Another Discrete Regulator

Hello, it is a good realization! To improve the output load capacity, it would be possible to use an n-MOSFET instead of a Darlington transistor.

@PrathikP, where is my comment, have you republished this circuit?

http://everycircuit.com/circuit/5844372858601472

set the mosfet Vto to realistic 2V or even higher and a BJT darlington will perform better

Yes @hurz I republished. Some user posted a 1000 circuits. And why do you want me to set the TL431 MOS to 2V?

@walkemm an all MOSFET version (or mos bjt hybrid) is coming up next. And I see the voltage reference work around. I think I shall use that next time.

i have said 2V no i didn't

my comment were related to this part of text in your description "I know that a TL431 isn't quite discrete" and i tried to interpret what you mean. Nothing else

set the mosfet Vto to realistic 2V or even.... This was your comment

Oh I see

must be a typo or you remember wrong. You havn't read my xomment

bring it back and lets see

I meant using a tl431 doesn't make this regulator a discrete one. I was unable to make a stable discrete voltage reference.

Bring it back? What does that mean?

Oh I think you're talking about the old post. I didn't see the comment in that. I deleted it

i still dont understand what you mean, and i commented it with. A complete discrete TL431 would be bigger then your circuit of regulator. TL431 needs maybe about 30 BJTs!? And i recommended also the oposite situation to use a DC voltage source as 2.5V reference. Cuz you were complaining about the Mosfet model. Or something i dont get

set Vto to 2V you have dreamed, sorry

Now i think i understand. It is your taget to get rid of ICs loke TL431 is as i said. Right. So even more correct to think about the possibility to exchange the TL with a voltage source. E.g. if your input voltage is stable you can derive a reference voltage from it. Sure it depends on how stable you want this regulator

bring it back, means take the old circuit from trash to your wirkspace and save it as public again and we can see what i have commented

if you deleted it, then its still in Trash

I don't want to make a discrete tl431. I just wanted to make some discrete voltage reference. I wasn't able to do it, so I used a tl431. That's why I said "this circuit isn't entirely made up of discretes any more".

The 2 volt comment is from this thread itself. You made that comment 1 hour ago. "set the mosfet Vto to realistic 2V or even higher and a BJT darlington will perform better" is what you said. I don't really know what that means. Oh and my trash is empty.

The comment that I quoted is after walkemms last comment and my first comment. You posted it 1 hour ago.

check the link from walkemm or so it was related to his link and circuit, not to yours

because he is runnig around and telling his mosfet version is better then yours with darligton. But he uses an totaly untealistic mosfet with 0.43 V Vto ! If he sets his Mosfet to Vto 2V then the advantage above a darlington is lost, cuz Vbe is below 2V.

and at the end its totaly unimportante across what component the power is wasted, if BJT or Mosfet that doesn't make any difference. What makes a difference is the low drop and with a Vto of 2 or maybe even 3, 4V his mosfet solution stinks.

Oh that was meant for him, ok. Actually I prefer using a mosfet. Ofcourse, the Dropout voltage is higher, but it is voltage controlled because of which the circuit current draw reduces significantly. And using a mosfet always works out better for me. I get better regulation with MOSFETs.

Ofcourse, it's good to have a low dropout, and that can easily be achieved using a PMOS, like In my previous circuits.

And you can't get low dropout with any transistor using this circuit. The output of the error amp doesn't go to zero. It can't pull the gate of a pfet to zero.

PMOS are bad in performance and expensive with comparable performance like NMos, desingers try to avoid PMos for that reason. The current for a darlington in low because of its high overall beta which is a product of both trasistors, your low power one and even the power transistor are on pessimistic default values 100. I expect much higher values in real for both. The base current should be minimal even for 10A load e.g. beta 500 and 150 for 10A load would result in 133uA which is nothing

Oh ok. But if you want low dropout I guess there's no other way, cause bootstrapping isn't possible here in this non-switching system. But like i said low dropout isn't possible with this exact control circuit so using an NMOS/NPN would be better then.

An NMos would drop at least Vto !!! Plus a few milli volt Vds. But the issue with a NMos is its high Vto 2V or more, and this is also what you will drop and more! This is the problem with common drain circuit ! Minimum Vto plus an overdrive voltage!! e.g. Vto=2V means Vgs + 5V = 7V but you habe still no overdrive, calculate Id and with 10V supply there are only 3V left for overdrive, question what is the maximum current with 3V Vov ? Back to drop, the minimum drop voltage is Vto for a common drain topology. Ar around 7V Vgate you can have at source 5V, and if you need some current at regulator output, Vgate must go up!

Hmm yes with the IRF540N it's 5V Dropout at 5A load current.... A Darlington/sziklai would be best. Usually I use a PMOS and that gives me a low Dropout, so I assumed blindly that the NMOS solution would have a decent 3V dropout.....

@Nian_Zhoe former @lenzrulz suspended liar/cyberbully since 28Feb2020

Umm you delete your comment @Nian_Zheo and your spamming again?

back to an discret reference voltage, the keyword for you is bandgap. All examples i had are gone with robbi_kiddi and @lenzrulz SPAM attacks. But maybe i do one more. but the tasklist get a little over filled

I'll take a look at it. And I found this simple trick http://everycircuit.com/circuit/6309903592062976

Ofcourse, these circuits have a high temp dependence and all that, but for now I'm just trying to keep the line and load regulation as low as possible. I'll worry about temp co later.

Line regulation is quite shitty in the real world (as expected) at 0.4%, but the load regulation seems to be good (lost the data for that, but I remember the op voltage was stable). This is for the first circuit with a tl431 reference.

Here we go i found some material you can think about. The principle is the following. You have two current sources one linear and another one is exponentiell rising. If you overlay both functions, they will cross at a point where the exponentiell function overtakes the linear one! This is the so called bamdgap point. This word "banggap" here is wrong cuz the functions are not made with bjts and only its thresholds, here we use resistors and lets say we reuse this principle in a macroscopic way. But its working find. Additional to this circuit there are nice tricks to thermal compensate such kind of circuits, but for you its in first step interessting to make a stable reference voltage! Be carful this kind of circuits have its math and problems, one is, there is one more point of crossing and give a solution for the difference OpAmp !! Work it out, telling you all secrets is boring. Tipp, think about startup! Hope thats fun for you! http://everycircuit.com/circuit/6172801899692032