Clueless A-stable multivibrator ?????????

[JAMES IRVINE]

Well I completely stuck with the explanation of this circuit as an a-stable multivibrator **broken link removed** can anyone tell me if the explanation in the link is relevent for the IC SN7400. I can see the top half of the layout is identical to the bottom half and that is where my understanding ends. I have been reading a book called Higher Electrical Engineering by J sheperd,AH morton & L F spence and I've found an a-stable multivibrator on page 737 that looks pretty similar to this diagram https://www.aaroncake.net/circuits/inverter.asp I've learned its junk but is it in theory an a-stable multivibrator. The Book quotes a a stable multivibrator as"two RC coupled stages are given 100 percent feedback and this gives rise to conduction process wherby one stage is fully conducting while the other is switched off, conduction being transferred from one stage to the other by the discharge of a capacitor through a resistor" does anyone have a simple answer to what is happening at the left hand end of the circuit in the first link. Am I missing the simplicity of it?

 

[blueroomelectronics]

10W is a pretty weedy inverter, why not just buy a modern HF one?

 

[Papabravo]

FYI. The correct terminology is "astable multivibrator"
The meaning of "astable" is "no stable state"
The meaning of "multivibrator" is "oscillator"

It is a fancy term for a "square wave oscillator" and the description is largely correct.

Also FYI, the other types of multivibrator are:

1. monostable multivibrator -- one stable state, also known as a one-shot
2. bistable multivibrator -- two stable states, also known as a flip-flop

 

[audioguru]

Don't try Aaron Cake's inverter.
Its capacitors have backwards polarity so they blow up.
The transistors have avalanche breakdown.
The base current for the transistors is far too low.
The small power from the transistors goes to blowing up the capacitors and heating the transistors, not to the output.

If the capacitors are reversed so they have the correct polarity then the high current from the avalanching transistors also blows them up.

 

[JAMES IRVINE]

Thankyou papabravo for pointing out the importance of the mono and bistable multivibrator.
I was wondering if you could walk me through the route of the current going through SN7400 Uncle Scrooge. I mean can you explain what is happening it cannot be the same as in the link on the same page to the astable IC multivibrator **broken link removed** because its laid out differently.

 

[audioguru]

Hi James,
I haven't seen an old SN7400 IC for about 30 years. I think a CD4047 oscillator IC is good in an inverter.

 

[JAMES IRVINE]

The thing is uncle scrooge for my project I must have two possible circuits, I have one that I can explain but need another. I could use aaran cakes as an example but I was thinking that if I used one like in the link **broken link removed** I could explain the advantages of using mosfets like in the one I will be using over using transistors. One thing about Aaran cakes I dont really understand is what is the purpose of the two diodes. If you could tell me that then I can use it. Or is there another you know of that I could use?

 

[audioguru]

There are hundreds of ways to make a multivibrator oscillator for an inverter. You need only two of them all.

The two diodes in Aaron Cake's inverter reduce voltage spikes caused by the inductance of the transformer.

 

[JAMES IRVINE]

Thanks for the info. You are probably correct not to help me cheat, its not vital for me to know about it but I've been trying some simulation software I have downloaded SwCADIII and APLAC both of which I havnt had the time to work out how to work yet.

Has anyone any links to free electronics workbench or similar user friendly simulation software?