Colorado Electronic Product Design - Analog / Digital Design, Telecommunications, DSP, Embedded Systems

Resistor finder

Finds the nearest resistor to a desired value from the standard "E" families. Resistors are commonly available from 10Ω to 1MΩ, values above and below this range are harder to find. Resistors are readily available as metal film chip resistors in surface mount packages (402, 603, 805, 1206) and leaded axial packages. These parts have fractional power capability. Resistors with larger power capability are less readily available. Ceramic capacitors in 5% and 10% tolerance follow the E24 and E12 rules. They are commonly available from 10pF to 1u. It can be prudent to stick to the E12 values: 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2 when selecting capacitors.

Family
Desired
Low Choice Error
High Choice Error

Resistor divider

Select the variable you wish to find, fill in the other values, and click "Calculate".

Vin
Vout
R1
R2

Resistors in parallel

Select the variable you wish to find, fill in the other values, and click "Calculate".

R1 || R2
R1
R2

RC Time Constant

This applet finds the time constant and corner frequency for a simple RC circuit.

R
C
Time Constant
Corner

SMD Size Vs. Power Dissipation Chart

This is a guideline chart for picking the right size SMD resistor for power dissipation.

Size

Size Metric

Length (in)

Width (in)

Length (mm)

Width (mm)

Height (mm)

Watts

Max Operating Voltage (V)

No Margin Resistance for 3.3V Power Dissipation (Ohms)

0201 0603 0.02 0.01 0.60 0.30 0.25 0.05 25 218
0402 1005 0.04 0.02 1.00 0.50 0.35 0.06 50 182
0603 1608 0.06 0.03 1.55 0.80 0.50 0.1 75 109
0805 2012 0.08 0.05 2.00 1.25 0.50 0.125 150 87
1206 3216 0.12 0.06 3.20 1.60 0.60 0.25 200 44
1210 3225 0.12 0.10 3.20 2.60 0.50 0.5 200 22
1218 3246 0.12 0.18 3.10 4.60 0.90 1.0 200 11
2010 5025 0.20 0.10 5.00 2.60 0.70 0.75 200 15
2512 6432 0.25 0.12 6.30 3.20 0.60 1.0 250 11

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