There are a few fundamental resistor parameters that folks often don’t consider while choosing a resistor. They choose a resistor value and size and call it a day. Please don’t do that. I am listing a few below.
First, every resistor has a Rated Power, the maximum power it can dissipate continuously at its Rated Ambient Temperature. This is what determines whether a resistor blows up or not.
Similarly, Rated Voltage defines the maximum DC or AC (RMS) voltage the resistor can handle without damage. This is the most common mistake I see in designs, using resistors and putting large voltage across them without checking voltage rating. Another one is the Maximum Overload Voltage, which is the max voltage capable of being applied to resistors for a short period in the overload test(Higher than the rated voltage).
Next, Resistor Tolerance indicates how much the actual resistance can deviate from its nominal value, typically expressed as a percentage at 25°C. Keep in mind that resistance also changes with applied voltage (voltage coefficient of resistance, VCR) and temperature (temperature coefficient of resistance, TCR). For example, a TCR of 100 ppm/°C means a 0.1% change per degree Celsius.
Reliability is another critical factor, defined as the probability a resistor will perform its function over time. This is often measured as the Mean Time Between Failures (MTBF) or a failure rate per 1000 hours. Testing at maximum rated conditions over thousands of hours helps predict how resistors will hold up in real-world applications, remember, reliability improves at lower power levels.
Another is Noise which is the unwanted AC signal generated by a resistor. It can harm low-level signals, charge & high-gain amplifiers, and other noise-sensitive applications.
Knowing these parameters helps you choose the right resistor for the job and design circuits that perform reliably under varying conditions. You will find a few of these mentioned in the datasheets.
PS: I should thank Vishay’s App Note for this one as there was a term that I didn’t even know was a considerable factor. 🙂
#BackToBasics #Electronics #Resistors
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