Soft switching converters

Hard-Switching is simply forcing the transistor to turn on and off commutate by adding the current or voltage to the third pin to enable the changed states. Hard switched transistors in large wind turbines and electric trains are designed to be pulled out of the system and be replaced as a form of maintenance.

Hard switching is easy to understand and therefore is used almost universally in power converters outside of the low power DC to DC space. Hard switching is thought to be low-cost because only a limited number of other components are required to drive the transistors between states.

In reality, hard-switching is expensive at the system level and inefficient. Hard-Switching has numerous well-known drawbacks, the largest of which is the introduction of switching losses. Power converters using Hard-Switching again, virtually all of them , need to balance the desire for higher switching frequencies with the need for acceptable system losses to meet the desired system efficiencies.

In practice this means that systems requiring high efficiencies are designed to switch slowly to gain efficiency. The efficiency gains come from reducing the cumulative amount of switching cycles and hence cumulative switching losses of each transistor in the conversion process. By slower switching frequencies produce high harmonic distortion and output ripple. Distortions and ripple generally need to be filtered to make the power usable.

Power designers typically solve this problem by adding larger output filters -which again adds cost, size and weight. Hard-Switching artificially limits the maximum switching frequency at which transistors can be commutated switched on and off. Each transistor has a limit of the amount of heat it can dissipate.

This maximum thermal dissipation must be balanced between conduction losses and switching losses for the desired outcome. Increasing the switching frequencies to reduce the size of a system means that the transistor has to carry less working current to accommodate the higher switching losses. This can be solved by adding a larger transistor with less conduction losses —but this also adds costs to the system. In short, with hard-switching, the switching losses generated by switching faster means less conduction losses can be accommodated.

Without the losses hard switching creates, transistors would be free to switch much faster or handle more current for the same thermal limit. The key take-away is that Hard-Switching transistors yields inefficient systems with increased cost, size and weight.

His idea was to use an external circuit to prevent overlap of the voltage and current wave forms during transistor commutation. Today, there are two types of soft switching: a self-resonant and b forced resonant.

In self-resonant Soft-Switching, a self-oscillating circuit is used to precisely time transistor commutation, resulting in the offset of the current and voltage wave forms Figure 4. The benefits of a self-resonant Soft-Switching topology is the elimination of switching losses, an increase in efficiency and the reduction of EMI. The main drawback of self-resonant Soft-Switching is that the architecture only works in non-isolated power converters when input voltage and output loads stay within a narrow range.

Forced-resonant soft switching topologies use numerous inputs input voltage, load, transistor voltages, currents etc. Skip to main content. This service is more advanced with JavaScript available. Advertisement Hide. Soft-Switching dc-dc Converters. Chapter First Online: 24 December This is a preview of subscription content, log in to check access. Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window Open image in new window.

Issa Batarseh 1 Ahmad Harb 2 1. German Jordanian University Amman Jordan. Personalised recommendations. Cite chapter How to cite? ENW EndNote.