Buck converter using TL494?

[ThyDntWntMusic]

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!

[busan]

you can find example of buck converter in TL494 datasheet

[ThyDntWntMusic]

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?

[Sch3mat1c]

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).

Tim

[luka]

Read this, really good stuff, I think I will try and done one or two

2-transistor Black Regulator

[ThyDntWntMusic]

Originally Posted by luka

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

[Sch3mat1c]

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).





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).

Tim