# Half-Bridge vs Buck Converter

I have some confusion regarding the difference between half-bridge and buck converters. I thought they were inherently different structures (H-Bridge having a transformer) however in some places, I've seen the term 'half-bridge buck converter' used.

Can someone clarify to me the difference?

An H-bridge is not a half-bridge. The 'H' in H-bridge is not shorthand for half-bridge. An H-bridge is formed with two half-bridges and to produce a circuit in the shape of an 'H'.

An H-bridge's only job is to allow you to take a single-polarity source and swap it's polarity across a load. That load can be a a motor, an electromagnet, a speaker, a transformer, whatever. It doesn't change the fact it is an H-bridge.

A half-bridge is two switches connected together between a power rail. It's job is to switch the node common to both switches to one rail or the other, or disconnect it from both.

A simple buck converter uses a high-side switch and a free-wheeling diode sharing a common node with the inductor.

You can increase the efficiency of a buck converter by replacing the free-wheeling diode with a low-side switch and controlling it appropriately. This removes the forward voltage drop of the free-wheeling diode. This forms a half-bridge with the high-side switch that was already there. Replacing the free-wheeling diode with a switch is also called "synchronous rectification".

simulate this circuit – Schematic created using CircuitLab

• Ah I see. In the half-bridge, the common node between the switches still isn't the output right? The output is after the inductor. Half-bridges are only step-downs as well? Commented May 22, 2021 at 2:34
• Well, the common node of the half-bridge is the output of the half-bridge. Whether or not the output of the half-bridge is the same as the output of the overall circuit is a different matter. You can do a lot of stuff with half-bridges. I wouldn't generalize to step down only. A half-bridge on its own can't stepdown either without an inductor. It just connects a node to either GND, +V, or disconnects it. Commented May 22, 2021 at 2:35
• Ohhh. So the two switches is what we are referring to as a half-bridge configuration and depending how we connect the inductor/capacitor, we can achieve a certain topology - buck, boost, etc. So when people say 'half-bridge buck converter', they really mean a synchronous buck converter with two FETs rather than a FET and a diode. Commented May 22, 2021 at 2:37
• Yes. Correct... Commented May 22, 2021 at 2:37
• Thank you very much! It all makes sense now! Commented May 22, 2021 at 2:38