What is Circuit Design

Circuit Designers try to make connections.

5. What is Inside a Passive Package?

Inductors, Resistors, Capacitors, etc... aren't quite as difficult to make as integrated circuits.  The materials that make the component are encapsulated and formed into standard-sized packages with two or more metal pads that are later soldered to a printed circuit board.

Component Value Calculations

While electrical engineers would like to have every possible value of every component made available to them, this is simply not practical from a manufacturing and inventory management standpoint.  So manufacturers provide standard component values for each order-of-magnitude (decade) based mostly on the equation

E Series Approximation

where m is the E-Series value (6, 12, 24, 48, 96, 192) and n is a positive integer less than m.

Each order-of-magnitude is logarithmically broken into a set number of values.  For E6 series, those values are 1, 1.5, 2.2, 3.3, 4.7, 6.8E6-resistors would have values of

\sqrt[6]{10^0}=1 \sqrt[6]{10^1}\approx 1.5 \sqrt[6]{10^2}\approx 2.2 \sqrt[6]{10^3}\approx 3.3 \sqrt[6]{10^4}\approx 4.7 \sqrt[6]{10^5}\approx 6.8
1 Ω 1.5 Ω 2.2 Ω 3.3 Ω 4.7 Ω 6.8 Ω
10 Ω 15 Ω 22 Ω 33 Ω 47 Ω 68 Ω
100 Ω 150 Ω 220 Ω 330 Ω 470 Ω 680 Ω
1 kΩ 1.5 kΩ 2.2 kΩ 3.3 kΩ 4.7 kΩ 6.8 kΩ

and the series would repeat for each multiple of 10 up into the MΩ range.

There are E-Series divisions into 6, 12, 24, 48, 96, and 192 pieces.  Each series provide additional values that were not seen in the series beneath it.  And very tight-tolerance resistors are available for high E-series devices.

E Series Numberline Plot

As the number of values in the series increases, the tolerance tends to improve, and the cost of the part tends to increase.

If you create a design that requires a 481 Ω 0.1% resistor, take note that 481 Ω only exists as a value in the E192 series -- which means it's going to be significantly more expensive than a 470 Ω 1% resistor taken from the E24 series.

481 Chip Resistor

This is a screenshot of a 481-Ohm E192 series resistor from Digikey.com on 2/17/2020.  At 1kU prices, the components are still $0.12 per part.

470 Ohm Resistor

This is a screenshot of a 470-Ohm E24 series resistor from Digikey.com on 2/17/2020.  At 1kU prices, these parts are less than $0.01.  As you can see, you can spend less to purchase 100,000 of these resistors than 1000 of the 481 Ω resistor shown above

If you need non-standard values of resistors, create them using a series/parallel combination of standard resistors.  Be certain to keep track of uncertainty of measurement as well as power dissipation factors when doing it.

Hard Way Hughes

"You can, I'm certain, order a 500-unit run of 482.3 Ω, laser-trimmed resistors for your next design from a variety of manufacturers.  Just make sure your resume is up to date before submitting the request through purchasing.  The rarer an item, the more expensive it is going to be.

You should also know that I can count on one finger the number of conversations I've had with other engineers about 'E-series' components -- it's generally only discussed by component engineers.  Just be aware that there's a reason some components cost more than others.  Your projects will tend to be more successful and your career will generally last longer if you actively choose the cheaper components wherever possible.  Save the pricier parts for high-end designs."