![]() ![]() ![]() When the FET switch is opened (OFF), the magnetic field collapses and no additional current flows to the primary or secondary.During this portion of the cycle, current in both the primary and secondary is ramping up over time. This immediately creates a magnetic field that couples to the secondary winding. When the FET switch (SW) is closed (ON), the DC source is connected and current travels through the transformer primary.The basic single-switch forward cycle includes the following portions: N sec / N pri = N2 / N1 = transformer secondary to primary turns ratio Various combinations of turns ratios and duty cycles can be used to achieve the required output voltage according to this equation: The switch (SW) is commonly a MOSFET, but is occasionally a bipolar transistor and sometimes GaN or SiC. The forward-mode controller opens and closes the switch with the appropriate duty cycle to achieve the required output voltage. Typical Single Switch Forward Mode Converter Schematicįorward converters are basically buck converters that use a forward-mode transformer for isolation. Ideally, the forward-mode transformer has high (primary) magnetizing inductance, which serves to minimize the magnetizing current. Flyback transformers require a specific magnetizing inductance and have a gapped-core construction, which allows high energy storage without saturating the core. This is different from flyback topology, in which energy is stored in the magnetic field of the transformer during the first half of the conduction cycle and then released to the secondary winding(s) connected to the load in the second half of the cycle. Instead, the primary and secondary conduct simultaneously (and directly) when the switch is on, and energy is processed directly through the transformer. The core is not used for energy storage in forward-mode transformers. This article discusses forward-mode transformers and applications for which Coilcraft forward-mode transformers are best suited. Forward-mode transformers are attractive because they allow you to achieve efficiencies up to 95 – 97%. The forward-mode topology is preferred for high output power levels up to about 300 Watts, although you can use two-switch forward-mode topologies power levels down to a few watts. Forward mode includes simple forward converters as well as half-bridge, full-bridge, and active-clamp types.įorward-mode converters are used for output current requirements up to approximately 15 Amps, or when high efficiency is required. Typical Forward-Mode Transformer Current Waveformsįorward-mode transformers, also known as forward-converter transformers, transformers for forward- mode topology, or simply forwards, are used to provide circuit isolation and voltage transformation in forward-mode DC-DC converters. ![]()
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