How to determine the size of the shunt resistor

In electronic circuit design, shuntingresistance(Shunt Resistor) is a commonly used component for measuring current. It achieves accurate detection of current by producing a tiny voltage drop in the current path. Reasonable selection of the size of the shunt resistor is crucial to ensuring measurement accuracy and circuit performance. This article will introduce in detail the key factors and methods for determining the size of the shunt resistor to help designers make scientific selection.

1. Measuring current range

The first condition for determining the size of the shunt resistor is to clarify the range of the current to be measured. If the resistance value is too large, the voltage drop of the circuit will be too large, affecting normal operation; if the resistance value is too small, the voltage drop will be too low, which is not conducive to signal collection. When designing, it is necessary to calculate the appropriate shunt resistor R_sh based on the maximum current I_max, so that the voltage drop V_sh generated meets the input range of the measuring device:

V_sh = I_max × R_sh

It is generally recommended that the voltage drop be controlled between tens of millivolts and hundreds of millivolts to ensure measurement sensitivity and avoid excessive power consumption.

2. Power consumption considerations

The shunt resistor will produce power loss when working. The calculation formula is:

P = I² × R_sh

Excessive power will cause the resistor to heat up, affecting stability and life. Therefore, when selecting a shunt resistor, ensure that its rated power is greater than 1.5 times the calculated power, and appropriate packaging and heat dissipation measures are used.

3. Measurement accuracy requirements

The accuracy of the shunt resistor directly affects the accuracy of the current measurement. High-precision resistors usually have low temperature coefficients and resistance deviations, and are suitable for occasions that require high measurement accuracy. Common accuracy levels include ±0.1%, ±0.5%, ±1%, etc., which should be selected according to actual needs during design.

4. Effect of temperature coefficient

The resistance of a resistor changes with temperature, and the temperature coefficient (ppm/°C) is a measure of this characteristic. A shunt resistor with a low temperature coefficient can ensure stable measurement results at different operating temperatures, which is especially important in environments with high temperatures or frequent temperature changes.

5. Resistor materials and packaging forms

Commonly used materials for shunt resistors include alloy films, metal foils, etc. Different materials have different resistance stability and temperature characteristics. The packaging form affects the resistor's power handling capability and heat dissipation performance. The selection should take into account board space and heat dissipation requirements.

6. Frequency response requirements

In high-frequency measurement situations, the inductance and capacitance effects of the shunt resistor may affect the measurement accuracy. At this time, a shunt resistor with low inductance should be selected, or a specially designedshuntcomponents to ensure frequency response.

7. Circuit compatibility

The resistance and power of the shunt resistor also need to be compatible with the subsequent signal acquisition circuit. For example, the voltage range and resolution of the ADC input will limit the selection of shunt resistors to ensure that the measured signal is within an acceptable range.

8. Cost and Supply

Under the premise of ensuring performance, reasonable control of the cost and procurement channels of the shunt resistor are also factors that need to be considered during design. Shunt resistors with common specifications are easier to purchase and reasonably priced.

Determining the size of the shunt resistor is a process that comprehensively considers many factors such as measurement current range, power consumption, measurement accuracy, temperature characteristics, material packaging, frequency response and circuit compatibility. Reasonable selection of shunt resistors can not only ensure the accuracy and stability of current measurement, but also improve the performance and reliability of the entire circuit. Designers should scientifically determine the resistance value and specifications of the shunt resistor based on specific application requirements and combined with the above points to ensure the best performance of the measurement system.