VPG Releases Improved Bulk Metal Power Current Sensing Resistors With 3 A and 15 A Maximum Current, TCR to ±15 ppm/°C, Resistive Tolerance to ±0.1%, and Four Leads for a Kelvin Connection

The VCS101 and VCS401 offer power ratings of 1 W at +25°C and a 15 A and 3 A maximum current, respectively, while the VCS103 features a 1.5 W power rating and 15 A maximum current. All devices feature a resistance range from 0.005 Ω to 0.25 Ω. Vishay Foil resistors are not restricted to standard values, and specific as required values (e.g. 0.123 Ω vs. 0.1 Ω) can be supplied at no extra cost or delivery.

The devices released today feature a maximum operating temperature of +175°C, a rise time of 1.0 ns, with effectively no ringing, thermal EMF of 0.1 μV/°C typical, and a voltage coefficient of < 0.1 ppm/V. The VCS101, VCS103, and VCS401 offer a non-inductive, non-capacitive design to minimize hot spots.

Typical end for the resistors will include battery chargers, current regulators, dc-to-dc converters, electronic scales, motor controls, power tools, power supplies, pressure sensors, and voltage regulators in military/aerospace, medical, and industrial applications.

The need to measure the flow of current in electronic systems is becoming increasingly widespread. Reasons for this include the growth of portable, battery-powered products, which increase the need to minimize energy usage and improve efficiency. The drive for more features and less frequent recharging has led to lithium-ion, with its superior energy density, becoming the preferred technology. The task of charging a lithium-ion battery is, however, more demanding than for earlier types. This has given rise to the development of charger controller ICs, which regulate the current and voltage within the tight limits required.

There are two problems traditionally associated with using a resistor to measure current: temperature sensitivity at high currents and long thermal stabilization time when power changes. Vishay Foil Resistors' current sensing devices tackle both of these problems. Current sensing is best achieved with a Kelvin connection, as featured with the VCS101, VCS103, and VCS401, which removes the unwanted influences of lead resistance and lead sensitivity to temperature. A Kelvin connection reduces, especially for low ohmic resistance values, measurement errors due to the resistance of the lead wires and the solder joints as the sensing is performed inside the resistor, in or close to the active resistive element.

Of the commonly used methods of measuring the magnitude of electrical current, this current sensing resistor method provides the most precise measurement. According to Ohm's law, V = IR, the voltage drop measured across a resistor is proportional to the current flowing through the resistor. With the known value of the resistance R, the voltage drop sensed on the resistor indicates the intensity of the current flowing through it.

Assuming an ideal current sense resistor that doesn't change its resistance value when there is a change in the magnitude of the current or a change in environmental conditions, like the ambient temperature or self heating, the measured voltage drop will yield a precise value of the current: I = V/R. But with a real-life resistor, such as a metal film resistor, a change in current intensity (and in the dissipated power) will cause a change in the resistor's value, which will involve a thermal transient period taking a few seconds or longer to stabilize. Therefore, the key to a fast and precise measurement of current is the use of a real-life current sensing resistor like the VCS101, VCS103, or VCS401, which approach, as closely as possible, an ideal resistor. That is, a resistor that is not influenced by changes in the magnitude of the current flowing through it, or by changes in ambient temperature or any other environmental condition.

Samples and production quantities of the new current sensing resistors are available now, with lead times of five days for samples, and eight weeks for standard orders.