4.7 Ohm Resistor: Color Code & Applications – Power Electronics Guide

Three years into my career, I destroyed a $12,000 motor controller prototype because I grabbed a 4.7k resistor instead of a 4.7 ohm resistor for a current-sensing circuit. Both had yellow-violet color bands. The difference? One tiny gold band versus a red band as the multiplier. That expensive lesson taught me to triple-check low-value resistors – they’re deceptively easy to confuse, and the consequences in power circuits are catastrophic.

Working in power electronics and motor control for the past twelve years, I’ve learned that 4.7 ohm resistors occupy a unique niche. They’re too high for heavy current sensing (where you’d use milliohm values) but perfect for moderate-current applications, LED current limiting, speaker protection, and dozens of other circuits where you need a few ohms of resistance. Let me share the practical knowledge that keeps these components working reliably in real-world designs.

What Is a 4.7 Ohm Resistor?

A 4.7 ohm resistor provides precisely 4.7Ω of resistance – a relatively low value in the resistor world. Unlike the kilohm resistors (4.7kΩ = 4,700Ω) commonly used in signal circuits, the 4.7 ohm resistor handles significantly more current with much less voltage drop.

The practical implications: at 1 amp, a 4.7Ω resistor drops only 4.7V and dissipates 4.7W of power. Compare that to a 470Ω resistor which would drop 470V at 1A (completely impractical). This makes the 4.7 ohm resistor ideal for power-level applications where you need some resistance but can’t afford huge voltage drops or power losses.

In the E12 series of standard values, 4.7 appears frequently: 0.47Ω, 4.7Ω, 47Ω, 470Ω, 4.7kΩ, 47kΩ, 470kΩ. The pattern repeats across decades, which is why color code reading is absolutely critical.

Decoding the 4.7 Ohm Resistor Color Code

Here’s where things get tricky. The 4.7 ohm resistor looks dangerously similar to other values, and misidentification leads to immediate circuit failure in power applications.

Standard 4-Band Color Code

The most common 4.7 ohm resistor uses these color bands:

Band Position	Color	Meaning	Value
1st Band	Yellow	First Digit	4
2nd Band	Violet	Second Digit	7
3rd Band	Gold	Multiplier	× 0.1
4th Band	Gold/Silver	Tolerance	±5% / ±10%

Calculation: 47 × 0.1 = 4.7Ω

The critical detail is the gold third band. Gold as a multiplier means “divide by 10” or “multiply by 0.1.” This single band distinguishes 4.7Ω from:

• 47Ω (Yellow-Violet-Black-Gold): Black multiplier = ×1
• 470Ω (Yellow-Violet-Brown-Gold): Brown multiplier = ×10
• 4.7kΩ (Yellow-Violet-Red-Gold): Red multiplier = ×100

With ±5% tolerance, your actual measured resistance falls between 4.465Ω and 4.935Ω. For most power applications, this tolerance is acceptable.

5-Band Precision Color Code

Higher-precision 4.7 ohm resistors use five color bands:

Band Position	Color	Meaning	Value
1st Band	Yellow	First Digit	4
2nd Band	Violet	Second Digit	7
3rd Band	Black	Third Digit	0
4th Band	Silver	Multiplier	× 0.01
5th Band	Brown/Gold	Tolerance	±1% / ±5%

Calculation: 470 × 0.01 = 4.70Ω

The 1% tolerance (brown band) gives you a range of 4.653Ω to 4.747Ω – important when you need precise current sensing or when matching resistors for parallel configurations.

Color Code Comparison: Avoiding Confusion

This table shows how easily you can grab the wrong resistor:

Resistance	4-Band Code	Key Identifier
0.47Ω	Yellow-Violet-Silver-Gold	Silver multiplier (÷100)
4.7Ω	Yellow-Violet-Gold-Gold	Gold multiplier (÷10)
47Ω	Yellow-Violet-Black-Gold	Black multiplier (×1)
470Ω	Yellow-Violet-Brown-Gold	Brown multiplier (×10)
4.7kΩ	Yellow-Violet-Red-Gold	Red multiplier (×100)

Critical safety note: Always verify low-value resistors with a multimeter before installation in power circuits. The cost of a meter reading is trivial compared to replacing damaged components.

Practical Applications for the 4.7 Ohm Resistor

After designing dozens of power supply and motor control boards, these are the applications where 4.7 ohm resistors consistently prove their worth.

Current Sensing in Power Circuits

This is probably the most common application I see. A 4.7 ohm resistor placed in series with a load allows you to measure current by monitoring voltage drop.

