Introduction to Forward Type Switched Mode Power Supply
Forward type switched mode power supply:
Fig: Basic topology of a Forward converter
- Forward converter is another popular switched mode power supply (SMPS) circuit that is used for producing isolated and controlled dc voltage from the unregulated dc input supply.
- As in the case of fly-back converter the input dc supply is often derived after rectifying (and little filtering) of the utility ac voltage.
- The forward converter, when compared with the fly-back circuit, is generally more energy efficient and is used for applications requiring little higher power output (in the range of 100 watts to 200 watts). However the circuit topology, especially the output filtering circuit is not as simple as in the fly-back converter.
- The topology of a forward converter consists of a fast switching device ‘S’ along with its control circuitry, a transformer with its primary winding connected in series with switch ‘S’ to the input supply and a rectification and filtering circuit for the transformer secondary winding.
- The load is connected across the rectified output of the transformer-secondary. The transformer used in the forward converter is desired to be an ideal transformer with no leakage fluxes, zero magnetizing current and no losses.
- The basic operation of the circuit is explained here assuming ideal circuit elements and later the non-ideal characteristics of the devices are taken care of by suitable modification in the circuit design.
- In fact, due to the presence of finite magnetizing current in a practical transformer, a tertiary winding needs to be introduced in the transformer and the circuit topology changes slightly.