Electronics notes/Changing voltage

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This is for beginners and very much by a beginner. It's meant to try to cover hobbyist needs, and as a starting point to find out which may be the relevant details for you, not for definitive information.

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See also Category:Electronics.


When you talk about trying to get an particular voltage level, 'voltage regulator' and 'voltage converter' are near-synonymous terms, and 'voltage stabilizer' is also related.


Some terms and properties

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)
  • Step-down: output voltage is lower than the input voltage
  • Step-up: output voltage is higher than the input voltage
  • Inverting - Creates a voltage of opposite polarity
(Not to be confused with 'inverter' , which refers to DC-to-AC conversion, such as those use in cars, and solar panels that provide AC power)


  • Charge pumps - designs that use capacitors for temporary storage, switching it one of a few ways to exchange voltage for current (fractionally divide/multiply one for the other)
Charge pumps are somewhat cheaper and simpler than inductor-based circuits.
Depending on design and use, they may be ~80-95% efficient, usually a bit less.


  • low-dropout, often referring to voltage regulation step of something larger:
A low-dropout variant requires less input-output voltage difference than is typical.
e.g. where linear regulators often need 2 to 2.5V higher input, LDO regulators may need only 1.5V.
note that they are often also pickier about what range they comfortably accept
Can matter for small drops, for efficiency, for battery-powered situations


Continuous/Discontinuous mode:

  • Discontinuous designs either simply discharge to zero, or rely on a short-term buffer to sustain current (e.g. capacitors)
Discontinuous designs are often simpler and smaller.
  • Continuous mode never discharge too significantly during operation (which particularly for DC-DC converters depends on load), meaning you'll always get current.
Performance is usually better in continuous mode.



Further notes:

  • In any designs that are based on feedback, stability and adaptation speed are conflicting interests.
  • One distinction is whether you use a switching design (stepdown can e.g. be primarily resistive instead)

LED drivers

LED drivers are often CC (Constant Current) or CV (Constant Voltage) - see also Electronics_notes/Diodes#LED_drivers

DC-to-DC

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Shunt regulator

A shunt regulator is based on a (zener) diode used as a shunt. [1]. Upside: very simple Downside: low current capacity, and requires a fixed design, zener burning out puts full voltage on output


Transistor series regulator

A transistor series regulator is basically a shunt regulator fed into a transistor as a voltage follower[2].

Upside:

  • Better regulation than shunt (transistor's base is a light load)
  • handles more current

Downsides:

  • still sensitive to load variation, sensitive to supply variation.
  • Linear regulator is often better for similar price.

Linear regulator

So the more typical resistive design is the linear regulator,

  • basically operates as a variable resistor, intentionally wastes the voltage difference (times the current actually drawn) as heat
  • named for being a device (BJT, FET, tube) operating in its linear region - or passive device like a zener diode operating in its breakdown region.
...and contrasted to e.g. switching regulators
  • Simple, cheap
  • lower noise than switching (still has thermal noise) particularly for lower frequencies


Fixed versus variable linear regulators:

  • you can change a fixed, but variable ones are more precise (and efficient) to tweak

Low-dropout regulator (LDO)

  • a (typically linear) regulator which can work with a lower-than-typical voltage difference
  • More power-efficient (than basic linear) for larger currents
  • sometimes a practical necessity (over linear) when supply voltage is not far away (consider e.g. batteries)


Around the regulator:

  • you'll want a capacitor on the input side, particularly if it's a bit away from the power supply
on the order of ≥0.1 μF or more on the input side (verify)
but too large will make it less stable (verify)
  • a capacitor on the output side can help stability and transient response
could be on the order of ≥1 μF (verify)


See also:

Switching designs

Switching designs refer broadly to any design that uses fast switching to change how storage elements (inductors and/or capacitors) are connected, and can be step-up, step-down, and inverting constructions..

Since they work with a charge-discharge cycle they will have voltage ripple in their output.

Efficiency (often something between 70% and 90%) varies with current drawn, so are typically more efficient than linear regulators (except in some low-difference situations, where LDOs may actually be more efficient).

See also:


Designs of switch-mode regulators include:

Step-down

Buck converter

a switch-mode step-down design, based on a single inductor



http://en.wikipedia.org/wiki/Buck_converter

Step-up

Boost converter

a switch-mode, step-up design, based on a single inductor

Basically charges a capacitor, and connects it so that it regularly doubles the input voltage

http://en.wikipedia.org/wiki/Boost_converter

Step-up or step-down

Buck-boost converter

(Note: distinct from the buck / boost transformer)


based on a single inductor

(inverting)

mostly used for stabilisation

http://en.wikipedia.org/wiki/Buck-Boost

flyback converter

basically buck-boost, but with the inductor split into a transformer

giving isolation, and allowing voltage multiplication via the transformer

can also do AC-to-DC

Push-Pull converter

(similar to the flyback converter)

http://en.wikipedia.org/wiki/Push–pull_converter

Forward converter

http://en.wikipedia.org/wiki/Forward_converter

Split-Pi

topology of inductors and capacitors

similar to buck-boost

http://en.wikipedia.org/wiki/Split-pi

Ćuk

inductors and capacitors(verify)

http://en.wikipedia.org/wiki/%C4%86uk_converter

SEPIC

Single-ended primary-inductor converter

inductors and capacitors(verify)

https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter


DC level shifting

AC-to-DC

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Half-Bridge rectifier

https://en.wikipedia.org/wiki/Rectifier#Half-wave_rectification

Full-Bridge rectifier

https://en.wikipedia.org/wiki/Rectifier#Full-wave_rectification


AC-to-AC

transformer

The basic transformer can be seen as a specific exchange between voltage and current.

Flyback transformer

Zeta converter

buck / boost transformer

(note: distinct from the Buck-boost converter)


capacitive dropper

DC-to-AC

Inverter

Basically anything that generates a simple waveform, and allows load worth mentioning to be drawn from it.

http://en.wikipedia.org/wiki/Inverter_%28electrical%29

Other

See also

Comparison notes

Transformer notes

Named purposes / designs

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


On cores, on windings, on taps

Going from transformer to DC, design considerations

Rectifying AC

Could I reverse primary and secondary?

Can I series-connect for higher voltages?

Can I add more transformers in parallel later for more current?

Unsorted