Technical Information Site of Power Supply Design

2021.09.29 Simulation

# Summary

Optimization of PFC Circuits

In the previous articles we have explained how to deal with changes in the various conditions of a PFC circuit, and have used five examples involving study of important parameters and the like to explain adjustment methods and related points. In circuit design and revision tasks, when modifying conditions and evaluating the modifications, hardware must be employed to supplement desktop calculations. However, evaluations using hardware not only incur time and expenses, they may not be feasible under some conditions. For these reasons, circuit simulations are without any doubt a useful tool for design and evaluation activities. Ultimately, evaluations using actual equipment are indispensable, but simulations are advantageous for reducing the time and man-hours leading up to this.
Below are links and key points for each of the sections of this chapter. They should prove useful for detailed analysis.

Introduction

## Key Points:

・The ROHM Solution Simulator is a web-based simulation tool that can be used simply by registering on MyROHM.

・Solution Circuits for simulation of circuit operation are provided in the ROHM Solution Simulator.

・Solution Circuits currently exist in two categories, Power Device Solution Circuits and ICs Solution Circuit

PFC Simulation Circuits Using Solution Circuits

## Key Points:

・The ROHM Solution Simulator web page features various information relating to simulations, and different simulations can be run.

・When a product is being considered for use, upon going to the product page, a simulation circuit that can be used immediately can be accessed.

## Key Points:

・An example is shown in which, when operating conditions are changed in a PFC CCM circuit, the inductance current ripple ratio is corrected by adjusting the inductance.

・An inductance resulting in an appropriate ripple ratio is calculated, and a simulation is performed to verify the result.

PFC Circuits: Adjustment of Switching Frequency

## Key Points:

・An example is given in which, when operating conditions are changed in a PFC Synchronous CCM circuit, the possibility of improving efficiency while maintaining an appropriate inductor current ripple ratio by adjusting the switching frequency is studied.

・A switching frequency resulting in an appropriate ripple ratio is calculated, and a simulation is performed to verify the result.

PFC Circuits: Examination of Appropriate Gate Driving Voltages

## Key Points:

・When a SiC MOSFET is used as a switching element, because the change in Ron with changes in the gate driving voltage VGS is considerable, the VGS setting is important.

・When studying the gate driving voltage VGS of a SiC MOSFET, a balance between efficiency and safety should be considered.

PFC Circuits: Changing the Gate Resistance

## Key Points:

・When the gate resistance of a switching element is increased, noise is suppressed, but there is a tradeoff with reduced efficiency. Hence it is extremely important that the gate resistance be set so as to achieve a balance.

・Simulations can be used to determine the maximum value of the gate resistance RG when holding switching element losses to below a specific value.

PFC Circuits: Examination of Optimum Dead Time Values

## Key Points:

・The dead time settings in a bridge circuit are related to losses and safety, and so must be studied thoroughly.

・The optimum value for the dead time is the shortest time at which a shoot-through current does not occur.

・The switching speed of a switching element varies depending on such factors as the temperature and variation in the manufacturing lot, and so a margin must be added to this shortest time in the design stage.