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Astable multivibrator

by Crazymechanic
Tags: astable, multivibrator
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Nov29-12, 04:54 PM
P: 853
Hi I would like to know is it reasonable to make a astable multivibrator that is fed from about 325v dc , the rectified +filtered mains.?
I understand that with the right transistors and resistors I will get some oscillation but the question is will i be able to get a nice square wave to drive some mosfets that would then drive a transformer primary?
The idea is of a as simple as possible smps power supply not using any ic's or chips.
So yes the question is can such an arrangement work efficiently and smoothly enough for it to be called a reasonable smps?

I have done very much simulation before finalizing my schematic on multisim but the program is kinda weird sometimes as when I had one circuit with all the transistors and so and it worked very good the simulation showed a nice square wave. I had potentiometers set as reostats in the "r2" "r3" places so that I could tune in for the best performance.Now I calculated the resistance set on those potentiometers and made a new design with all the same just usual resistors in those places and the circuit didn't function at all even changing values was no luck.
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Nov29-12, 08:57 PM
P: 1,815
Short answer: Yes

It depends on a number of factors, however. What frequency do you want to operate at? How much current output do you need?

While there are high voltage transistors you might be better off using high voltage mosfets, tubes, SCRs, or even electro-mechanical relays.
jim hardy
Nov30-12, 12:05 AM
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does it run with R2 and R3 removed?

There's no reverse overvoltage protection for your E-B junctions,,,

but i dont know anything about multisim.

Get one running at ~6 volts with 2N3904's for proof of principle....

Nov30-12, 03:35 AM
P: 853
Astable multivibrator

well i start with getting one working with about 12 volts and yes with the 2n3904 as I already tried simulations with them in Multisim.
But the main idea stays the same building this simple multivibrator with robust high voltage transistors and feed it directly from the rectified mains then creating a square wave that would drive some mosfets ofcorse I'll include some protection.

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