Chopper

The chopper or continuous converter - continuous is a device of the electronic of power implementing one or more ordered switches and which makes it possible to modify the value of the tension of a source of continuous tension with a high Rendement. Cutting is done at a very high frequency what results in to create an average tension. It is the analog, for the sources of continuous tensions, of the Transformateur used in alternative mode.

If the tension delivered at exit is lower than the tension applied in entry, the chopper is known as reducing transformer . In the contrary case, it is known as booster . There exist choppers able to work in the two manners (Boost-Buck).

One defines the cyclic Rapport by:

For a chopper reducing transformer, the report/ratio of the output voltage on the tension of entry is equal to the cyclic report/ratio.

Certain choppers are also reversible: they can then provide energy to the load, generally a machine with D.C. current in this type of application, or take some what makes it possible to slow down the machine.

The choppers of power are used for the variation speed of the driving with D.C. current. In more low power, they are an essential component of the food to cutting. The number of revolutions of an engine with D.C. current with permanent magnets is then directly proportional to the supply voltage of the armature.

Principle of operation

It should initially be known that in electronics of power a condenser behaves like a source of tension, and an inductance like a power source.

First case: the switch is open (state " off")

The law of the meshs makes it possible to obtain the relation which follows:

$Vs\; =\; -\; Vl$ gold $Vl\; =L\; \backslash \; times\; (\backslash \; frac\; \{di\; (T)\}\{dt\})$ and it comes: $Vs\; =\; -\; L\; \backslash \; times\; (\backslash \; frac\; \{di\; (T)\}\{dt\})$

the relation thus is found: $I\; (T)\; =\; -\; Vs\; \backslash \; times\; (\backslash \; frac\; \{T\}/\{L\})\; +If$ the variation of current is thus: $I=\; \backslash \; frac\; \{(1-a)\; \backslash \; times\; (T\; \backslash \; times\; (Vs))\}\{L\}$ with T the period and has the cyclic report/ratio.

Second case: the switch is closed (state " on")

the law of the meshs becomes: $Vl=Ve-Vs=L\; \backslash \; times\; \backslash \; frac\; \{di\; (T)\}\{dt\}$ from where: $\backslash \; frac\; \{di\; (T)\}\{dt\}\; =\; \backslash \; frac\; \{Ve-Vs\}\; \{L\}$ it comes: $I\; (T)\; =\; \backslash \; frac\; \{(Ve-Vs)\; \backslash \; times\; T\}\; \{L\}\; +Io$ The variation of current is thus: $I=\; \backslash \; frac\; \{has\; \backslash \; times\; T\; \backslash \; times\; (Ve-Vs)\}\{L\}$

Relation between Ve and Vs

one a: $I=\; \backslash \; frac\; \{-\; (1-a)\; \backslash \; times\; T\; \backslash \; times\; Vs\}\; \{L\}\; and\; I=\; \backslash \; frac\; \{has\; \backslash \; times\; T\; \backslash \; times\; (Ve-Vs)\}\{L\}$

thus: $\backslash \; frac\; \{-\; (1-a)\; T\; \backslash \; times\; Vs\}\; \{L\}\; =\; \backslash \; frac\; \{has\; \backslash \; times\; T\; \backslash \; times\; (Ve-Vs)\}\{L\}$ and after some simple calculations: $Vs=a\; \backslash times\; Ve$

Let us determine the relation now binding the average current in inductance by knowing that the average current in a condenser is null.

$Il\; moy=Ir\; moy+Ic\; moy$ gold $Ic\; moy=0$ $Il\; moy=Ir\; moy$ $Il\; moy=Vs\; moy/R$ One of deduced the value from the coil to have a conduction continues i.e. the minimum current in the coil is positive (It mini>0) $Il\; mini=Il\; moy-\; \backslash \; frac\; \{I\}\; \{2\}$ $Il\; mini=\; \backslash \; frac\; \{Vs\; moy\}\; \{R\}\; -\; \backslash \; frac\; \{(1-a)\; \backslash \; times\; T\; \backslash \; times\; Vs\; moy\}\; \{2L\}$ $Il\; mini=\; \backslash \; frac\; \{Vs\; moy\; \backslash \; times\; (\backslash \; frac\; \{1\}\; \{R\}\; -\; (1-a)\; \backslash \; times\; T)\}\; \{2L\}$

However $Il\; mini\; >\; 0$ thus $\backslash \; frac\; \{Vs\; moy\; \backslash \; times\; (\backslash \; frac\; \{1\}\; \{R\}\; -\; (1-a)\; \backslash \; times\; T)\}\; \{2L\}\; >\; 0$ and it comes: $L\; >\; L\; mini=\; \backslash \; frac\; \{(1-a)\; \backslash \; times\; R\; \backslash \; times\; T\}\; \{2\}\; =\; \backslash \; frac\; \{(1-a)\; \backslash \; times\; R\}\; \{2f\}$ with $f=\; \backslash \; frac\; \{1\}\; \{T\}$

See too

• Converter Boost
• Converter Buck
• Converter Buck-Boost
• Converter Ćuk
• Converter SEPIC
• Converter Flyback

External bonds

• Choppers, forms of waves

Random links:

Mining cottage (Maine-et-Loire) | Spain of the Lights | Diocese of Nanterre | Nicola Piovani | Alain Satié | Abaissement_(hydrologie)

© 2007-2008 speedlook.com; article text available under the terms of GFDL, from fr.wikipedia.org