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Questions tagged [switch-mode-power-supply]

A switch-mode power supply (SMPS) switches been fully-on and fully-off states quickly to maintain voltage regulation. They offer lower power dissipation and run cooler than linear regulators that continually dissipate power through a transistor.

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52
votes
13answers
11k views

What kind of components in a computer power supply can explode loudly?

Today I heard a loud bang that tripped the circuit breaker in my server room. It must have been really loud because I could hear it 2 rooms away through 2 heavy doors and it was like a firecracker ...
50
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3answers
60k views

What is the ideal way to handle data pins D+ and D- on a USB power adapter to be compatible with fast charging on devices?

I have found that many USB wall chargers use a resistive voltage divider to set the D+ and D- pins to a specific voltage, usually between 2 and 3 volts. Other USB wall chargers short the D+ and D- ...
48
votes
3answers
23k views

What does the Y capacitor in a SMPS do?

It seems that a well-designed SMPS has a capacitor connecting the ground planes of the primary and secondary sides of the transformer, such as the C13 capacitor here. What is the purpose of this ...
37
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6answers
37k views

Can an audio circuit be powered by a switched-mode power supply?

Most audio circuits are powered with large, heavy transformers and a small ripple after smoothing. SMPS are smaller and more efficient. EMI can be shielded by a metal enclosure and the output filtered ...
27
votes
4answers
18k views

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(...
26
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4answers
3k views

Spacecraft Power Supply Frequency

I know that aircraft sometimes employ a 400Hz AC system to save weight on transformers, so I'd imagine that spacecraft might employ a similar technique. I'm wondering if anyone in the aerospace field ...
26
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1answer
2k views

Unusual chemical reaction on PCB (SMPS circuit)

I have a PCB with smps circuit on it 220V to 5V (using Viper22a). Here is the schematic: And here is the board layout: In the yellow circle region, I am seeing some sort of white deposition in a few ...
22
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6answers
4k views

What are some common/popular/go-to switching voltage regulators? [closed]

So I've used the popular linear regulators (7805, LM317, LD1117, etc), but I'd like to learn more about switching regulators. Are there any "must have" switching regulators out there that are as ...
21
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6answers
26k views

Can the noise of any switching PSU be attenuated if I put linear regulator before the output?

A friend told me that noise of any switching PSU can be attenuated if I put linear regulator before output. Is that true? For example, if I want to power a +-12 V op-amp for an amplifier, I can ...
19
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2answers
1k views

How does this wall-wart switcher work?

UPDATE I've provided a full outcome report in one of the answers below with an updated schematic and description of the operating principles as I've come to understand it. I'm studying switching ...
18
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2answers
3k views

Why did they use ultrafast diodes in a 50 or 60 Hz bridge?

This is again from an HP power supply (PSU). The incoming 230 V is rectified into 340 VDC and is fed to a switched-mode supply. The odd thing here is that the manual for that unit, HP6023A, ...
18
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2answers
20k views

What might be the cause of high pitch sound coming from a switching regulator circuit

We designed a switching regulator circuit using a 1.5Mhz, internal-switch, switching regulator (semtech.com/images/datasheet/sc185.pdf). Vin is 5V, Vout is 3V3. We have an input capacitor (47uf), an ...
17
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2answers
13k views

Why is a lower switching frequency more efficient?

I'm designing a 10V to 3.3V step-down converter. Looking at the LT8610, the applications example shows two similar circuits that have different switching frequencies. The Efficiency vs Frequency plot ...
16
votes
1answer
14k views

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'...
16
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6answers
50k views

How to safely ground a switching power supply with floating outputs?

I just received a 120VAC to 5VDC (20A) switching power supply (the kind with a passively ventilated metal casing) for use with a microcontroller project I'm working on (driving long LED strips). I've ...
15
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3answers
416 views

Maximal operational pressure of tantalum and electrolytic capacitors

I need to design a device that have to operate in an high pressure environment (Nitrogen gas). The operational pressure may vary from 1bar (atmospheric) up to 20..30bar gauge pressure. The regular ...
15
votes
1answer
1k views

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 ...
15
votes
1answer
2k views

Unconventional voltage regulation scheme in the secondary of an ATX power supply, how does it work?

The regulation scheme for the +3.3 V output in this ATX power supply schematic caught my eye as strange. I just saw the schematic online, I do not actually have the physical unit. Close-up on the ...
14
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6answers
12k views

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 ...
14
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3answers
2k views

LM2586 - Inductor Heats Then Burns

I'm designing a step-up constant current source to drive LED strips (nominal load voltage is about 54 VDC). Requirements: Vin: 18..32 VDC Iout = 0.2 A Vout = 54 VDC (nominal) - 57 VDC (maximum) ...
14
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1answer
929 views

What does a black bar across transformer symbol designate?

What does a black bar across a transformer symbol designate? This appears in a power electronics context, and in particular in this case with substituting a DC transformer as an equivalent circuit ...
13
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3answers
15k views

Why is my simple boost converter giving me such a high peak output voltage?

I am trying to understand switch-mode power supply fundamentals through a simulation in LTSpice. I wanted to build an excruciatingly simple boost converter circuit following a teaching model often ...
13
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2answers
2k views

What is the purpose of copper planes in a switching power supply?

I'm looking at including a buck converter to power a 3.3V microcontroller, and I used TI's Power Designer to generate a recommended layout for my parameters. I noticed that the copper planes are ...
12
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3answers
2k views

Why is the PCB so large on this SMPS?

In a post regarding heat dissipation in a linear regulator, one answer provided this nice little pin-equivalent smps. It was a great reply, and I'll likely order a few myself. I am wondering though, ...
12
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6answers
3k views

Best way to power a microcontroller, SMPS vs Linear Regulator

I'm using a 12V adapter and a 2S 7.4V Li-ion battery to power my electronics, and I would also like to power my MCU with it. To switch between the adapter and battery I'm using a BQ24133 from TI. I ...
12
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2answers
1k views

Why do oscilloscopes use SMPSes instead of linear power supplies?

I'm wondering why digital oscilloscopes are using switching power supplies instead of linear power supplies. The SMPS has a higher efficiency, but it can produce some noise during high frequency ...
12
votes
3answers
12k views

How to choose a inductor for a buck regulator circuit?

I am designing a buck-regulator circuit, with possibly the MAX16974 as the regulator. I have never done such a thing before, and actually not too much analog electronics at all. I got stuck at the ...
12
votes
4answers
9k views

Why is flyback air gap needed for energy storage?

Why do so many sources say something along the lines "since a flyback transformer stores energy, an air gap is needed"? I have seen this reasoning in textbooks and app notes. I thought air gaps ...
12
votes
3answers
24k views

What can cause a Drain-Source short in a FET?

Background: I am using a Si7456CDP N-channel MOSFET in a switching power supply. The power supply and load are housed in a plastic enclosure. Yesterday, the power supply and load were working ...
12
votes
2answers
4k views

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 ...
12
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4answers
4k views

A 1USD 11W led bulb circuit and parts analysis

I know this is not a huge deal, but still I want to do it because for Three reasons: 1, it only costs 1 usd. Yep, this is a very cheap led bulb, and I need to take it apart to see if it's trust worthy....
12
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1answer
2k views

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 ...
11
votes
4answers
4k views

How do phone chargers have variable input voltage with constant output voltage?

My basic understanding is that a transformer can step down a voltage by the ratio of the primary and secondary windings, since this is a ratio the output is not constant. Thus my question is, how ...
11
votes
3answers
992 views

Why are boost/buck converters never fully integrated/all-in-one?

Moving from small arduino applications to higher-power applications for work, I've had to switch from using simple linear regulators to switching boost/buck converters any time a different voltage to ...
11
votes
3answers
3k views

What is the role of the diode D1 in this ramp generator circuit?

