Trimming The Output Voltage Of DC/DC Converters

The simplest and least expensive solution is to connect a resistor from the VOUT Adjust pin to the minus (-) reference point or to the plus (+) reference point (positive point where the feedback RF resistor is connected. When a variable voltage source, such as a digital-to-analog converter (D/A) or OPAM, must be used for adjustment, the circuit in Figure 2 can be used. The circuit in Figure 1 is a variable current source that can be used to perform a ±10% adjustment of the converter's output voltage. The auxiliary output is preloaded by RLF and an overvoltage zener diode to prevent any overvoltage condition in case the external load is not installed or disconnected. The converter in Figure 4 is the same converter given in Figures 3A, 3B and 3C with one exception: it incorporates output synchronous rectification for its main output. The converter in Figure 4 does not need a preload for its main output due to the fact that the loop is energized by the switching loss in the MOSFETs.