trying to regulate voltage for power supply

Thread Starter

Evan Moore

Joined Dec 18, 2021
8
I am making a variable power supply, and I have everything that I need in theory. I will take 120V AC from an outlet, then use two transformers, 115V to 60V and 115V to 60V centertapped, which will then be rectified and sent through a low pass filter to obtain three lines of +6V, +30V, and -30V, in reality the ouputs will be around +7.7V, +42.3 and -42.3. After that I plan to regulate the voltage with zener diodes, to obtain three stable lines to go to the part that modulates the voltage. I will use 3 555 timers that will probably get their power from the 6V line, using the timers I will be able to get 3 PWM signals, which will then be fed through a low pass filter in order to get a variable analog voltage (I originally planned to use a LTC6992 in order to get the PWM signal but it only comes in surface mount, and my hands are too shaky in order to get it on the breakout board). after I get the analog voltages, it will go into 3 op-amps each with an appropriate amount of gain, to get the desired voltage. After that it will go to the output of the power supply, after going through a voltmeter and ammeter. The issue I am currently facing is that in the simulation I am using, not only does the voltage after the regulator not stay at the desired zener voltage, whenever a load is applied, the output of the regulator drops proportionally to the load applied. Here is the circuit simulation, the left half is the rectification, and the second is the regulators. Note that whenever a resistor is put between an output line and the ground, the output voltage drops, is there any way to prevent it dropping? If that is not possible, is there a way to minimalize the output drop until the current draw reaches an amp?
 

Papabravo

Joined Feb 24, 2006
21,305
So you do realize that Zener diode regulators are just about the worst regulators you can build, with no feedback, and poor transient response. There are very good reasons a good bench power supply is not an inexpensive toy. Also, it is unlikely that you will be able to use opamps for the power output, that is not generally what they are able to do. That said, a better schematic, with part numbers and so forth may help us guide in a more productive direction.

You might want to start with some explicit requirements, such as
  1. +6 volts @ 3 Amperes, short circuit protected
  2. ±30 volts @ 1.2 Amperes each
To this you might wan to add a specification for the allowable ripple, such as
  1. 50 mV P-P on the +6 volt output
  2. 15 mV P-P on the ±30 volt output
Keep in mind that tight specifications will raise the final cost and complexity of a design. Each requirement in and of itself implies compromises in the design
 
Last edited:

LowQCab

Joined Nov 6, 2012
4,290
Are You trying to get your rather strange Simulation to work,
or are You trying to design an actual Power-Supply ?

Did You use 2-Transformers because You already have them,
and want to use them for this project ?

If You already have the Transformers, what are their VA-ratings ?

Are You expecting to build this with "Junk-Drawer" or "Jelly-Bean" parts that You already have ?

A "Variable-Power-Supply", that's a very broad statement ............

What is the specific Voltage-Range that You would like to have ?

How much Current do You expect from this Power-Supply ?

Do You want adjustable Current-Limiting ?

What is Your acceptable level of Ripple on the Outputs ?

Why did You choose to use PWM Regulators ?
( higher-efficiency generally costs more Money, and adds complexity )
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.
.
 

dl324

Joined Mar 30, 2015
17,122
Circuit in question:
1643486673539.png
As much as I dislike colored schematics, I left it in color because the ground line doesn't connect to where there are dotted crossings that would indicate that they do.
 

Thread Starter

Evan Moore

Joined Dec 18, 2021
8
Are You trying to get your rather strange Simulation to work,
or are You trying to design an actual Power-Supply ?

Did You use 2-Transformers because You already have them,
and want to use them for this project ?

If You already have the Transformers, what are their VA-ratings ?

Are You expecting to build this with "Junk-Drawer" or "Jelly-Bean" parts that You already have ?

A "Variable-Power-Supply", that's a very broad statement ............

What is the specific Voltage-Range that You would like to have ?

How much Current do You expect from this Power-Supply ?

Do You want adjustable Current-Limiting ?

What is Your acceptable level of Ripple on the Outputs ?

Why did You choose to use PWM Regulators ?
( higher-efficiency generally costs more Money, and adds complexity )
.
.
.
I am trying to make the simulation work, which I will then turn into the power supply, I would have used spice, but I am still new to it and I occasionally have issues importing 3rd party components, so instead I used the circuit simulation software that I used in my electrical engeneering class, which I am still used to.

I already have the transformers.

I got the transformers for the project.

I am not home, so I do not have the exact specs of the transformers on me right now.

I am buying all the parts that I need.

I want a range from 0-6V on the 6V line, 0-+30V on the +30V line, and -30-0V on the -30V line.

On any one line I expect max usage I might feasably use to be 2 Amps, and that would be a rare occurance.

I was going to add the current limiting later, and for now just use a fuse. once the circuit is complete I plan to add the current limiter.

max acceptable ripple is around .01V

I chose to regulate the voltage with PWM because I originally planned to use the LM317 and LM337 IC, but the power supply would draw an unnecicarily large amount of power when I have a low voltage, so I decided to regulate it with PWM.
 

Papabravo

Joined Feb 24, 2006
21,305
I am trying to make the simulation work, which I will then turn into the power supply, I would have used spice, but I am still new to it and I occasionally have issues importing 3rd party components, so instead I used the circuit simulation software that I used in my electrical engeneering class, which I am still used to.

I already have the transformers.

I got the transformers for the project.

I am not home, so I do not have the exact specs of the transformers on me right now.

I am buying all the parts that I need.

I want a range from 0-6V on the 6V line, 0-+30V on the +30V line, and -30-0V on the -30V line.

On any one line I expect max usage I might feasably use to be 2 Amps, and that would be a rare occurance.

I was going to add the current limiting later, and for now just use a fuse. once the circuit is complete I plan to add the current limiter.

max acceptable ripple is around .01V

I chose to regulate the voltage with PWM because I originally planned to use the LM317 and LM337 IC, but the power supply would draw an unnecicarily large amount of power when I have a low voltage, so I decided to regulate it with PWM.
If that is the case you should round up a reference book on switch mode power supplies. Trying to do this on you own is a pretty heavy lift.
Good luck.
 

LowQCab

Joined Nov 6, 2012
4,290
Here's the rub ..........
"" max acceptable ripple is around .01V ""
While this certainly can be done with Switch-Mode-Regulators,
there's quite a bit of extra Filtering-Design and Components needed for achieving those Specs.

This is a very simple Project for Linear-Regulators,
especially because it's "only" ~60-Watts per Channel.

Let us know what You decide ............
.
.
.
 

bassbindevil

Joined Jan 23, 2014
838
Numerous hobby electronics magazines have published plans for good quality power supplies over the years. AmericanRadioHistory has thousands of back issues to download (though scan quality isn't great); you may find better scans at Archive.org of particular issues. And if you venture into the murky world of warez sites, you might find torrents or direct downloads with original pdfs of more current magazines.
And I think "The Art Of Electronics" textbook has some info on power supplies; that can be found as a pdf.
 
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