Question

Multisim buck converter. Looking for an example for 5A, 3-36V to 1.25-32V. Need to be able to build in multisim 12z

Answer 1

Multisim buck converter

The buck converter is a form of power switch which dramatically increases the efficiency of the regulator circuit. Its core functionality is built upon switching a voltage to control the output voltage allowing us to step down the input voltage to that needed by the output. A capacitor is required to smooth the output voltage and remove the steps created by the switching

To achieve this, a Pulse Width Modulated (PWM) signal is used to control the switching of the voltage allowing regulation of the output voltage. When the switch is closed, the inductor will begin to charge and there will be a voltage drop across it causing the output voltage to drop. When the switch is open, the charge within the inductor is released, supplying the output voltage.

Below is an example of a simple Buck Converter. A PWM signal is being used to control the switch, allowing the charge in the inductor to build up. Care needs to be taken when selecting the most suited frequency for the PWM signal in order to maintain the required DC voltage level.

To help with determining the correct frequency and component values, Multisim provides interactive components which are capable of having their parameters changed during execution. The use of interactive components allows us to adjust the duty cycle, impedance and resistance during simulation.

The example above shows an open loop implementation of a buck converter. This can be taken a stage further and translated into a closed loop system by taking the output voltage and comparing it to a reference voltage to produce the appropriate PWM signal for the switch.

This can be fully modelled in Multisim alongside LabVIEW using co simulation.

Multisim gives you the tools to simulate a schematic prior to the circuit creation whilst LabVIEW assists in creation of the FPGA code. Co-simulation allows these two systems to be integrated allowing full testing of the power switch prior to deployment.