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Old 5th June 2010, 12:23 AM   #1
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Default Buck converter using TL494?

This isn't related to audio, but I'm looking for a circuit using the TL494 switchmode controller to take 12 - 24 volts, and step it down to 5volts, without the need for a transformer.

I've seen all kinds of circuits, they either use a transformer, or are a boost circuit using an inductor.

All I want, is a simply buck regulator, using an inductor, not a transformer.

I'm sure its possible, but can't find one!

thankyou for your time!
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Old 5th June 2010, 12:33 AM   #2
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you can find example of buck converter in TL494 datasheet
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Old 5th June 2010, 12:35 AM   #3
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I found this... seems to be what I want, but why a transistor, not a mosfet? and whats limiting the current to only 1amp?

The inductor, for a start, but is that all?

Click the image to open in full size.
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Old 5th June 2010, 01:37 AM   #4
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They use a BJT because it's old. It's also slow (~30kHz?).

If the voltage is low (under 20V), you can use a MOSFET. Drive might be with a booster transistor, or you might use a TL598 instead (totem pole output, the rest of the circuit is identical -- but watch out for changed pins). If the supply is higher, you must limit gate voltage, perhaps with some resistors, transistors and a zener, or use an N channel FET driven with a bootstrapped driver (IR2101 style or discrete).

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Old 5th June 2010, 06:45 AM   #5
luka is offline luka  Slovenia
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Read this, really good stuff, I think I will try and done one or two

2-transistor Black Regulator
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Old 5th June 2010, 12:09 PM   #6
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Quote:
Originally Posted by luka View Post
Read this, really good stuff, I think I will try and done one or two

2-transistor Black Regulator
I like the look of those.

Might play around with them a bit, see what kinda current you can get with some bigger transistors..

but, it might just fail badly
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Old 5th June 2010, 03:51 PM   #7
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I prefer self-excited oscillators with a feedback winding, which gives much better drive than an inverting transistor. I've talked with Black; he doesn't like this approach because the additional winding isn't as "simple" (i.e., it's more that could possibly be screwed up).

Click the image to open in full size.

Click the image to open in full size.

This is a constant current source, but the basic concept could be rewired for a current-mode buck converter.

Because of the circuit's resemblance to a blocking oscillator, BCM is probably best. CCM works for CC Buck because of the feedback resistor; you don't get DC feedback through a transformer (though you can get it through two, with diodes).

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