The circuit below is a ramp generator used in switched power supplies to generate a saw-tooth signal for compensation, but I don't really understand what is the role of the diode D1 in the circuit ?? ...
11
votes
1answer
2k views

Why do some switching regulator require tantalum or electrolytic capacitors instead of ceramic?

I'm looking at this switching regulator: http://www.ti.com/lit/ds/symlink/lm2675.pdf. For its input and output capacitors it recommends tantalum or electrolytic capacitors. It mentions in section 9.2....
11
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4answers
2k views

Why do we clock Buck Converters?

Apologies if this has already been asked, but I couldn't easily find an answer. So - We all know the basic design of a buck converter: Closed-loop clocked PWM into a low-pass filter. But my ...
11
votes
3answers
3k views

Minimum Switching Frequencies in Boost Converters

Why are switching frequencies for boost converters above the 100kHz range? If I understand correctly, as the frequency increases from 100kHz upwards, the ripple current that is created from the ...
11
votes
4answers
5k views

Why are charge pumps only used for low current applications?

Typically the most expensive (and hard to get) elements in a SMPS are the inductors. Thus I was wondering if it's possible to use inductor-less switching mode power supplies (i.e. charge pumps) for ...
11
votes
4answers
5k views

What are the effective power limitations of the flyback converter topology, and why?

Looking at several different isolated converter topologies, flyback looks like it's the simplest at first glance. There's only one switch, so there's only one driver, which (all other things being ...
11
votes
5answers
645 views

Pebbles in potted electronics

I was recently taking a look at a failed power supply for 12V halogen lighting and noticed an unusual texture in the potting compound. I tried chipping some of it away with a screwdriver and got a ...
10
votes
4answers
3k views

What is the maximum voltage that silicon can handle?

Today, in a race for efficiency, we have moved from transformers to switching power supplies. Almost all PSUs were designed for single-phase low-voltage operation (220Vac/310Vdc in my country). I've ...
10
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2answers
6k views

Are typical computer power supply units leading or lagging power?

Computer power supplies often have "power factor correction" features which raise the power factor in use to levels close to resistive loads (1). I'm curious what, in the absence of power factor ...
10
votes
2answers
6k views

Saturation current of my inductor not agreeing with formulas

I have wound my first inductor and I have verified the inductance with 2 methods. However, when I test its saturation current, its much lower than the formula gave me: \$B_{peak} = \dfrac{V\cdot T_{...
10
votes
2answers
1k views

Can connecting of AC adaptor first into device, then into mains pose a risk of voltage spike?

Manuals of several various electronic devices I came across recommend connecting their AC adaptor first into the device, then into mains. I always thought the reverse order is safer because I thought ...
10
votes
1answer
7k views

Hand winding smps transformer

I would like to hand wind a smps transformer for prototyping work. The specs of the transformer are as follows : Transformer Parameters Core Material: EE16, NC-2H or equivalent, gapped for ALG of 88....
10
votes
2answers
2k views

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 ...
10
votes
3answers
726 views

What causes this knee in my MOSFET drain voltage drop?

FINAL UPDATE: Understand a previously mysterious power MOSFET switching waveform wiggle! @Mario uncovered the root cause here below, distinctive to so-called VDMOS devices, typical of many power ...
10
votes
3answers
687 views

Seeking advice on resistors in switching power supply

I am trying to repair the power supply in an LCD monitor. It is a fairly basic design around an OB2268AP in the 20-30 Watt range. The power supply had failed spectacularly because the main MOSFET ...
10
votes
1answer
720 views

Why do capacitors across my FETs minimize ringing/distortion?

I'm designing a 24V to 350V DC-DC Converter based on a H-Bridge. The power requirement is 500W and the circuit operates at 20KHz. The design works fairly well and I've achieved about 90% efficiency at ...