Hi there, I was looking to make my own power supply based on this design , a lm358 based supply http://www.mjlorton.com/bench-power-supply-project/ , There was a follow along video series, but the problem of offset voltage wasn't really resolved. I have ordered all the parts, really cheap actually components about £2 per supply minus the transformer, just something about the look of these older supplies that are really appealing.

What I was wondering is that I came across a circuit for a voltage follower / Unity gain amplifier used for offset nulling, iv attached the original circuit and one with where I think the offset circuit goes. I have replaced the 2n3055 with a TIP3055, any help would be greatly appreciated as believe it or opamps were more of a addition to a circuit, than the actual main building blocks in our electronic class's.

Also any other recommendations of parts I can order to help improve the circuit will also be appreciated.

Kind regards,
Rick

 

Welcome to AAC!

There was a follow along video series, but the problem of offset voltage wasn't really resolved.

What makes you think you'll have a problem with offset voltage?



7mV isn't going to make much difference for any practical circuit.

 

Hi denis thankyou for your reply, well in the youtube comment lots of people where talking about the leakage though the op amp, starting the circuit and having the volt meter not read zero volts. well I think that's what they where saying, so im happy you cleared that up for me, I was also wondering the comment section was also talking about decoupling capacitors for reduced noise?.

Kind regards,
Rick

 

well in the youtube comment lots of people where talking about the leakage though the op amp

What does that mean?

starting the circuit and having the volt meter not read zero volts.

Why does that matter? A power supply with an output of 0V isn't very useful.

I was also wondering the comment section was also talking about decoupling capacitors for reduced noise?

Decoupling capacitor requirement depends on the circuit. You add them in the circuit, not the power supply.

 

Hi dennis, The circuit is from this youtube web series https://www.youtube.com/playlist?list=PLDBuVMDVJaX2wCN84B5sjFMKDsMbsS7jq people comment on the videos, saying they have issues with the circuit, like leakage, feedback,noise. one commented that because of this small voltage shown at the output , with the increase in current this will increase this effect on the output. which got me worried about the circuit, so I was looking at ways to address the issues. clearly I shouldn't have listened to the comments in the video.

So im all okay to start bread boarding .
thankyou.

 

clearly I shouldn't have listened to the comments in the video

There is a lot of junk on YouTube. The animal rescue videos are interesting, but I'd've snatched myself bald if I watched/listened to YouTube videos on electronics. They take forever to make a point and all too often, they're wrong. There are some who know what they're talking about, but they're the exception.

A little ripple/noise/voltage change won't make have much impact on most circuits.

For small circuits, I breadboard on a Heathkit 3100 experimenter. The power supplies are pretty bad, but I rarely have problems.

This is the positive power supply. It has a couple hundred mV of ripple and it still doesn't cause problems with most CMOS or opamp circuits.

 

Well being born in the 90's , the new stuff was great but I was always interested in the older electronics, as they where the building blocks of the stuff to come, Heathkit 3100 , Wow, I'm jealous , looked it up, germanium transistors? , this gives me some good ideas on extras I can add to my power supply, I'm also flirting with the idea of a built in cmos logic probe, & I had the idea of a circuit that injects high or low signals into circuit, will have to experiment with what iv got ,did a quick diagram

 

Also im guessing if I use a single bicolour led instead of the two, with a high frequency signal, the led should turn orange?

 

Wow, I'm jealous , looked it up, germanium transistors? , this gives me some good ideas on extras I can add to my power supply,

Don't think they're germanium. Will check some day...

I'm also flirting with the idea of a built in cmos logic probe, & I had the idea of a circuit that injects high or low signals into circuit

A good logic probe would also indicate float conditions. I'm partial to the HP545A. There's a companion HP546A Logic Pulser. Also better than anything I could build.

Prices wax and wane, but they're usually available on eBay. I acquired my first HP545A back in the late 70's when they were still quite expensive.

 

Well being born in the 90's , the new stuff was great but I was always interested in the older electronics, as they where the building blocks of the stuff to come, Heathkit 3100 , Wow, I'm jealous , looked it up, germanium transistors? , this gives me some good ideas on extras I can add to my power supply, I'm also flirting with the idea of a built in cmos logic probe, & I had the idea of a circuit that injects high or low signals into circuit, will have to experiment with what iv got ,did a quick diagram

View attachment 170436 View attachment 170437

From offset to bicolor LEDs; wow!

Focus on the important and then go for the bell and whistles that very seldom could prove useful or esential.

 

Heathkit 3100 , Wow, I'm jealous , looked it up, germanium transistors?

All transistors are silicon: 2N4121, MPSA20, MJE171, MJE181.

 

I was going off the image you sent of the voltage regulator, 407-801 transistor, looked it up because fort I would give the circuit a go.

atferrari , I get too easily exited, I will however be breadboarding the hell out of power supply first, promise. then designing a printed circuit board. Then a couple of months down the line , having a working prototype.

Dennis , probes a good bit of kit, my main aim for the project is something functional and easily fixable , also cheap, going to use a 24v power brick with a 3a resettable fuse instead of a transformer, making the design pretty much assessable to anyone.
Here's a example of the probe, advantage is I can use it with my circuit, with no voltage regulation and the same opamp which are 50pieces for $2.

 

You can pick a 24v 96w supply for around £5, even better go to the tip and pick up a 24v printer power brick for free.

 

I was going off the image you sent of the voltage regulator, 407-801 transistor, looked it up because fort I would give the circuit a go.

These are the transistors used:

probes a good bit of kit, my main aim for the project is something functional and easily fixable

If you're going to make one, have a setting for TTL and CMOS and have some appropriate thresholds. You can do a float indication, but it takes more circuitry.

This is what the HP545A uses:


That probe also captures one shot events and slows down pulsing signals to 10Hz.

opamp which are 50 pieces for $2.

At that price, they must be counterfeit.

 

The circuit is from this youtube

How in the heck can you spend 5 or 6 hours talking about a simple power supply?

 

Here's a example of the probe

What a dumb video. How was that supposed to be helpful? It was short, but still a waste of time.