Below is my version of a power supply, current mode indicator (a touch of input offset voltage and hysteresis will be required for a practical implementation).
The C1815 should be OK but not advisable: the CEo is only 50V compared to 65V for the BC546.
The function of the BC546 is only voltage level shifting- no current gain is involved. The same current that is sunk from the emitter, essentially flows into the collector.
ok spec, now I did this: I made a hybrid from your drawing 2016_12_08_LM723_POWER_SUPPLY_V4_MOD1.png and my idea of using a series voltage regulator with a Darlington TIP120. I also introduced your substitute values for the voltage and current feedback circuit (18k to 47k and 82k to 230k, twice).
The value for R1 seems unchanged but I still have to update this after your post this morning about SOA.
Would you mind having a critical look at it please?
Thks, Erik
PS: somehow this drawing now appears on top of this post??? ..big enough?
Edit 13/12: corrected errors; replace 470R between Vc pin 11 and emitter 2SC1815 with a short, and add R11 (re. post 135)**broken link removed**
Edit 6/01/2017: replaced the series voltage regulator with a more stable version based on http://www.skillbank.co.uk/psu/vr2.htm, in the process introduced Q1 in the regulator.
spec, I think I was confused, I'll be back to the drawing board and review our last weeks' posts;
Erik
Edit: I forgot to mention, I also have to power a MCU and LCD display from the regulator, those are not shown here because they are beyond the scope of this thread.
spec, I think I was confused, I'll be back to the drawing board and review our last weeks' posts;
Erik
Edit: I forgot to mention, I also have to power a MCU and LCD display from the regulator, those are not shown here because they are beyond the scope of this thread.
Below is my version of a power supply, current mode indicator (a touch of input offset voltage and hysteresis will be required for a practical implementation).
Yes, an LM393 dual comparator. Sorry about the confusing sketch. I was not feeling too good yesterday- too much amber nectar the night before.
The principle of the constant current mode indicator relies on the fact that if ever the IN+ (+comp) input of the LM723 is more negative than the IN- (-comp) input, the power supply must be in constant current mode.
Yes, an LM393 dual comparator. Sorry about the confusing sketch. I was not feeling too good yesterday- too much amber nectar the night before.
The principle of the constant current mode indicator relies on the fact that if ever the IN+ (+comp) input of the LM723 is more negative than the IN- (-comp) input, the power supply must be in constant current mode.
Great! I will implement this one. Simple, effective and more economical than a software solution (time needed for programming, testing, calibrating, wiring.. ).
You need some more of this amber stuff, really enhances your thinking
Thks,
Erik
Great! I will implement this one. Simple, effective and more economical than a software solution (time needed for programming, testing, calibrating, wiring.. ).
You need some more of this amber stuff, really enhances your thinking
Thks,
Erik
Hysteresis on LM393: R1 from output to +IN, R2 from +IN to GND?
Say Vth (threshold, output voltage)=Vcc (18Vdc)*R2/(R1+R2), so if R1=18k and R2=82k (so that I can recuperate my previously discarded resistors from your calculations of my voltage- and current feedback circuits) then Vth=3.25V. Correct?
Hysteresis on LM393: R1 from output to +IN, R2 from +IN to GND?
Say Vth (threshold, output voltage)=Vcc (18Vdc)*R2/(R1+R2), so if R1=18k and R2=82k (so that I can recuperate my previously discarded resistors from your calculations of my voltage- and current feedback circuits) then Vth=3.25V. Correct?
I will give the hysteresis some thought- there are quite a few factors to take into account. The main factor is that the current limit indicator function must not degrade the fundamental voltage stabilization function.
The most important thing is that we have what appears to be a workable architecture for the current limt indicator.
Hi earckens,
In terms of circuit function, your new circuit and your previous circuit are the same.
The LM723 only needs around 14mA so the Darlington transistor is just adding to complexity and reducing performance- sorry.
Your previous schematic was OK.
Which previous schematic do you refer to spec?
I could use your straight zener regulator but I need a bit more current for a MCU and LCD; I toyed with your idea of keeping it simple but I decided to go for the darlington regulator because it still is a straightforward circuit and I would need it anyway.
I did some homework and verified the previous weeks' posts: my drawing of post 163 differs from yours', spec, in that I did not follow your use of a series zener for the voltage regulation (I use a darlington), and the voltage and current feedback resistor values have been corrected per your posts 113 ansd 119. Instead of a BC146 (Q6) I use 2SC1815 which is on hand here (Vce=50V, a bit too low, will be changed later to a better transistor).
Started up at 46Vdc and boem, the voltage regulator bust in smoke. Then tried the transfo separately but the primary fuse (1A-f) kept blowing, put in a 5A-f but then all house lighting down . I suspected an earth fault, removed the transfo and tried again with just AC and no rectifier and all ok. Checked the rectifier (50A beast) and AC to "minus" diode bust.
Did find a wiring error though ; too embarassed to say where.
Waiting for a new rectifier to arrive, but Friday we leave on holiday so the works will be for after the 28th.
Erik
I could use your straight Zener regulator but I need a bit more current for a MCU and LCD; I toyed with your idea of keeping it simple but I decided to go for the Darlington regulator because it still is a straightforward circuit and I would need it anyway.
The two VBEs of a Darlington will seriously degrade the regulation of the 18V Zener diode.
Not only that, but the extra current will be flowing through the current sense resistor and will mess up the current sense accuracy. Also, the processor and LCD, being digital, will introduce a whole load of hash into the precision voltage control and current control sensing.
There are three axiom in engineering:
make it modular
keep it simple
never compromise the core function
So it would be much wiser to keep the core voltage regulation functions isolated and separate from the processor and LCD.
Started up at 46Vdc and boom, the voltage regulator bust in smoke. Then tried the transfo separately but the primary fuse (1A-f) kept blowing, put in a 5A-f but then all house lighting down . I suspected an earth fault, removed the transfo and tried again with just AC and no rectifier and all ok. Checked the rectifier (50A beast) and AC to "minus" diode bust. Did find a wiring error though ; too embarrassed to say where.
Not only that, but the extra current will be flowing through the current sense resistor and will mess up the current sense accuracy. Also, the processor and LCD, being digital, will introduce a whole load of hash into the precision voltage control and current control sensing.
So it would be much wiser to keep the core voltage regulation functions isolated and separate from the processor and LCD.
I never did have a copy of that schematic; it is a schematic that you drew in EAGLE and attached to your post 123. It is still there- just click on the shortcut.
Hi earckens,
I never did have a copy of that schematic; it is a schematic that you drew in EAGLE and attached to your post 123. It is still there- just click on the shortcut.
The Zener is a nice stable voltage- that is what it is designed for but if you connect a Darlington's base to the Zener and take the output from the Darlington emitter, the two emitter/base junctions of the two transistors in the Darlington will introduce a varying voltage which will degrade the voltage stability. I hope I have read tour circuit correctly!
By the way, it is advisable to be cautious when using integrated Darlingtons because of their very low frequency response and and a tendency to generate distortion.
I see, spec; but (apart from the fact that I use a straight zener series regulator) there I still have a 470R R12 between pin 11 (Vc) and emitter of BC546: should that not be eliminated?
And change R15 (base of pnp TIP42C to emitter BC546) from 2k2 to 1k?
I see, spec; but (apart from the fact that I use a straight zener series regulator) there I still have a 470R R12 between pin 11 (Vc) and emitter of BC546: should that not be eliminated?
And change R15 (base of pnp TIP42C to emitter BC546) from 2k2 to 1k?