This series won’t be complete without resistor configuration and on how to use them in circuits.
Series: When resistors are placed end-to-end, their values simply add. If you have two resistors R1 & R2 in series, Reff=R1+R2. Req is greater than any single one.
Parallel: When resistors share both connection points(meaning current splits at the point), the reciprocal of the total is the sum of reciprocals: 1/Reff=1/R1+1/R2. This makes Req lower than any single one.
These are the core fundamentals that all of you know by heart from school. Now I want to discuss the cases where it’s useful in complex designs.
Imagine building a precision measurement instrument with op-amps where setting exact gains is crucial. Typically, you’d use highly precise resistors with tight tolerances. However, in practice, variations from the ICs can prevent these resistors from delivering the exact values needed. This is where a combination approach shines. For instance, if you need an effective resistance of 10kΩ for a specific gain, instead of using a single resistor, you can combine multiple resistors to achieve the desired value.
Approach 1: To reach a maximum of 11kΩ, pair a 10kΩ resistor with a 1kΩ resistor and a finely tuned potentiometer. This method works well for increasing resistance. But what if you need to lower it?
Approach 2: Use a three-resistor setup by selecting a larger resistor in one arm and combining a resistor with a potentiometer in the other. This allows you to fine-tune and reduce the overall resistance precisely.
Approach 3: For the flexibility to both increase and decrease resistance, use four resistors, pairing a resistor and potentiometer in each arm. Adjusting each pot lets you finely control the resistance up or down as needed.
These combination techniques are essential for device calibration, allowing folks to compensate for unit variations accurately. Once device calibration is complete, the potentiometers are typically fixed in place with hot glue, ensuring the spec remains stable and reliable.
You can create elegant and precise engineering solutions, by just mastering the simple resistor combinations.
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