This article describes how special converters with PassThru™ mode function when the input voltage of the circuit is too high or too low to power the load. This article shows examples of how to use step-boost regulators and boost regulators with pass-through mode to improve power supply efficiency and EMC performance.
    In some applications, the existing supply voltage can drive the load directly without the use of additional voltage converters. Sometimes, when the operating state is abnormal, the supply voltage may be too high or too low to directly power the load. In these cases, special voltage converters optimized for this operation can be used. For example, the industrial 24V system is one such application. We assume that the load requires a 24 V supply voltage, but the available 24 V input voltage sometimes increases to 38 V, or decreases to 15 V, beyond the allowable supply voltage range of the load. For these applications, a typical boost regulator or buck-boost regulator can be used.
    Figure 1 shows a schematic of the system for such an application. Portable radio devices are powered by batteries. The load can accept voltages between 10 V and 14 V, but the output range of the voltage source may be 8 V to 16 V. Then the interpolated buck-boost regulator can convert the voltage to 12 V at the output. If the supply voltage is slightly below 12 V, the converter operates in boost mode, and if the supply voltage is higher than 12 V, it operates in buck mode.