawing style:
  1. Do the green and purple colors mean something? If they don't, you shouldn't use them.
  2. That grid, and the lack of connection dots, is distracting.
  3. There are very few cases where wires should be drawn at angles of other than multiples of 90 degrees. Your schematic doesn't have any of the exceptional cases.
  4. You shouldn't have text on top of wires.
 

BobTPH

Joined Jun 5, 2013
8,663
Get two 20V supplies that are isolated. Connect the positive of one to the negative of the other. That connection is ground, and the other two are +20V and -20V.
 

Thread Starter

tetropteryx

Joined Oct 18, 2023
8
It won't work.
  1. The signal out of the timer plus MOSFETs will always be positive, so you can't generate a negative voltage.
  2. You're starting with 20V, so you'll lose 1.4V in the +20V section.
  3. You're going to get very little current with those 1k resistors.
  4. I can't decipher the connections on the two bridge rectifiers. You have the connections on D7 going through capacitors.
  5. I didn't calculate the timer frequency (or check to see if it would actually work - supplying it through a wimpy voltage divider is questionable).
  6. The 2.2mF capacitors aren't needed.
  7. I assume 1mF means 1000uF.
  8. D3-5 serve no purpose.
  9. What is the purpose of the multiple grounds? You can only have one.
  10. Though you can't blindly trust simulator results, this one is telling you that the circuit doesn't work.
I don't know where you got the circuit ideas, but they're mostly garbage.

Regarding your drawing style:
It's a simulator program called Proto. I don't love how it looks but I can try to remove issues such as angle paths and text over paths. I find the grid helpful.
Also the simulator shows the circuit working but I don't know how to test amp draw capacity.
One of my primary questions for yall is sizing components such as capacitors and resistors.
The frequency of the timer seems like it would be related to amp draw , like how many amps the capacitors can deliver during a pulse. But I don't know if any number is too fast or too slow. I had it set at 60 hz. I doubt that's optimal. It's just what I had going.
 

dl324

Joined Mar 30, 2015
16,679
I find the grid helpful.
It might be for schematic entry, but it's distracting when you're trying to read it. Especially when the grid in some places looks like it could be a connection dot (which you don't appear to be using).

If you have wire crossings without "humps", you must use connection dots. Some use "humps" and "dots" but, thankfully, that style died out in the 1960's.

The schematic editor I use (Eagle) typically requires me to enter connection dots explicitly.
Also the simulator shows the circuit working but I don't know how to test amp draw capacity.
Assuming that the MOSFETs are turning on and off (can't tell because you didn't give a part number). The positive supply should have been closer to 18V and the negative supply would have been more than -1mV. With no load, you'd be seeing the maximum possible voltages.
One of my primary questions for yall is sizing components such as capacitors and resistors.
There is no general rule for selecting component values. You're going to have to ask more specific questions.
 

MisterBill2

Joined Jan 23, 2018
17,800
NO, it will not work! If you sre driving bridges in parallel froma single source you can't put the outputs in series. That bridge "box" contains 4 diodes. Draw in the diodes and then examine the circuit and you will see the problems.
 

Audioguru again

Joined Oct 21, 2019
6,610
The IC with no part number is probably an NE555. Its supply voltage is probably bouncing up and down since it is missing an important supply bypass capacitor at its pin Vcc, use 220uF to ground).

The gates of all the Mosfets are floating since they are missing a resistor to ground to turn them off.

The very high 1k resistance of R5 and R7 limit the current feeding the bridge rectifiers to only 10mA.

I did not look to see if the bridge rectifiers make +8.6VDC and -8.6VDC.
 

MisterBill2

Joined Jan 23, 2018
17,800
Considering the fact that the supply starts with a reduced voltage, it would make sense to use a standard transformer power supply and not have to struggle with optimizing a switch mode supply. Even if you go to the TI website and use their switcher supply design program, a transformer supply will be simpler and quite probably more stable. And it will function properly the first time.
 
Top