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how can a buck converter be more efficient than a linear reg

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Newbie level 1
Jan 29, 2013
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Hi Am a newbie trying to understand how switch mode regulators work.

Say I wanted to convert 32v into 12v using a linear reg @1A then I would dissipate extremely large amount of heat.
But I always been told if you use a buck converter instead you dissipate less heat. On this website
Mike explains that when the the pass transistor inside the reg switches off, the ouput cap will eventually be discharged via the switching diode until
the transistor is switched on again.

My understanding:
Am I correct in saying it gives off less heat because unlike a linear regulator it doesn't drop 20v@output current
across the regulator. Instead it uses the supply voltage to trickle charge the capacitor to the desired voltage. So as long as the regulator switches off it's
pass transistor in time it'll be only be partially charged to the desired voltage. When the transistor is switched off the capacitor is discharged via the diode.
The regulator switches the pass transistor on to charge it back up. This happens at such a high frequency, the load receives a relatively stable output voltage.

Everything dissipates heat. Question is, how much (and,
if you're curious, why).

A properly designed buck converter spends almost all
of its time conducting at low voltage drop across one
switch or another. Note that on old school, high voltage
output types the "switch" may be a diode on the low
side. At any rate you're talking a volt or less @ Imax
in either state, and switching accounts for some small
fraction of the period (during which you will traverse
a region of dissipative conduction).

Meanwhile your linear has no choice but to drop all
excess voltage (@ current) as heat. Not -a- volt.
Tens or more, quite often.

Your retelling of the tech blog misses an important detail, the inductor working as energy storage. Without it, you won't be able to improve the efficiency compared to a linear regulator.

I would expect current and voltage waveform for a visual expalantion of buck converter operation.

The thread below discusses switched-coil converters.

Look for my post with a link to an animated simulation of a buck converter. With simulated scope waveforms.

It's interactive. You control the action. Click a switch to start the power cycle, then let up on it to see the second half of the cycle. This learning tool was invaluable to help me grasp an understanding of the forces at work.

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