Hi, as you asked; "I'm intrigued by that idea (I like the multivibrator too). Could you (or someone else) maybe just sketch such a circuit so we could see what it might look like?"
I would build the "power multivibrator" like below with all the parts but not the regulator parts seen in grey.
It should be easy enough to get it running at the desired full power level into the 9v load.
So this circuit actually works! (in simulation, at least):
**broken link removed**
Sorry for messy schematic. You'll notice I added a resistor (2.2K) across the switch's base capacitor to "push" more voltage (or is that current?) through to the base. It seems to have worked.
According to LTspice:
Output voltage: 5.5V
Output current: 55 mA
Switch base drive: 0.8V (still not enough?)
The output waveforms are very choppy and chaotic (run the simulation yourself to see). But it works!
(Note: I didn't change the filename from the previous circuit, in case that matters. I'll start doing so to reduce confusion.)
Did you try the circuit i posted in post #22? That's pretty much a min parts count circuit. You'll need the output diode and cap instead of the LED.
But I really do want 9 volts, and more current if I can get it. What's holding me back here?
How much current do you want?
Do you want the 9V output of the converter to be tightly regulated, or would the regulation you would normally get from a 9V battery anyway be good enough?
Sorry, Mr Al: I didn't want you to think I was ignoring you.
Yes, I did play around with your very interesting circuit. In fact, I simulated it (.asc file below). Here's what I started with:
**broken link removed**
You'll notice I made a small change (replaced Q2 with my trusty BC337). Everything else is the same, except of course for the output capacitor and load resistor.
I took the liberty of redrawing it so it made a little more sense, at which point I could see the classic boost topology. (Sometimes it makes a difference how we draw our schematics.)
**broken link removed**
When I ran it, I got rather surprising results. First of all, I couldn't use anything larger than that 01.µF cap; it just wouldn't work with anything larger. I wondered if a decent-size capacitor is just too low-impedance a load for it?
When it worked, it seemed to want to produce ~20 volts at ~18 mA. Not too shabby. But then I took a closer look at some big spikes I noticed on the voltage plot:
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Yikes! Your circuit is a little scary. What's up with those super-spikes?
But seriously, do you think this could be tweaked to behave a little better? and maybe produce more current at a reasonable voltage (like, oh, I don't know, 9 volts)?
What kind of oscillator is that, exactly? I assume that Q1 is doing the oscillating and the other one is doing the switching.
Very interesting. I'm going to keep it around. I think I want to concentrate on my "power multivibrator", but this is definitely worth investigating.
Always a pleasureI'm actually kinda glad I didn't get any responses to those latest postings.
Well, not exactly, but basically, the circuit has 2 states, On & Off.how exactly does it work?
Hi Carbonzit you are doing good so far.
(Re above) The first thing to do is increase the inductor to about 470uH (500uH you had before). That will allow the lower operating frequency with the larger caps.
I also don't think R1 needs to be as low as 220, it only needs to be a similar value to R4, and a value of 1k will give you better energy efficiency later.
R2 is your friend, it controls the ON time period, so a pot here can quickly help you tune the duty and freq for testing.
D2 can be a cheap 1N4148, no need for special schottky diode there.
The -1.2v pulses at Q2 base should be ok.
Also you might want to re-think the amount of output current you need, if this is a "9v battery replacer" then most devices running off 9v battery are designed to only need a few mA, so 20 or 30mA max should be plenty! At least consider the option of making one circuit that works well (high efficiency) from 0mA to 30mA or even less, and if you need a high current one make a second set of values for 0mA to 100mA. There are very few things that will draw 100mA from a 9v battery!
Well, I played with it some more, and this is the best I could get:
**broken link removed**
Results as shown (Vo: 10.8V; Io: 49.1mA @ Rl = 220Ω).
Not bad. But I have to say I'm very skeptical of this circuit. Change one component--and not by very much--and it fails to start at all. I actually found best results with a plain Jane 2N2222. If someone can come up with better results I'm prepared to be beaten.
Yes, the absence of a ground may have allowed the circuit to pick up DSCSI, as you described. Funny that LTspice didn't warn me about having no ground as it usually does.
You never answered my question about the oscillator: how exactly does it work?
Do you have LTspice (or another Spice) so you can try my simulation?
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