frequency divider questions...

[11-90-an]

Isnt the jfet acting like a switch in this circuit? A bjt can be used as a switch too.. or is it about those arguments whether bjts are current or voltage controlled...

Anyhow, where do you guys buy your j201s or 2n5457s? I believe that the j113 can be replaced with these....

And of course, it's more convenient to waste our own time..!! 

Ahh love this forum...
I don't have enough experience and parts to attempt stuff like these... still have to order

[antonis]

or is it about those arguments whether bjts are current or voltage controlled...

BOTH of them are VOLTAGE controlled items (despite what many textbooks say..) but BJTs exhibit Base current "annoying imperfection"..
(they DO need current but only as operation resulting accessory..)

[duck_arse]

about the LM324 - it is meant and best for battery circuits, because it can be pulled down to ground at the inputs without complaining. the TL0xx won;t go as low at the inputs, and have restricted output voltage range, less than supply, more than 0V.

so replacing the LM324 in the rectifier section with LM358's is fine and equivalent, but TL0x2's may misbehave.

[antonis]

but TL0x2's may misbehave.

Particurally when pushed down near -Vee supply rail, it can oscillate badly..
(although, never verified it for single supply..)

[Rob Strand]

Isnt the jfet acting like a switch in this circuit? A bjt can be used as a switch too.. or is it about those arguments whether bjts are current or voltage controlled...

The BJTs' can produce a small glitch each time it switch.  That comes from two places.  The switch output, the collector,  has a DC voltage when the switch is on.    Because the DC voltage is switched off and on a cap in series with the collector won't help.  The second issue is the base current needs to be relatively high.  The base current must pass through the emitter.  The DC current on the emitter can cause further DC shifts/glitches, for example on Vref.

If you have some post filtering you might get away with it.    It's one of those things you just have to try.

[11-90-an]

If you have some post filtering you might get away with it.    It's one of those things you just have to try.

Ok.. gonna buy some parts... if i were to choose just one, what should i get? Lm324 or tl074?
I get that the tl0xx might oscillate, but how bad can it get? 

[Rob Strand]

It's up to you.  If you can use cheap parts like the LM324 then why not use those.   Boss use a TL022 which is a cheap, low performance part like an LM358.