Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [buck]

A non-isolated DC-DC converter topology which outputs voltage less than or equal to the input voltage

A buck converter is a non-isolated DC-DC converter topology used to step down voltage. It is one of the most fundamental converter topologies in existence.

The basic buck converter power train is comprised of a switch (usually a MOSFET or transistor), an inductor, a diode, and a capacitor.

Public-domain buck converter image from Wikipedia

The duty cycle of the switch determines the ratio of load voltage to supply voltage:

$ \frac{V_{out}}{V_{in}} \mbox = D $

An improvement on the buck converter is the synchronous buck converter, where the diode is replaced with another switch. This increases the efficiency of the converter but requires more complicated control.

Wikipedia: Buck converter

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Why do smaller loads require larger inductors in buck regulators?

The MC34063 Application Note lists the equation for calculating minimum inductor size as follows: $$L_{min} = \frac{V_{in} - V_{sat} - V_{out}}{I_{pk}(switch)} t_{on}$$ But this implies that as Ipk(switch) (eg, the maximum switch current) decreases,…
Nick Johnson
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Why would a buck converter IC fail and blow up?

I have a deployed design in which we are experiencing a high (~4%) failure rate in the 12V to 5V step-down buck converter portion of the PCB. The buck converter's role in the circuit is to step down 12 V input (from a connected lead acid battery)…
macdonaldtomw
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Why do buck (step-down) switching regulators require an inductor and diode?

So, I understand, at least at a basic level, the method of operation of switching converters, both buck and boost. What puzzles me, though, is why buck converters in particular aren't simpler. Why not build a buck converter as a switch that charges…
Nick Johnson
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Is it ok to connect the output of buck regulator in parallel?

I am using MCP16322 buck regulator powered from 12V and outputs 5V and 2A. Is it ok to connect the output of two of these in parallel? Does connecting the outputs in parallel mess up the maximum capacitance values on the output of the regulators? Is…
lyassa
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How important is self-resonant frequency for an inductor when used in a fast (~3MHz) buck SMPS?

I'm using the LM2734Z, a 3 MHz buck regulator. It's really fast which means it has a small inductor. One of the things I'm wondering is how important is the self-resonant frequency of the inductor? I'm using it to step 4.8V to 20V down to 3.3V…
Thomas O
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For a small Vin-Vout difference, is it worth using an LDO vs a buck regulator?

I want to step down 5V to 3.3V at around 250mA. As far as I see it, there are two options to consider: Buck: more space, higher cost LDO: less space, lower cost, more difficult to remove heat(?), less efficient(?) What I am wondering is will the…
Thomas O
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What is the difference between a linear regulator and an LDO

Can someone tell me what the difference between linear regulators and LDOs is? From what I have read and understood, it is that linear regulators and LDOs don't use switching elements, but I think they are the same basically. Is there something that…
user220456
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How do I select the correct inductor value for the following buck regulator?

First of all, I suck a bit at math, and I'm no electronics genius, so the stuff I do is for fun and for learning purposes... I'm working on a buck converter circuit to convert my USB Vbus 5V to 3.3V. I've selected the AP5100 and finding it quite…
josef.van.niekerk
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Where do the oscillations on the output voltage of my buck converter come from?

I am currently building a buck converter. Its main parameters are the following: 24V input 5V/3A output Able to sustain large load transient currents caused by the switching of power LEDs (~2A) I selected a synchronous buck converter from TI which…
Bat_AAAAAHHH
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Noise problem with buck/boost switching regulator

I am designing a electrical device for a research project (I'm a PhD student, but unfortunately not EE!). More info on the device can be found at http://iridia.ulb.ac.be/supp/IridiaSupp2012-002/ The last prototype had a problem with the power…
arnuschky
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High current buck converter has excessive ringing and poor regulation

I am designing a power supply to power two fiber-coupled diode arrays for a solid state laser. The diode arrays need a current controlled source of about 50 A and will have a voltage drop of < 2.2 V. The diode wavelengths drift with temperature so I…
Brian Pepin
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Low side N-Mosfet buck converter

I often see schematics of basic buck converters. The majority of these schematics use a P-MOSFET as high side switch. Why is this design preferred over a low side, N-MOSFET buck converter? simulate this circuit – Schematic created using…
Francesco
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Is it better to boost or buck?

I'm making a solder fume extractor from an old PC fan (4-pin PWM), driven by a mid-range PIC. The fan needs 12V @ max 0.28A for power and a 5V PWM @ max 5mA to control the RPM. So I'll be running the PIC at 5V and therefore I will need both 5V and…
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What is the purpose of using MOSFET instead of free-wheeling diode in Buck topology?

(Source) I usually see Buck circuit models in which a MOSFET is used instead of a free-wheeling diode. What I understand from the Buck topology is, when the upper MOSFET is off, it doesn't matter whether the lower one is on or off since the current…
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Routing a buck/boost DC/DC converter

I need some help with the layout of a power supply. I botched the first two iterations as I do not have the necessary experience, and I would like to avoid another costly run. For the sake of completeness, here is the previous (related)…
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