A triangle-wave generator using discretes

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Good that it worked.

Today I felt inclined to tweaking. Now no more weird scheme; just +Vcc.

I provided my own (simpler) astable driving the switching. To get the switching working properly with a single supply I needed to reference both current sources to a point halfway between ground and Vcc (R9 & R10 divider on the right).

If the second it takes to stabilize seems too long (as you say, is not), play with R9 & R10. They control that part upon start.

My current suggestion, astable included, is simpler and works.

 

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I like it, but unfortunately it doesn't seem able to drive much of a load; it'll handle a 10KΩ load, barely, but nothing more. Oh, and I changed the integrator cap to 4.7μF.

Maybe further tweaking might improve things? Unfortunately I'm kinda over my head here, can't be of much help to you.

One thing I was wondering about is whether you really need 2 transistors to gate the current sink (Q5 & Q3); couldn't this be done with just one?
 

At the moment, I do not see how to do it with just one transistor. I will sleep on it.
 
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Those Zs, worked marvels and insomnia brought fresh ideas.



The astable now drives the switching transistor directly.

No more glitches; C4, down at the sinking source, seems to cater well for that. It would be good to see if it works OK in real HW. More if you make it variable in frequency. (Making it bigger to cover all ranges?)



Be well.
 

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If you wanted to eliminate the current mirrors .....
 

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Of course the simple circuit has a very high output impedance so it cannot drive anything except maybe an opamp. Oh, maybe an opamp should have been used to make the entire circuit in the first place.
 
audioguru said:
Of course the simple circuit has a very high output impedance so it cannot drive anything except maybe an opamp. Oh, maybe an opamp should have been used to make the entire circuit in the first place.
Click to expand...
Yes, it may be a interesting academic exercise to design such a circuit with discrete devices but you can do it with many fewer parts along with better performance using op amps.
 
alec_t said:
If you wanted to eliminate the current mirrors .....
View attachment 89752
Click to expand...

I like it very much. For simplicity alone it should probably win the prize in this thread.

So, how does it perform? I modeled it with my multivibrator. It works pretty well.



Notice, however, how the waveform degrades with increasing load (decreasing load impedance). It seems to be able to drive about 20KΩ adequately. If one were to add a couple stages of amplification (a high-Z input CE amp plus an emitter follower, perhaps), one might make a pretty decent function generator out of it. (These are for 20K, 5k and 1K loads resp.)





Annoyingly, I had to modify the astable to get it to work with LTspice (by changing transistors and by adding a little "startup" capacitor). Dunno why it wouldn't start here when the same circuit starts elsewhere ...
 

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I think even a poor man would be better off using opamps rather than discrete transistor cicuitry .
 
Did you check out that link I gave above? It was about a square-wave generator someone made literally in a war zone, using only available parts.
 
Yes, I checked it. A multi-range multivibrator with an R/C differentiator.
made literally in a war zone, using only available parts.
Click to expand...
A pretty good parts selection for a war zone! I think real ingenuity was shown by POWs in WW2, who made radio receivers from little more than rusty razor blades and the odd scrap of scavenged wire.
 
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