Managing PWM Waveforms - Buck Converter

To demonstrate data reduction in a PWM design I've copied and modified Mike Donnelly's Buck DC to DC Converter at

I've added a simplified softstart to simulate startup. Sofstart is implemented by ramping up internal voltages over a 5ms period after a 0.5ms delay for a total startup time of 5.5ms. Mike's load transient is timed to activate after steady state. A line transient can be simulated by adding a pulsed voltage source in series with v_line.

The total time to simulate startup, steady state and the load transient is set to 10.5ms of which only the final 4ms involve the response to the transient disturbance. Downloaded .csv files of the output voltage (v_out_buck), inductor current (l1inductor/i), or any other signal cover over 84,000 time points.

For a 40us switching cycle, a 1us resolution samples each switching cycle 40 times and requires only 4,000 time points to cover the steady state and load transient response. A voltage source is included in the design to mark off this sampling resolution with a sawtooth signal that starts at 6.5ms. The sawtooth appears at the net named x_smpl. Downloading x_smpl along with v_out_buck to Excel enables edits that reduce the original 84,000 time points to 4,000.

To demonstrate the data reduction technique for large .csv downloads,t he design includes a dedicated table voltage source which has been preloaded with a set of 4,000 samples from an earlier simulation. The voltage signal vout_reduced displays those 4,000 samples. The table voltage source can be edited to insert to store reduced data records of any transient response generated by this buck converter.

Copies of the table voltage source can be placed into this or any other design in order to display the transient response or apply it to another simulation. This mechanism can be used to test designs that are driven by the buck converter output for their ability to withstand the transient disturbance. Other simulations can be used to compare the simulated response to measured data or to analyze the simulated transient response.

Watch for an accompanying blog that will explain how the table voltage source works.

Norm's picture




Joined April 18, 2016
Design added Tuesday, August 8, 2017 | 11:11 pm PDT