Example: 2A motor current sensing

At 2 amps, the voltage drop across a 4.7Ω resistor is:

• V = I × R = 2A × 4.7Ω = 9.4V
• Power dissipation: P = I²R = 4A² × 4.7Ω = 18.8W

This is actually too high for most circuits. Let me show you a more practical example.

Better example: 500mA current sensing

Parameter	Value	Notes
Current	0.5A	Typical for small DC motors
Voltage drop	2.35V	Acceptable in 12V circuits
Power dissipation	1.175W	Use 2W or 3W resistor
Measurement resolution	2.35mV/mA	Easy to amplify

The 2.35V drop is measurable with basic op-amps or even microcontroller ADCs. You’d typically use an instrumentation amplifier to measure the voltage, then calculate current via Ohm’s law.

Why not use lower values? For small currents (<1A), lower resistor values like 0.47Ω or 0.1Ω produce voltage drops that are difficult to measure accurately without specialized amplifiers. The 4.7Ω value provides good signal-to-noise ratio for moderate currents.

LED Current Limiting

In higher-voltage circuits, 4.7 ohm resistors work perfectly for limiting LED current. Let me show you when this makes sense.

24V automotive/industrial application:

Component	Specification
Supply voltage	24V
LED forward voltage	3.2V (white LED)
Desired LED current	20mA
Required resistance	(24V – 3.2V) / 0.02A = 1,040Ω

Wait – this example shows you wouldn’t use 4.7Ω here. Let me show you where it works:

Correct application – Low voltage with power LED:

Component	Specification
Supply voltage	5V
Power LED forward voltage	3.5V
LED forward current	300mA
Required resistance	(5V – 3.5V) / 0.3A = 5Ω
Nearest standard value	4.7Ω
Actual LED current	320mA (close enough)
Power dissipation	0.48W (use 1W resistor)

Power LEDs in 5V circuits are where 4.7Ω shines. The low resistance doesn’t waste much power while still providing adequate current limiting.

Speaker Protection Circuits

Audio engineers use 4.7 ohm resistors in speaker crossover networks and protection circuits. Here’s why:

Most loudspeakers have impedances of 4Ω or 8Ω. A 4.7Ω series resistor:

• Provides tweeter protection in crossover networks
• Limits current during transients
• Helps impedance matching
• Dissipates minimal power during normal operation

Example calculation:

• 8Ω speaker driven at 10W
• Current: I = √(P/R) = √(10W/8Ω) = 1.12A
• Voltage drop across 4.7Ω: 1.12A × 4.7Ω = 5.26V
• Power loss in resistor: 5.9W

For high-power audio, you’d use a 10W or higher rated resistor to handle peaks safely.

Inrush Current Limiting

When powering capacitive loads or switching power supplies, inrush current can damage switches and connectors. A 4.7 ohm resistor temporarily limits this surge.

Typical implementation:

• 4.7Ω resistor in series with load
• Relay or MOSFET to bypass resistor after startup
• Limits initial surge to safe levels

I’ve used this technique in battery-powered equipment where the initial capacitor charging would otherwise trip the protection circuits.

Pull-Down Resistors for High-Current Gates

In power MOSFET gate drive circuits, 4.7 ohm resistors sometimes serve as pull-down resistors. Unlike the 10kΩ pull-downs used in logic circuits, these low values:

• Rapidly discharge gate capacitance
• Ensure fast turn-off times
• Prevent parasitic turn-on during switching

This application requires careful thermal design since the resistor handles gate charge/discharge current.

Power Rating Selection – Critical for Low-Value Resistors

Power rating matters enormously with low-value resistors. Miss this calculation, and you’ll have burned components.

Power Dissipation Calculation

For any resistor: P = I²R or P = V²/R

Let’s work through real examples:

Current	Resistance	Power Formula	Power Dissipated	Minimum Rating
100mA	4.7Ω	I²R	0.047W	1/8W (0.125W)
500mA	4.7Ω	I²R	1.175W	2W
1A	4.7Ω	I²R	4.7W	5W or 10W
2A	4.7Ω	I²R	18.8W	20W or 25W

Design rule: Always use a resistor rated for at least 2x your calculated power dissipation. For current-limiting applications where the resistor might see brief overcurrent, use 3-5x margin.

Common Power Ratings for 4.7Ω Resistors

Power Rating	Package Type	Typical Current	Use Case
1/4W	Small through-hole	<250mA	Signal level, low-power LED
1W	Standard through-hole	<450mA	Moderate current limiting
2W	Larger axial/wirewound	<650mA	Current sensing, LED arrays
5W	Wirewound/ceramic	<1A	Power supplies, motor circuits
10W+	Large wirewound/aluminum	>1A	High-power applications

SMD packages are generally limited to 1W maximum for 4.7Ω values. For higher power, you need through-hole wirewound or metal element resistors with proper heatsinking.

