Using a gyrator circuit instead of an inductor

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xerxesdaphat
 
Posts: 2
Joined: Mon Jul 24, 2006 1:25 am

Using a gyrator circuit instead of an inductor

Post by xerxesdaphat »

Hi there, I love your circuit, and used many ideas from it to build my own switching reg USB charger out of a National step-up boost converter instead (and Penguin mint tin instead of your weak Altoid bollocks! ^_^). Now, one thing, I'm a compsci and therefore my analogue electronics ability is somewhat lacking (although I'm reasonably familiar with digital circuitry).

As I'm not too familiar with inductors because of this, I was doing some reading up on them and noticed something about a circuit called a gyrator, which can simulate a real inductor with capacitors and an op-amp (or transistors). The article said they're commonly used in place of real inductors with ICs, as inductors are quite massive, especially when you compare to to-day's SMD tech. I thought this might be quite useful, as I had a hell of a time obtaining an inductor for my switcher, and the shipping I paid was equivalent to around ten inductors just by themselves. However, the article also said there are a few limitations, such as you can't get high Q factors, and the circuit has more resistance than a real inductor. It also said they are used mostly for quite high inductor values, such as 1 henry (and the max758 you used asks for a 22mH inductor, no?).

So my question is, is it feasible to use a gyrator circuit to replace the large, bulky, inconvenient inductor in your and other switching reg circuits?

-Tommi

adafruit
 
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Joined: Thu Apr 06, 2006 4:21 pm

Post by adafruit »

the inductor has to pass ~1A with .02 ohm resistance @ 200khz...doesnt sound like something an op-amp can handle, eh? :)

xerxesdaphat
 
Posts: 2
Joined: Mon Jul 24, 2006 1:25 am

Post by xerxesdaphat »

Heh I guess not.

After googling a little, I found this interesting paper though:

http://users.ece.gatech.edu/~rincon/pub ... d_mult.pdf

It describes using an inductor `multiplier'. It even deals specifically with switchers. It's all very academic in the paper (being a paper and all) but I might play with this and an RF inductor or something this weekend...

On another note, I have built another USB charger with another sort of switching regulator; a charge pump. I chose this because I'm looking for small size, and asking another compsci I know who programmes microcontrollers (so therefore small things which are portable ^_^) he let me know about these charge pumps which are 8-pin, SMD, and require a couple of capacitors and no inductor. There aren't many that supply enough current though, but I did find a couple that can do more than ~120mA... my one was from Microchip. Less efficient than a boost converter though.

Isn't electronics fun? Sometimes I think I'm in the wrong field heheh... I like playing with these funny little be-wired black boxes...

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