There are a vast array of power supplies on the market, and the variety of resistor applications, such as high voltage resistors, anti-surge resistor, non-inductive resistors, in those designs broaden the selection dramatically.  Whatever the application, power supply designers must be aware of specific regulations on safety or the environment that apply to the area, as well as the actual electrical performance.

The nomenclature of power supplies is often taken from whether the input is AC or DC, and what type of regulation is used to provide the correct DC output – normally switched mode or linear. Mains voltages usually power AC-DC supplies, while a DC-DC supply could be powered from a battery or any other DC power source. These DC-DC converters use switched mode technology to change the input voltage to a higher (boost) or lower (buck) output voltage.


Off-the-shelf power supplies are available for many markets and for general use, but in some cases a custom design is needed. Resistor manufacturers and suppliers such as Microhm Electronics have many years of experience in helping customers choose the correct component for every application. An example of these is for switched-mode power supplies. Linear power supplies can be inefficient due to energy being expended in both the series pass device and the load. The inefficiency increases the higher the voltage drop over the load.

To drive up efficiency, another supply topology is often used. The switched-mode power supply (SMPS) takes the unregulated input DC voltage, and switches it at a high frequency (10kHz to 1MHz). The duty cycle determines the DC output voltage after rectification and smoothing.


The regulation of the SMPS output also uses a potential divider, but this time to regulate the frequency of switching and the duty cycle. The SMPS can achieve efficiencies of up to 95% by avoiding the losses from the linear regulator’s voltage drop. The SMPS can also be more compact than a similarly rated linear AC-DC supply, as the high frequency transformer and filter/reservoir capacitors are much smaller.

The main drawback for the SMPS is that it must have a minimum load. No-load conditions can damage the supply. To avoid this condition, designers often use a power resistor as a dummy load. This resistor is intended to draw the minimum specified load if the main load is detached. Naturally, the dummy resistor will dissipate power, which will have an effect on the overall supply efficiency and will need to be considered when specifying the resistor. Another way to circumvent this problem is to use a shunt resistor across the output if the load goes open circuit. Other resistors are also used in SMPS designs for safety purposes.Low-ohm, high-power resistors often protect against over-voltage conditions. Current limiting designs protect against short-circuits.

This type of switching technology is also used in DC-DC converter designs to change one value of DC voltage to another. Buck converters are very similar in operation to the SMPS design described previously. Boost converters output a higher voltage than the input using charge pump techniques. Both technologies use similar ways to regulate the output voltage and for circuit protection. High voltage resistors, HPMRY series,  EE series and NLT series are applicable to these applications.