That page is fantastic indeed :-)

. ....

haha my exact thoughts

@@greatscottlab......Dave Plumber from Dave's garage could use your help......he is the retired Microsoft software engineer and tons more cooler stuff.....he's got a problem with negative voltages and addressable leds

Yeah, your intuition would tell you +12 + -12 = 0.

24v rms peak to peak, but still

That's why you shouldn't become part of the circuit.

Minor correction here... It's not when you "tie +12 and -12 rails together" that you get 24v, because if you did that then you would short out the power supply, possibly causing damage to it... Instead, it is rather when you measure across or put a load across the -12 and +12v output terminals of the power supply, that THAT'S when you get 24 volts.

@@JoeJ-8282 Cmon man, that's just being pedantic. Everyone knows what I meant.

though that seems only gd for pre amp...power amp....just to low power

Another way to create negative voltage is also to: - use one diode as a voltage dropper, okay for low power IC that require small biasing to allow output voltage go to GND - use isolated power supply and connect them in series, for example use isolated 5V-5V module and connect it +out pin to -in pin to create +5V and -5V

Old serial ports used that voltages, but in ATX power suppy its has easy obtained from a inverted diode on the 12V line right out the transformer...

@@servantsochrist the -12v rail is pretty low power (usually under 2A)

@@vincentschumann937 yes...only good for line level stuff...op amp logic.... but enough to run headphones i guess...nothing more....or just a ref voltage for whatever your use case

Well......

😂😂😂👌

Not allways. For example if you need a Positive *and* a negative voltage.

But if you want a rail to rail output from a simple dc you will need his video 🤩

@@flos251 I expected you to take it as a joke.

Glad I could help :-)

Why was it? lol.

Also some old HP modems uses -78 volts, always wondered...

Thanks for the feedback :-)

Why would you need to "When combining 2 outputs of a transformer on both ends to increase the amount of current, you must do that after the bridge rectifier you should use for each... Learned that the hard way ;)" If you don't swap the polarity of the windings it should just act as a primary with more thicker windings

@@alexstone691 Yeah but on some transformers the two center taps on the secondary side are connected to each other

@@alexstone691 Those windings are never exactly the same, so you get some strange currents flowing. When combining it from 2 separate transformers you must for sure match polarity and still may see the same 'strange currents'. When I started learning about electronics (begin '90s), it took me quite a few fuses to find out why they blew so quickly. Glad I used fuses in my designs back then ;)

actually, it will still work. It will even work off of one winding. The problem with this one-winding setup is that if the current consumptions on the two rails differ, that difference current will appear as dc across the winding, causing core saturation. That makes the transformer roar and heat up unreasonably.

You'll probably find that even repair places that actually repair the boards probably wont have what you need for you project since most modern electronics use SMD components, they may have some through hole lying around for fixing older electronics but I wouldnt count on them magically having everything you need and I very much doubt they would have components unrelated to TVs, computers or phones, so probably would not have variable resistors, usable displays (they would have ones for phones but they are pretty much unusable), motor drivers, leds, anything like that. If they wanted to sell components to hobbyists then they would open a shop not a repair business, it is probably a bit of hassle for them to sell to you even if they have what they need. The employee would probably have to ask their boss, and then find out how much it costs them and then have their boss decide how much they will charge you for it, essentially it could take a while and be very inconvienient to them because they arent set up as a shop to sell components to hobbyists. It isnt cost effective for a lot of these repair shops to actually fix the board, it is cheaper and faster to just replace the broken parts and it means they dont need to hire someone who can replace SMD and BGA components. Also repairing the boards would take time to track down the exact cause of the problem, its a lot easier to discover the problem is with this board, rather than this exact component on the board. They would have to first identify the exact component on the board that is damaged and then replace it, which not that many people could do anyway, especially if it is very small SMD components or BGA. Then it may not be the only damaged part. They also need to have access to datasheets and schematics to fix all but the most basic problems, which the manufacturer wont publically release. Then there is the problem of sourcing the components, since some might not be publically available, or the ICs dont have any markings or dont show up when you google them. It is by far easier just to order the boards to replace them with. It also means they dont need to hire an expert to fix the boards. An expert would still take quite a long time to fix a phone for example, and in that time, a lower paid employee could replace the board and have multiple phones fixed. These repair workers that just replace the board do still have to have knowledge and experience of what to replace and why and have knowledge of lots of different devices, so just because you are a hobbyist doesnt make you automatically better than them. In a lot of cases mechanics are the exact same, they just replace parts, whether or not that is because they cant fix them themselves or not is irrelevant but most kinds of repair work is just replacing parts as quickly and cheaply as possible.

Yep, that old adage 'Time is money'. No job satisfaction with just replacing boards.

nice tip... gonna use that thanks

What about using two identical single output transformers and connecting their primaries in parallel, then connect the secondaries in series (essentially making a center tap) and connecting that to ground?

@@MuhammedGemci, I think that ought to work, but be careful with the polarity.

Good to know :-)

many pc power supplies have a - 5v rail and a -12 rail generally the white and a blue wire

@@ShahZahid yup that’s why I save my old atx’s lol.

@@greatscottlab Was hast du dir bei deinem Kanalnamen gedacht?

Great :-)

Glad I could help!

Glad I could help :-)

True👍

Two supplies is an elegant and simple solution, although it's not based on a single circuit. I used this option when I was studying op amps and I had no time to build a dual-rail-supply, neither wanted to buy one.

Brilliant :-)

yeah, super short circuit current from doing that, things puff up the smoke real fast

I think the circuit started without a true ground signal to begin with, only the first 3 out transformer had true ground.

But what is "true ground"? Are you guys talking about the Earth pin in your wall mains?

​@@Nintendjyes

Glad it was helpful!

You can also use almost all Buck Converter Modules. Connect the + Supply with Vin of the Module, GND to Vout of the Module and You will get the negative Voltage at the GND-Pin of the Module. The Summ of Input Voltage and negative Output Voltage has to stay below the maximum allowed Input-Voltage of the Buck Converter Module.

@@juergenschimmer960 True, but I'm not sure if it can be accomplished with a synchronous rectifier where the "diode" is instead a MOSFET, and built into the chip. The other downsides are the large inrush current and the fact that the output tends to be noisier compared to when not generating a negative voltage. I've solved this in the past by adding another inductor in the series and an additional output capacitor, a pi filter.

Thanks for the feedback :-)

But then what happens when you load down one of the rails but the feedback resistors are on the other?

7805’s output stage is not bipolar, so I’m not sure if you can sink significant current into its output without it misbehaving. If you want to use linear regulation, you’d be better off with a power opamp as shown in the video since these devices are designed to work correctly for both sourcing and sinking current.

Oh no? What do you think is inside 7805’s?

Yeah flyback converters can be used, you only need to flip the secondary transformer to get a negative output There's a lot of flyback converters that include both a positive and negative branches, with 2 secondaries windings on the transformer and essentially the same circuit as the output

Thanks 👍

@@greatscottlab Welcome 😘

Glad it was helpful!

Me too brother.

Hope you enjoyed it!

Glad to hear it!

Thanks :-)

No problem!