Forward converter
Encyclopedia
The forward converter is a DC/DC converter that uses transformer
windings to buck or boost the voltage (depending on the transformer ratio) and provide galvanic isolation
for the load. It performs the same operation as the flyback converter
, but is generally more energy efficient.
For comparison, a flyback converter stores energy as a magnetic field in an inductor airgap during the time the converter switching element (transistor) is conducting. When the switch turns off, the stored magnetic field collapses and the energy is transferred to the output of the flyback converter as electric current. In contrast the forward converter (which is based on a transformer) does not store energy during the conduction time of the switching element - transformers cannot store a significant amount of energy unlike inductors. Instead, energy is passed directly to the output of the forward converter by transformer action during the switch conduction phase.
The use of a transformer in the forward converter also constrains the maximum output voltage to the transformer turns ratio, 'n'.
The transfer function is:
where 'D' is the pulse width modulator duty cycle and 'n' is the transformer turns ratio,
The forward converter is used to provide a higher power output (100–200 watt
s).
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
windings to buck or boost the voltage (depending on the transformer ratio) and provide galvanic isolation
Galvanic isolation
Galvanic isolation is a principle of isolating functional sections of electrical systems, thus preventing the movement of charge-carrying particles from one section to another, i.e. no direct current flows between the sections. Energy or information can still be exchanged between the sections by...
for the load. It performs the same operation as the flyback converter
Flyback converter
The flyback converter is used in both AC/DC and DC/DC conversion with galvanic isolation between the input and any outputs. More precisely, the flyback converter is a buck-boost converter with the inductor split to form a transformer, so that the voltage ratios are multiplied with an additional...
, but is generally more energy efficient.
For comparison, a flyback converter stores energy as a magnetic field in an inductor airgap during the time the converter switching element (transistor) is conducting. When the switch turns off, the stored magnetic field collapses and the energy is transferred to the output of the flyback converter as electric current. In contrast the forward converter (which is based on a transformer) does not store energy during the conduction time of the switching element - transformers cannot store a significant amount of energy unlike inductors. Instead, energy is passed directly to the output of the forward converter by transformer action during the switch conduction phase.
The use of a transformer in the forward converter also constrains the maximum output voltage to the transformer turns ratio, 'n'.
The transfer function is:
where 'D' is the pulse width modulator duty cycle and 'n' is the transformer turns ratio,
The forward converter is used to provide a higher power output (100–200 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s).