Electronics > Beginners
Discrete Regulated power supply
not1xor1:
--- Quote from: blackdog on June 27, 2018, 05:55:22 pm ---Hi not1xor1,
Yes, its and, and bad :-DD
First short circuits and gone is the 2N3055 |O
The 220uF capacitor has a good funtion, and that is to keep the current trough R3 (Basis Q1) free of hum.
A extra resistor between C3 and Q2 would resolf a big part of the extra pole.
But... it is still bad! :box:
The Elektuur design from december 1982 is a bit slow but a good design to start.
It is not to difficult to make it better, but won't advise this for this beginners section.
Kind regards
Bram
--- End quote ---
I do not agree about the 220µF capacitor. It affects the transient response much more than the output capacitor.
The right way to reduce the ripple in that kind of circuit is to use two resistors instead of just one (i.e. R1).
For instance a 1.5k resistor plus the 220µF capacitor would reduce by a fair amount the ripple, while another 1.8k resistor would improve the transient response.
Besides that ugly circuit, the Elektor circuit diagram, is affected by the same problem. Even just 4.7µF is enough to produce a really ugly transient response.
That capacitor was probably added as an afterthought because that circuit oscillates badly without it.
It is just a matter of ignorance. The BJTs composing that sort of sziklay configuration are badly polarized and do not work at their best.
Just a couple of resistors between the base and emitter of T1 and T2 make the circuit behave properly and the 4.7µF (C2) capacitor is no longer necessary to avoid oscillations while the transient response is greatly improved.
There are other bad design choices and other possible improvements in that Elektor circuit, but I'll leave that to another future post, if anybody is interested.
Elektor schematic LTspice circuit simulation (current limit removed)
Output ripple at 2.5A load
The ugly transient response from 100mA up to 2.5A
The current through the 3 output BJTs
Better BJTs polarization and a little improvement in transient response
Modification of the compensation network and better transient response
HoracioDos:
It's very interesting to see how analysis and improvement is done.
Could you please tell transient and load parameters.
Thank you very much.
--- Quote from: not1xor1 on June 29, 2018, 03:15:04 pm ---There are other bad design choices and other possible improvements in that Elektor circuit, but I'll leave that to another future post, if anybody is interested.
--- End quote ---
I'm interested but I don't want to take advantage of your generosity
techguru:
thank you not1xor1 sir,
As a student give me the path by which you have acquired this knowledge. No text book worries about gain and phase margin.
not1xor1:
--- Quote from: HoracioDos on June 29, 2018, 05:08:34 pm ---It's very interesting to see how analysis and improvement is done.
Could you please tell transient and load parameters.
Thank you very much.
--- Quote from: not1xor1 on June 29, 2018, 03:15:04 pm ---There are other bad design choices and other possible improvements in that Elektor circuit, but I'll leave that to another future post, if anybody is interested.
--- End quote ---
I'm interested but I don't want to take advantage of your generosity
--- End quote ---
I do not have much time at the moment.
Anyway I found a good solution to make a simple yet better current limitation circuit. I also replaced the two zeners with a TL431.
According to LTspice the circuit even behaves nicely at turn-on and turn-off with the output voltage increasing/decreasing slowly.
In a couple of days I hope I'll be able to post a zip with the various models and test circuits.
blackdog:
Hi,
No Spice for me, just solder. :-DD
I hackt the schematic and below you can see the result for now.
Selecting and measuring the transitors with a cheap China meter, handy!.
Testing the current source and the zener with a variable power supply to see how mutch the zener voltage wil change.
I am now about half of building the circuit, the transistors 1 and 2 in the schematic are tight together for better thermal behavior.
I have adapted this version so that I can supply 22V and 2-Ampere.
If the circuit works, I will test the dynamic behaviour of this circuit.
The reason for using a modern power transistor is that it will then be easier to keep the circuit stable.
I have to confess that I have never built a Power Supply with a Darlington that has three transitors.
Probably there will be another HF stop resistor around this transitor.
Because I would like to have a reasonable noise / hum free design, the number of parts used is increasing rapidly.
And also three extra diodes for safety.
But be aware that with two opamps and a TL431 you can make a better power supply! :-DD
Why then all that effort to even build it, because I like to keep everything discreet and also just to play with it...
Depending on my work in the coming week, I will show the outcome of the above schematic.
Kind regards,
Bram
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