Boost converter
The boost converter also boost converter, boost converter english, english Step-Up Converter or Boost, is a form of electronic DC-DC converter. The magnitude of the output voltage UA is always greater than the magnitude of the input voltage UE.
Design and function
An inductor ( coil) L is connected in series with the freewheeling diode D, behind which a charging capacitor C summing the output voltage. The coil is connected through an appropriate switch ( for example, MOSFET, GTO thyristor or a transistor ) to ground. The coil now the input voltage UE, the current drops and the coil so that the stored energy in the magnetic field increases. When the switch is opened, the spool attempts to maintain the current flow. The voltage at its secondary end rises very rapidly until it exceeds the applied voltage across the capacitor C UA and opens the diode. The current flows in the first moment continue unchanged and charges the capacitor to continue. The magnetic field is reduced and thereby emits its energy by driving the current via the diode to the storage capacitor and the load.
Properties
The output voltage of the boost converter is always greater than the input voltage ( in contrast to the step-down converter ). The circuit is ( in its simplest construction) neither short-circuit or open-circuit proof, but both can be ensured by additional circuitry. In principle, the output voltage is independent of the load current ( as long as it exceeds a certain minimum value). Yet often, the pulse width is modulated by a control circuit, particularly if the output voltage variable or the current is to be controlled (for example, battery chargers ). Boost converter can be used well to produce a higher output voltage or auszuregeln a strongly fluctuating input voltage.
Application Examples
The basic circuit of a boost converter is used in DC-DC converters, the input voltage is lower than the output voltage, for example:
- Battery-powered devices that operate on one or a few cells
- Generation of 24 V from a 12 V car battery
- Control of Common Rail injectors
- Generation of 400 V from 12 V at a condenser ignition
- Operating a plurality of LEDs on a single battery cell
- DC side of inverters for photovoltaic plants
The same principle, but with a transformer in place of the coil is used in switching power supplies of low power (so-called fly-back converter ). Taken ( Specifically, it is in this case not a transformer, but a choke with two windings. During transformer the absorbed input power is delivered at the same time at the output. During flyback converter, the power and release the throttle is done through the windings in different cycles. )
The circuit is also used in PFC ( Power Factor Correction Sheet for Power Factor Correction) input stages, the device internally a DC link voltage of 400 V DC voltage supply. The current consumption of the PFC stage is the sine of the input voltage readjusted so that contamination of the network are avoided by harmonics. Then work switching power supplies, inverters or electronic ballasts, which would otherwise generate strong harmonics at this intermediate circuit voltage.
Generalization
If the diode D is replaced in the above circuit diagram of a further switch S2, including the control logic required for the correct timing control, it is the synchronous converter. The name is derived from the necessary, correct time control of the switch, which is similar to synchronous rectifiers. The synchronous converter can then be converted by swapping input and output directly to a down converter and notes in the topology of the generalization of the downward and upward converter are