4.1 Hardware

Direct Peak Current Mode Control has been implemented on one phase of the Low Voltage ILLC development board. Although this board was originally designed for Average Current Mode Control, the rectifiers were removed from the Primary Current Sense Transformer to enable Direct Peak Current Mode operation.

The peak detect and hold circuit is essentially a differential amplifier with a voltage offset. The output of this differential amplifier is rectified and charges the capacitor during the high-side switch’s ON period.

When the high-side switch is turned off and the low-side switch is activated, the capacitor is discharged via a MOSFET. This MOSFET is controlled by the same drive pulse that operates the low-side switch on the primary side.

The gain of the differential amplifier and the voltage offset on its non-inverting input are determined by the gain of the current transformer, the current range and the burden resistor used. These parameters directly influence the DAC range over which the switching frequency can be regulated.

It is important to configure the RC network at the output of the differential amplifier to ensure the capacitor can be fully charged during the high-side switch’s ON time. Additionally, the differential amplifier must be capable of driving the output capacitor effectively. Microchip’s MIC920 operational amplifier is an excellent choice for this application, as it is well-suited for high-frequency operation.