Resistor Types and When to Use Each

Carbon Film Resistors

Pros:

• Inexpensive ($0.02-0.05 in volume)
• Adequate for non-critical applications
• Easy to source

Cons:

• High temperature coefficient (200-500 ppm/°C)
• Tolerance typically ±5%
• Not ideal for precision current sensing

Use for: General-purpose current limiting, non-critical applications, prototyping

Metal Film Resistors

Pros:

• Better tolerance (±1% common)
• Lower temperature coefficient (50-100 ppm/°C)
• More stable over time
• Negligible additional cost

Cons:

• Slightly more expensive than carbon film
• Power ratings limited in small packages

Use for: Current sensing where accuracy matters, voltage dividers, any precision application

Wirewound Power Resistors

Pros:

• High power ratings (5W to 100W+)
• Excellent thermal stability
• Very low tolerance available
• Can handle surge currents

Cons:

• Inductive (problematic in high-frequency circuits)
• More expensive
• Larger physical size

Use for: High-current applications, power supplies, motor control, anywhere >2W dissipation expected

Metal Element / Current Sense Resistors

Pros:

• Very low inductance
• Excellent stability
• High power density
• Four-terminal (Kelvin) connection available
• Low temperature coefficient

Cons:

• Expensive ($1-5 per piece)
• Limited value selection
• Requires proper PCB layout

Use for: Precision current sensing, battery management systems, motor controllers, power measurement

Critical Design Considerations

Temperature Effects

Low-value resistors dissipate significant power, generating heat. This affects:

Resistance drift: A carbon film 4.7Ω resistor at 300 ppm/°C:

• Temperature rise: 50°C above ambient
• Resistance change: 4.7Ω × 300ppm × 50°C = 0.071Ω
• Percentage change: 1.5%

For current sensing, this 1.5% error might be acceptable. For precision applications, use metal film or current-sense resistors.

Self-heating: Calculate resistor temperature rise:

• Power dissipation: 2W
• Thermal resistance: ~60°C/W (typical for 2W resistor)
• Temperature rise: 2W × 60°C/W = 120°C

This brings a 25°C ambient to 145°C – within the 155°C rating of most resistors, but marginal. Always check thermal derating curves in the datasheet.

PCB Layout for Low-Value Resistors

Trace resistance matters: At 4.7Ω, even PCB traces add significant resistance.

1oz copper, 10mm × 1mm trace = ~0.17Ω. That’s 3.6% of your resistor value!

Best practices:

• Use wide, short traces (minimize trace resistance)
• For current sensing, use four-terminal (Kelvin) connections
• Provide adequate copper for heat dissipation
• Consider copper pour under high-power resistors
• Use thermal vias if needed

Parallel and Series Configurations

Parallel resistors for higher power:

Two 4.7Ω, 2W resistors in parallel:

• Total resistance: 2.35Ω
• Total power rating: 4W

This technique doubles your power capacity but halves resistance.

Series resistors for higher voltage:

Need 4.7Ω at 10W but only have 5W parts?

• Use two 2.35Ω, 5W resistors in series
• Total resistance: 4.7Ω (close enough to 4.7Ω)
• Total power rating: 10W

Testing and Verification

Using a Multimeter

To measure a 4.7 ohm resistor:

1. Set meter to lowest resistance range (usually 200Ω)
2. Important: Zero your meter first (touch probes together, note reading)
3. Measure the resistor
4. Subtract the zero reading

Example:

• Probes shorted: 0.3Ω
• Resistor measured: 5.1Ω
• Actual resistance: 5.1Ω – 0.3Ω = 4.8Ω (within ±5% tolerance)

Cheap multimeters often have 0.2-0.5Ω of lead resistance. Better meters have dedicated low-resistance modes with four-terminal measurement.

In-Circuit Testing

Testing 4.7Ω resistors while installed is nearly impossible unless you:

• Desolder one end (most reliable method)
• Use a four-wire meter with Kelvin clips
• Account for parallel paths in your measurement

For current-sensing applications, I verify by measuring the voltage drop at a known current and calculating the resistance.

