A forward converter is a device in which power moves from the input side of an electrical circuit to the output end in a single direction. It is a type of switched mode power supply circuit, used with unregulated direct current (DC) input power supplies, that contains a core, transformer, and switch in its most basic form. Energy is not held in the transformer when the switch is conducting, as it is in a flyback converter, and the device itself is also more energy efficient. Used in DC to DC conversion systems designed for under 100 watts of power, the forward converter, derived from buck and boost converter designs of the 1920s, was first created in the mid-1950s.
Most electrical converters transfer power when turned on, and have a constant rate in which their on and off states are switched. The frequency of the switching is controlled by pulse width modulation. This characteristic of the forward converter switch varies with the flow coming through the input, and at the same time the on state of the switch controls the electrical output. Longer on times should mean better efficiency, but also cause the reset voltage to go up which negatively affects how the converter performs. Designers have to also consider the switch voltage and current as well as how the switch reacts to high frequencies.
An important characteristic of the forward converter is that current does not flow between different segments linked by one conductor. Charges also will not pass from the device to a person touching it, so this galvanic isolation makes the converter safe to use as well as an efficient means to convert electrical currents. The converter’s transformer has metallic wire windings that conduct electricity at the same time but have opposing magneto motive forces. Conflicting forces in the primary and secondary windings help regulate the magnetic flux so sudden changes in energy level don’t cause power surges.
Trapped energy is further regulated in a forward converter by a third winding, through which current is conducted to mitigate the rise in energy levels. When used for higher electrical voltages, the converters have primary and tertiary windings that are wound together for more efficient transfer of electromagnetic energy. Overall, the design of the forward converter has remained the same over the years. The ability to improve the design and construct smaller circuits, however, has enabled engineers to build converters with switching frequencies exceeding 500 kilohertz.
By Andrew Kirmayer