Understanding Electronics Basics #1

[KeepItSimpleStupid]

Ratch:
Capacitors are frequency dependent ..."

poor choice of words.

What I was trying to say and did not do very well, was that higher frequency circuit designs USUALLY use need lower values of capacitance.

Low capacitance values are used in DC power supplies and even AC supplies to "bypass" high frequencies to ground. sometimes to make a high frequency oscillator could require smaller values of capacitance.

 

[cowboybob]

Graham,

We're going to make a modification to the sine wave generator you've constructed by powering it from a single 12 VDC battery (get the drift here?), amplify its output and then run that output through the rectifying/filtering network you've also constructed: DC to AC to DC.

Now, understand that there are, obviously, way[/B better, more sophisticated and smaller circuits to do this, but we're gonna use what we've already got.

This approach is called "proof of concept" confirmation.

This is going to be fun...

CBB

 

[Muttley600]

Cool, let me have a go in the morning before you give the game away
Sounds like fun

Night CBB

 

[KeepItSimpleStupid]

An interesting electronics term: Magic Smoke http://catb.org/~esr/jargon/html/M/magic-smoke.html

 

[cowboybob]

AHAH!! I knew it.

That explains SOOOOOO much...

 

[Muttley600]

An interesting electronics term: Magic Smoke http://catb.org/~esr/jargon/html/M/magic-smoke.html

**broken link removed** bet I could make magic smoke easier than I could get my head around this
I have tried four times to get a wave off a single opamp & I have now mastered crashing Tina **broken link removed**

Need to get ready for work again, this may turn out to be quite a long process getting this sim working without the math behind it, I didn't know you could upset a computer program, I must of, Tina doesnt like me anymore **broken link removed**

 

[cowboybob]

I was a able to crash TINA by giving a resistor a zero value, which, best I can tell, probably resulted in a division by zero.

ANYTHING divided by zero results in infinity. This causes a "loop" in the coding of the program which irrevocably causes a crash.

Kind of surprising they (the TINA creators) didn't code in protection against that sort of user error.

I by no means claim that TINA is the best sim, just the one I'm most familiar with. Any computer program can (and will, if properly screwed with) crash.

 

[Muttley600]

It was while playing with values that it crashed, I really need to start understanding properly instead of using Tina to do the job for me by trail & error.lol

 

[cowboybob]

It was while playing with values that it crashed, I really need to start understanding properly instead of using Tina to do the job for me by trail & error.lol

Don't feel bad. I do it all the time.

I'm still struggling to find and/or create a single transistor sine wave generator. There are tons of examples out there, but none of them work in the sim. the example I lifted from National Semiconductor (the two OpAmp job) is the only one that seems to work reliably.

 

[Muttley600]

Oh, I didn't realise we could cheat & look for one, I just kept playing with different designs hoping one would work

Ever the optimist.lol

I can get a ripple with zenners back to back on one opamp but not a wave.

May e KISS or Ratch could give us a clue

I think it's prob the zenner that needs changing, I even tried the ones we used but don't know if I'm honest

 

[KeepItSimpleStupid]

Try fig 3 here: https://en.wikipedia.org/wiki/Colpitts_oscillator Note the 50 MHz operating frequency.

 

[Muttley600]

So what frequecy would I ideally be looking at for my power supply KISS?

 

[cowboybob]

Graham,

There's a nice, relatively simple OpAmp example in TINA TI.

Go to;

File: Open Examples...: Oscillators: 1kHz Phase- Shift Oscillator.

It works fine. And it has a fair explanation of what's going on in the circuit.

KISS: Tried that one and it worked. Was able to get the freq down to about 1kHz. Where I ran into a problem was amplifying the output (and isolating it as I did that) to allow a reasonable load (the rectifying circuit, etc).

Unfortunately, I lost the TINA file of it. I'll recreate it and post a pic of what I'm talking about.

Need a second pair of eyes for this one.

CBB

 

[cowboybob]

OK. Here ya go.

View attachment 62059

Notice that I changed C1 & C2 to 1uf, and swapped R3 (10kΩ) with a 100nf cap (C4, this brought it back into oscillation).

Also changed L1 to 500mH, all of which got the freq down to about 300Hz (or so).

Whaddaya tink?

 

[Muttley600]

There's a nice, relatively simple OpAmp example in TINA TI.

Just been playing with that, although I got a wave, take 2nd battery out & it's as flat as a dodo

 

[cowboybob]

Just been playing with that, although I got a wave, take 2nd battery out & it's as flat as a dodo

No. It won't work with just the one battery.

Try the one in post 294. One battery (12VDC!!), a simple transistor, nothing weird.

This one is called a "Colpitts" oscillator.

Read KISS's post at top of this page (#291) and then the ones after.

Hang in there. This is all part of the process of getting back to the original "reverse engineered" PCB.

 

[Muttley600]

Saw KISS's post & saw the sums, they are giving us the answers for working out......
But how do you know what frequency you need to build things at?
I know you need to keep away from certain ones, but what then, build something & hope it doesn't interfer with anything? Or is it that because everything in UK or America is either 50/60htz, that's what you choose.....I'm left confused yet again.lol

Nother night over, see yer tomorrow

 

[KeepItSimpleStupid]

Whatever frequency you need as long as it doesn't get out of the box very far. Certain frequencies, in the US anyway don't carry any information and therefore don't require a license. I worked on a 1000 W RF transmitter used for sputtering. The frequency that microwave ovens operate at also don't have any information attached to it.

 

[cowboybob]

OK. Here's a circuit that works.

It's oscillating at about 300Hz with about 7VDC output (with about a 70mV AC ripple).

It can be improved upon...

View attachment 62078

Let me know what you think.

It's probably too low a frequency: the ripple might express itself as an audio distortion. Probably 25khZ might be better. Won't be heard and isn't anywhere near a broadcast issue.

Not the prettiest sine wave ever (but who cares), and the DC portion could obviously be improved. Current capacity is so-so, but an amp would take care of that.

Not so bad for a single transistor DC-AC-DC rig...

 

[Muttley600]

Morning CBB
25khZ sounds good then

ok, heres my wave but for the life of me, I can't get graph to show volts on left hand side **broken link removed**

View attachment 62079

Time to go to work again, where does the time go?