AN731

Description

Figure 1 shows a typical dc-to-dc converter configuration AN731. As in many PWM controllers, the non-inverting input of the voltage feedback error amplifier is internally connected to the reference voltage, V_r. The output voltage of the converter is set by a resistor divider network R1 and R2. This AN731 enables a fixed output voltage that is equal to or greater than the reference voltage. But in many power conversion designs, it is useful to vary the output to a value lower than the reference voltage and to dynamically adjust the output voltage. The op-amp circuit shown in Figure 3 gives designers a simple way to do this. Scaling the output voltage with respect to a control voltage V_C is totally flexible. This AN731 application note describes how to use this simple solution and provides a step-by-step design procedure to assist designers in calculating the specific parameters required by their circuits.