User`s guide

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Software Design

3.4 SECONDARY SIDE CONTROL SOFTWARE (DC_DC)

3.4.1 Single-Phase Buck Converter

3.4.1.1 SINGLE-PHASE BUCK CONVERTER CONTROL SCHEME

The Single-Phase Buck Converter on the SMPS AC/DC Reference Design uses peak

current mode control. The control scheme is shown in Figure 3-10.

The control loop is implemented by utilizing the analog comparator module. The Buck

MOSFET current is sensed using a current transformer and fed directly to the analog

comparator input.

FIGURE 3-10: SINGLE-PHASE BUCK CONVERTER CONTROL SCHEME

The measured output voltage is compared with the reference to produce the voltage

error. The voltage error compensator is then executed and a current reference value is

obtained. The current control loop is implemented on the dsPIC DSC using the analog

comparator by varying the programmable threshold in software.

The analog comparators on the dsPIC33FJ16GS504 have built-in programmable

Digital-to-Analog Converters (DACs) that determine the comparator threshold. The

calculated current reference is used to set a new threshold for the analog comparator.

When the inductor current signal exceeds the programmed threshold, the comparator

terminates the PWM pulse. This termination of the PWM pulse effectively modifies the

ON time for the PWM signal to control the output voltage.

The Voltage Error Compensator is implemented as a PI function in the ADC ISR.

3.4.1.2 SINGLE-PHASE BUCK CONVERTER IMPLEMENTATION USING THE

dsPIC DSC

The resources used on the secondary side dsPIC DSC for the Single-Phase Buck

Converter are summarized in Table 3-4.

TABLE 3-4: dsPIC

DSC RESOURCE ALLOCATION FOR SINGLE-PHASE

BUCK CONVERTER

Voltage

Reference

OUT

Buck

Inductor

Voltage Feedback

PWM

Buck

Current

Sense

OUT

Sense

Voltage Error

Compensator

ADC

1001011011

S&H

Analog

Comparator

REF

Calculated

Current

Reference

Current-Limit

Shutdown

Description Type of Signal dsPIC

DSC Resource Used

Buck Current Analog Comparator Input CMP1A, AN0

Buck Voltage (V

OUT) Analog Input AN1

Single-Phase Synchronous

Buck Gate Drive

Drive Output PWM4H, PWM4L