Electronics > Beginners
Help me design a PSU
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nemail2:
i'm not entirely sure what you guys are talking about. i'm going down to 15 mV output voltage without any negative rail, as mentioned earlier.
BravoV:
Alternative design , -> General Purpose Power Supply Design

Quoting the designer ...

"... I am only looking a very low cost high performance regulator that could be controlled by just plain potentiometers."


Read the 1st post carefully.


A sneak peek on the spec (highlighted few items that might interest you) :

3V to 30V input source voltage range
1.5V dropout voltage
True regulation down to zero volts
1A output current with 0 to 1A current limit
High level of protection from loads.
Transient performance similar to the LT3080
No-load to full load output voltage regulation  better then 0.001% (Wiring and track resistance is the biggest problem)
Loads like a battery can be connected to the supply while the supply is off without causing any problems to the supply or the battery.
Design based on "garden' components - potential to make it very cheap.
Possibility of a wide range 1A supply using only board mounted devices and no heatsink.

Oh yes, no negative rail needed.  :P

A sneak peek ...



Again, you need to read the whole thread, just a suggestion.
Efe_114:

--- Quote from: rstofer on December 21, 2018, 01:19:29 am ---No matter what marketing says, rail-to-rail op amps can't go to 0V and still source or sink current.  They just can't.  Think about the active device that would be pulling down toward the 0V rail.  It has to have SOME voltage drop.

So, instead of having 0V as the lower op amp supply, we use -1V or so.

The problem is the spec and that is the death of most of these projects.  A) It's very hard to get to 0V.  Change the spec to "approach 0V" and accept 1V or 1.5V minimum.  B) Relatively high voltage and current spec (particularly current) when there is no possible use for such high values.  Somebody sees it written somewhere and suddenly 30V 5A becomes a thing.  Sure, the commercial guys can do it but they can get transformers wound any way they want and they can design in switching relays.  You just shouldn't drop 60V at 3A across the  pass transistor but the math is what it is!  Whatever the input capacitor voltage is, minus whatever the output voltage is, times the current, is turned to heat in the pass transistor.  Note that the heat goes up as the output voltage goes down!

In the days of CMOS, 100 mA is pretty high current.  1A is completely over the top.  Now, it's true, I'm not building audio amplifiers for a parade ground but those would have dedicated supplies anyway.  Around the digital bench, 1A is a LOT.  We also don't need variable voltage, 3.3V, 5V, +-15V covers just about everything.

Yes, when you are learning about analog circuits, an adjustable supply is nice.  But it doesn't need to go above 15V or above 1A.  I might build such a thing with an LM317 and call it a day.  BTW, I would pay a lot of attention to Figure 3 of this datasheet.

https://www.st.com/resource/en/datasheet/lm217.pdf

Don't overlook 5V 2A wall warts.  I use them all the time!

--- End quote ---
Dont get me wrong but i think you misunderstood something i am already planning for 15v 1A. i know 1A is a lot but i will use a power transistor so why not go up to 1A( i wasnt planning more than that anytime) i bought a 48 v transformer but that was for the kit someone posted a picture of.I will buy a lower voltage transformer specifically for this project which i think will be 24 volts or maybe 18 volts but 18 volt ones are pretty rare i will buy a toroidal one if possible. thank you for the suggestion so i will use ICL7660 charge pump IC to generate negative rail (-5 Volts) Also is it needed to make it with 15v/10v taps? I am deciding to use a 2n3055 so i think 15W max wouldnt be a problem for TO3 package. As i said i dont have much experience at all so i am planning all of these in theory So anyone here have more reccomendations to me about problems that will appear on practice?
Efe_114:

--- Quote from: spec on December 21, 2018, 03:06:05 am ---The ultimate barrier to getting true zero volts from a PSU without a negative rail, is leakage current. The output transistors leak current quite a bit and the killer is that the leakage current increases exponentially with junction temperature- take a look at the data sheet for your output devices.

Quite often with many PSUs, you are dissipating a lot of power in the output transistors, so the junction temperature is high and leakage current becomes a real problem.

But, bearing in mind that a PSU is a power amplifier, there is another aspect. If you have no way of loosing the leakage current, or you have no current drain on the output stage, you get into a no-mans land where the changing characteristics of the output transistors can cause problems.

The solution is quite simple though:
[1] Either generate a negative supply (2 x caps, 2 x diodes)
[2] Or use a power diode and a constant current sink, of around 20mA (power diode, 1 x small signal transistors, 1 x medium power transistor, 2 x resistors)

In general, a minimum constant current drain is good news as it also provides some current sinking in addition to current sourcing, which is handy for some loads.

Of course, the ultimate is a current sink capability equal to or more than the maximum source output current capability of the PSU (similar output stage to an audio or servo power amplifier). The LT1118 three terminal regulator, does this.

https://www.analog.com/media/en/technical-documentation/data-sheets/1118fd.pdf

--- End quote ---
yes im planning a 20 mA CC sink circuitry to serve as a minimum load.
Efe_114:

--- Quote from: BravoV on December 21, 2018, 09:13:26 am ---Alternative design , -> General Purpose Power Supply Design

Quoting the designer ...

"... I am only looking a very low cost high performance regulator that could be controlled by just plain potentiometers."


Read the 1st post carefully.


A sneak peek on the spec (highlighted few items that might interest you) :

3V to 30V input source voltage range
1.5V dropout voltage
True regulation down to zero volts
1A output current with 0 to 1A current limit
High level of protection from loads.
Transient performance similar to the LT3080
No-load to full load output voltage regulation  better then 0.001% (Wiring and track resistance is the biggest problem)
Loads like a battery can be connected to the supply while the supply is off without causing any problems to the supply or the battery.
Design based on "garden' components - potential to make it very cheap.
Possibility of a wide range 1A supply using only board mounted devices and no heatsink.

Oh yes, no negative rail needed.  :P

A sneak peek ...



Again, you need to read the whole thread, just a suggestion.

--- End quote ---
wow thanks thats really intresting i will read it. that specs are very nice. especcially the RED ones!
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