Precision through-hole resistor connects to secondary side of current-sensing transformers

21-01-2015 | Vishay Precision Group | Passives

Vishay Precision Group (VPG) VFR has introduced a new high-precision Bulk Metal Foil Burden through-hole resistor. Designed for connection to the secondary-side of current sensing transformers, the device offers low TCR down to ±0.2ppm/C from -55C to +125C, 25C ref., and high load-life stability of ±0.005% after 2,000 hours at 0.1W at 70C. Current sensing transformers act as current sources and require a load. Like a voltage source, a current source shouldn’t be left open, as it would cause an infinite voltage. The VFR Burden resistor converts the current to a limited voltage. Typically, the device will be used to discharge a capacitor when the circuit is no longer powered. The Burden resistor is usually connected to the output of the power device for the discharging of the bulk output filter capacitor when it is charged and connected to a large power source, such as an accumulator or airplane battery. The resistor offers a low resistance of only a few ohms and prevents the influence of inrush current to the device to which the power unit is connected. Inrush currents usually happen when the battery or accumulators are very large and their capacitance is too high. The resistor offers a maximum power rating of 0.6W at +70C. The device features a resistance range from 1ohm to 500ohm, with tight resistance tolerance to ±0.005% (50ppm). Any conceivable ohmic value within this range, to six digits, is available with no additional cost or lead time effect. The resistor withstands ESD spikes to at least 25kV and is available with both lead (Pb)-free and tin/lead alloy termination finishes. Samples and production quantities are available, says the company.

By Craig Dyball