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Basics
2.4.1
Flyback Converter
Flyback converters enable wide distribution of "low" power. Up to now, flyback converters
have only been used in power supply units with up to 200 W, approximately. Thanks to
more powerful components with reduced power dissipation, flyback converters can now be
used for power supply units with an output power of up to 1000 W, approximately.
Flyback converters are categorized according to the number of power switches used. Up
to 200 W, flyback converters require one power switch. Up to 1000 W, each flyback
converter uses two power switches.
Flyback converters consist of a smaller number of components than forward converters.
For this reason, devices with flyback converters have a light and small design and operate
particularly reliable.
Therefore, all QUINT POWER, MINI POWER and STEP POWER power supply units from
Phoenix Contact are designed as flyback converters. They cover a performance range
from 15 W to 960 W.
Method of Operation
Figure 2-12 shows the simplified structure of a flyback converter with one power switch.
The power switch S1 is switched on and off by means of a controller with the control
voltage Uctrl. The value of the output voltage Uout depends on the winding factor of the
transformer Tr and the pulse duty factor of switch S1. The value of the output voltage Uout
is continuously measured and transmitted to the controller. In this way, a stabilized output
voltage Uout is generated.
Because of the switching process the energy transport in the flyback converter is carried
out in two steps. For easier understanding, the procedures are illustrated in two different
graphics.
Figure 2-12 shows the circuit with switch S1 closed. During this operating cycle an amount
of energy is taken from the supplying network and stored in the transformer Tr.
Figure 2-13 shows the circuit with switch S1 opened. The energy stored in the transformer
is passed on to the secondary circuit.
The corresponding characteristic curves of the voltage and current are shown in
Figure 2-14.
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PHOENIX CONTACT
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