A resistor that can handle extremes
From soft-start and snubber circuits to dynamic braking and RF dummy loads, the list of applications for non-inductive bulk ceramic resistors continues to grow as more design engineers discover the devices’ inherent advantages. Ceramic resistors are ideal for a wide range of requirements in equipment such as radar, motor drives, broadcast transmitters, RF amplifiers, semiconductor process equipment, high voltage power supplies, switchgear, x-ray, lasers, medical defibrillators, and energy research.
Sophisticated electronic equipment and systems often require rugged resistors that perform reliably under conditions involving a combination of high voltage, current, or energy. Typically, these are advanced-technology power-intense higher-cost systems, where it is critical that the resistors meet stringent requirements. Bulk ceramic resistors represent the best choice for these applications because of their many design advantages.
Pulse, pre-charge and softstart
In power supplies and motor drives, the compact pulse energy capability of ceramics allows flexible design without sacrificing power. In comparison to wire wound, ceramic resistors can obtain greater power dissipation in 1/3 of the footprint of the other material. This delivers excellent performance where high peak power or high-energy pulses must be handled in small and efficient spaces.
In high voltage situations, both continuous and pulse applications are solved with ceramic resistors. Some systems include radar, x-ray, defibrillators, lasers, broadcast transmitters and semiconductor process equipment. These systems can include crowbars, capacitor charging or discharging, and HV power supply protection circuits. In these uses, bulk ceramic resistors provide low inductance, high average power per unit size, stability at high voltage, and durability at extreme peak-power levels.
When a spike in voltage occurs from electrical switching, an RC snubber circuit is used to suppress these discharges and protect the circuit. In this instance, a wire wound or film resistor may not hold up to the high voltage, current or energy conditions. The power spike can result in megawatts of instantaneous peak power which the small mass of film or wire-wound resistors would degrade and possibly fail. Even though resistors can be used for applications like switchgear and transformer transient protection, wind power converters direct this additional energy into a safe source ultimately protecting the equipment.
Bulk ceramic resistors are used extensively for high-frequency loads in broadcast and communication equipment because of their non-inductive characteristics. They provide excellent non-inductive power-handling capacity at frequencies into the gigahertz range, with no sacrifice in power dissipation. In advanced digital applications such as digital radio and HDTV transmitters involving pulses at high frequencies, the size flexibility and unparalleled overload reliability become clear with ceramics.
It’s best to assure protection of circuits before commissioning, which is why test loads can help design against catastrophic events. High energy may be desired in a testing situation, whether that is a minor spike from an electrical circuit or diverting a lightning strike. RF antenna matching uses a compatible load to mimic the desired transmission in order to select the proper antenna. This can also be done with digital transmission, where custom engineered assemblies are a cheap insurance policy during a disaster. In the case of power generators, test loads allow for a risk free verification of the unit's capabilities.
Summary of resistor comparisons
|Non-inductive (Henry, H)||30-56000||2-200||2-200|
|Geometry size||Complex packaging||Flexible||Flexible|
|Power range||5 W to 1 kW||1 W to 1 kW||1 W to 1 kW|