Voltage stabilization

In electrical engineering and electronics, voltage stabilization is understood as stabilizing, i.e. keeping the electrical voltage constant despite the variable current.

The stabilization of voltages is necessary when using electrical components and electronic components that require stable voltages of 5 V, for example. Simple electrical circuits , for example the supply of commercially available incandescent lamps, can certainly allow voltage fluctuations, but with highly integrated circuits (ICs) such as processors , even small voltage fluctuations can lead to malfunction or failure of the components.

Forms and application

In general, such measures are used in the already mentioned sensitive electronic circuits. Such strengthening agents are also necessary if large currents arise briefly, such as when using larger inductive loads such as motors or the like ( inrush current ).

With DC voltage, electrical components such as capacitors, Zener diodes or voltage regulators are used .

Parameters

Stabilization factors

The stabilization factors characterize the influence of the circuit on fluctuations in the original voltage . ${\ displaystyle U_ {0}}$

The voltage stabilization works better, the larger the stabilization factor and the smaller the internal resistance . ${\ displaystyle r _ {\ mathrm {i}}}$

Absolutely

The absolute stabilization factor or smoothing factor is defined as:

{\ displaystyle G = g = {\ frac {\ Delta U_ {0}} {\ Delta U _ {\ mathrm {a}}}}}

(at nominal load ).

Relative

The relative stabilization factor is:

{\ displaystyle {\ begin {aligned} S & = {\ frac {\ frac {\ Delta U_ {0}} {U_ {0}}} {\ frac {\ Delta U _ {\ mathrm {a}}} {U_ { \ mathrm {a}}}}} & = {\ frac {\ Delta U_ {0}} {\ Delta U _ {\ mathrm {a}}}} {\ frac {U _ {\ mathrm {a}}} {U_ {0}}} & = G \ cdot {\ frac {U _ {\ mathrm {a}}} {U_ {0}}} \ end {aligned}}}

(at nominal load ).

Internal resistance

The internal resistance is calculated according to:

{\ displaystyle r _ {\ mathrm {i}} = {\ frac {\ Delta U _ {\ mathrm {a}}} {\ Delta I _ {\ mathrm {L}}}}}

for .

{\ displaystyle U_ {0} = {\ text {constant}}}

Smooth

Production of direct voltage
above: Sinusoidal alternating voltage
below: pulsating direct voltage after one-way or two-way rectification

“Smoothing” is the term used to describe the conversion of a pulsating DC voltage, such as that generated during rectification, into a DC voltage that is as constant as possible.

Smoothing is often achieved by capacitors ( smoothing capacitors ) connected in parallel to the source of the pulsating voltage (rectifier). With a sufficiently high capacity , they can hold a lot of charge. As soon as the voltage drops, the stored charge can be released again without the voltage dropping too much. They thus have a buffering effect on the connected voltage source. In spite of this, the resulting DC voltage is often not yet completely free of AC voltage components; one speaks of residual ripple ( ripple voltage ). Full-wave rectification has the advantage that the frequency is doubled and therefore the filter effort is reduced.

Chokes are also used to smooth the voltage even further . They are switched into the current path ( series connection ). Because their inductance counteracts current fluctuations, they help to further reduce the residual ripple and thus smooth the output voltage. Weight and volume are disadvantageous.

Zener diodes can be used to limit voltages that exceed their breakdown voltage. You can also reduce the ripple. Zener diodes must always be operated together with a current limiter (e.g. a series resistor) at which the voltage fluctuations drop. The further smoothed (and reduced) voltage is taken off parallel to the Zener diode.

Important: Z-diodes can only reduce residual ripple by eliminating overvoltage, they cannot compensate for undervoltage. That is why they can only be used for stresses that have already been pre-smoothed.

The use of electronic voltage stabilizers has established itself as a particularly effective method for smoothing. These are connected directly to the charging capacitor and greatly reduce the residual ripple. Electronic voltage stabilizers are available in large numbers and types: fixed voltage regulators , regulators for small and large currents and also with adjustable output voltage.

Smoothing factor

See: absolute stabilization factor !

seven

Sieving is often seen as synonymous with smoothing - see also: smoothing capacitor . But it can also mean the separation of alternating voltages (currents) of very different frequency filter circuits .

The removal of high-frequency interference voltages on a low-frequency (mains) voltage is often referred to as screening.

The aim here can be to prevent radio frequency interference from entering a device (receiver). The reverse case also occurs. The connections of a switched-mode power supply are usually provided with "filter elements" which are intended to prevent high-frequency interference voltages from escaping from the device.

Typical filter circuits are designed as low-pass filters.

Filter circuits typically operate over a wide range of frequencies and are not very selective. They are supposed to suppress or "filter out" a wide frequency band (frequency mixture).

In contrast, there are narrow-band filter circuits (resonant circuits, band filters, etc.) that are used to filter a certain frequency (a transmitter) from several frequencies (radio signals). The filtered signals are usually amplified for further processing ( amplification ).

Sieve factor

The sieve factor indicates how many times greater the ripple voltage (ripple voltage) is at the input of the filter element than at the output : ${\ displaystyle s}$ ${\ displaystyle U _ {\ mathrm {w} \, 1} = U _ {\ mathrm {Br} \, 1}}$ ${\ displaystyle U _ {\ mathrm {w} \, 2} = U _ {\ mathrm {Br} \, 2}}$

{\ displaystyle s = {\ frac {U _ {\ mathrm {w} \, 1}} {U _ {\ mathrm {w} \, 2}}} = {\ frac {U _ {\ mathrm {Br} \, 1 }} {U _ {\ mathrm {Br} \, 2}}} \ ,.}

literature

Adolf J. Schwab: Electrical energy systems - generation, transport, transmission and distribution of electrical energy . Springer Verlag 2006, ISBN 3-540-29664-6 .
Klaus Beuth and Wolfgang Schmusch: Electronics 3. Basic circuits . 10th expanded edition. Vogel-Fachbuch, Würzburg 1990, ISBN 3-8023-0555-8 . Pp. 45-50 + pp. 188-209 (448 pp.).

Web links

Electronics compendium: