Boost converter
The boost converter also boost converter or step-up regulator , English boost converter or step-up converter is in the electronics , a form of a DC-DC converter . The magnitude of the output voltage U A is always greater than the magnitude of the input voltage U E .
Layout and function
An inductance ( coil ) L is connected in series with a freewheeling diode D , behind which a charging capacitor C adds up the output voltage. The coil is switched to ground by a suitable switch (e.g. MOSFET , GTO thyristor or a transistor ). At the coil now the input voltage drops U E from the current through the coil and thus the magnetic field stored energy increase. If the switch is opened, the coil tries to maintain the flow of current. The voltage at its secondary end rises very quickly until it exceeds the voltage U A applied to the capacitor C and the diode opens. At first, the current continues to flow unchanged and continues to charge the capacitor. The magnetic field is broken down and releases its energy by driving the current through the diode into the charging capacitor and to the load.
properties
The output voltage of the step-up 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 nor 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 this exceeds a certain minimum value). Nevertheless, the pulse width is often modulated by a control circuit, especially if the output voltage is to be variable or the current is to be regulated (for example with chargers). Boost converters can be used well to generate a higher output voltage or to regulate a strongly fluctuating input voltage.
Application examples
The basic circuit of a step-up converter is used in DC-DC converters whose input voltage is lower than the output voltage, e.g. B .:
- battery-powered devices connected to one or a few cells work
- Generation of 24 V from a 12 V car battery
- Control of common rail injectors
- Generation of 400 V from 12 V with capacitor ignition
- Operation of several light-emitting diodes on a single battery cell
- DC voltage side of inverters in photovoltaic systems
The same principle, but with a transformer instead of the coil, is used in low-power switched-mode power supplies (so-called flyback converters ). (Strictly speaking, this is not a transformer, but a choke with two windings. In the case of a transformer, the input power consumed is output at the same time. )
The circuit is also in PFC (Engl. Power Factor Correction for power factor correction used) input stages, the internally an intermediate circuit voltage of 400 V DC power supply. The power consumption of these PFC stages is adjusted to the sinusoidal curve of the input voltage, so that contamination of the network by harmonics is avoided. Switching power supplies, frequency converters or electronic ballasts, which would otherwise generate strong harmonics , then work on this intermediate circuit voltage.
generalization
If, in the circuit diagram above, the diode D is replaced by a further switch S 2 , together with the control logic required for the correct timing, it becomes the synchronous converter . The name is derived from the necessary, correct time control of the switches, which takes place in a similar way to synchronous rectifiers . The synchronous converter can then be converted directly into a step-down converter by swapping the input and output and represents the generalization of the step-down and step-up converter in the topology.