Helpful Resources and Tools

Online Calculators

Resistor color code tools:

• Digi-Key Resistor Color Code Calculator: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code
• All About Circuits Calculator: https://www.allaboutcircuits.com/tools/resistor-color-code-calculator/
• Electronics-Tutorials Color Code Guide: https://www.electronics-tutorials.ws/resistor/res_2.html

Power dissipation calculators:

• LED Resistor Calculator: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-led-series-resistor
• Ohm’s Law Calculator: https://www.rapidtables.com/calc/electric/ohms-law-calculator.html

Component Distributors

For purchasing 4.7 ohm resistors:

• Mouser Electronics (https://www.mouser.com) – Excellent filters for power rating and tolerance
• Digi-Key (https://www.digikey.com) – Best parametric search
• Newark/Farnell (https://www.newark.com) – Good for industrial quantities
• LCSC (https://www.lcsc.com) – Best pricing for Asian manufacturing

Manufacturer Resources

Recommended manufacturers for power resistors:

• Vishay – Industry standard, excellent datasheets
• Ohmite – Specialists in power and current-sense resistors
• KOA Speer – Great wirewound selection
• Yageo – Cost-effective general-purpose resistors
• Bourns – Precision current-sense resistors

Application Notes

• Vishay “Current Sense Resistors” Application Note
• TI “Current Sensing Techniques” SLYT085
• Linear Technology AN105 “Accurate Current Sensing”

These application notes are invaluable for understanding the nuances of using low-value resistors in real circuits.

Frequently Asked Questions

What’s the difference between a 4.7 ohm resistor and a 4.7k ohm resistor?

The difference is massive: 4.7Ω = 4.7 ohms, while 4.7kΩ = 4,700 ohms – that’s a 1000x difference. They look similar (both have yellow-violet bands) but serve completely different purposes. The 4.7Ω resistor handles higher currents with minimal voltage drop (power applications), while 4.7kΩ is used in signal circuits. The color code multiplier band is key: gold (÷10) for 4.7Ω versus red (×100) for 4.7kΩ.

Can I use a 4.7 ohm resistor for current sensing with a microcontroller?

Yes, but you need to calculate if the voltage drop is adequate for your ADC. At 500mA, a 4.7Ω resistor drops 2.35V – easily readable by most microcontroller ADCs. However, at lower currents (100mA = 0.47V), you might need an op-amp to amplify the signal. Also consider power dissipation – a 500mA current requires a 2W rated resistor minimum. For precision applications, use a 1% metal film resistor and account for its temperature coefficient.

How do I choose between carbon film, metal film, and wirewound 4.7 ohm resistors?

Choose based on power requirements and precision needs: (1) Carbon film: cheap, adequate for non-critical applications <1W. (2) Metal film: better tolerance and temperature stability, use for current sensing up to ~2W. (3) Wirewound: high power (>2W), excellent for motor control and power supplies. Note that wirewound resistors are inductive – avoid them in high-frequency circuits. For precision current sensing at any power level, use dedicated current-sense resistors with four-terminal connections.

What power rating do I need for a 4.7 ohm resistor in my circuit?

Calculate using P = I²R where I is your maximum current. Then multiply by 2-3 for safety margin. Examples: at 100mA you need >0.1W (use 1/4W), at 500mA you need >2.4W (use 5W), at 1A you need >9.4W (use 10W or 20W). Don’t forget to check if your circuit has surge currents or fault conditions that could temporarily increase current. High-power resistors also need proper PCB layout with wide traces and thermal management.

Why does my 4.7 ohm resistor get hot, and is this normal?

Yes, heating is normal and expected for low-value resistors carrying significant current. Power dissipation follows P = I²R, so even moderate currents generate substantial heat. At 500mA, a 4.7Ω resistor dissipates 1.175W – that’s enough to make it uncomfortably hot to touch. As long as you’ve selected the correct power rating (with safety margin) and the resistor stays below its maximum operating temperature (~155°C typically), this is fine. If it’s getting too hot, either reduce current, use a higher power rating, or use multiple resistors in parallel to distribute the heat.

Final Thoughts from the Field

The 4.7 ohm resistor occupies an interesting middle ground – too low for signal work, too high for heavy current sensing, but perfect for a surprisingly large range of power electronics applications. After debugging countless circuits where someone used the wrong low-value resistor, I’ve learned that discipline in component selection and verification is absolutely critical.

My practical advice: maintain separate storage for low-value resistors (<10Ω), label them clearly with both color code and printed value, and always – always – verify with a meter before soldering into power circuits. A $0.05 resistor error can easily cause $500 in damaged components.

Stock both carbon film (for general use) and metal film (for current sensing) versions in common power ratings (1/4W, 1W, 2W, 5W). For production designs, specify the exact part number rather than just “4.7Ω resistor” – it forces you and your assembly house to think about power rating, tolerance, and type.

The 4.7 ohm resistor may not be glamorous, but used correctly, it’s a workhorse component that solves real problems in power electronics, motor control, LED driving, and audio circuits. Just don’t confuse it with 4.7kΩ – that’s a mistake you only make once.