RDS(on) in MOSFETs: The Critical Parameter for Power Efficiency

When designing power electronic systems, understanding the drain-source on-resistance (RDS(on)) of MOSFETs is crucial for achieving optimal performance and efficiency. As a leading semiconductor distributor, we’ll explore this essential parameter in detail, helping you make informed decisions for your electronic designs.

The Basic RDS(on) Formula

RDS(on) = VDS / ID (when the MOSFET is fully enhanced)

Where:

VDS = Drain-to-Source Voltage
ID = Drain Current

Factors Affecting RDS(on)

Temperature Dependency

RDS(on) typically increases with temperature, following the relationship:

RDS(on) at Tj = RDS(on) at 25°C × (1 + TC × ΔT)

Gate Voltage Impact

Higher gate voltage generally leads to lower RDS(on), until saturation is reached.

Device Construction

Depends on semiconductor material, chip size, and manufacturing process.

Practical Applications and Considerations

Application	Typical RDS(on) Range	Key Considerations
Power Supplies	1-10mΩ	Efficiency critical, heat management important
Motor Drivers	5-50mΩ	Balance between cost and performance
Battery Management	2-20mΩ	Low power loss required

Featured Winsok MOSFETs from Olukey

As the authorized distributor of Winsok MOSFETs, we offer industry-leading solutions with optimized RDS(on) characteristics:

WSF3085 N-channel MOSFET

Ultra-low RDS(on): 1.35mΩ typical
30V rating
85A continuous current
TO-252-2L package

WSK220N04 N-channel MOSFET

RDS(on): 1.2mΩ at VGS=10V
40V rating
220A continuous current
TO-263-2L package

Request Datasheet and Pricing

Advanced RDS(on) Calculations and Considerations

Total Power Loss Calculation

P(loss) = ID² × RDS(on) × D

Where:

P(loss) = Power dissipated in watts
ID = Drain current in amperes
RDS(on) = On-state resistance in ohms
D = Duty cycle (0 to 1)

Temperature Effects on RDS(on)

Temperature (°C)	Typical RDS(on) Multiplier	Design Considerations
25	1.0x	Reference temperature
50	1.3x	Moderate derating needed
75	1.6x	Significant derating required
100	1.9x	Critical thermal management needed
125	2.2x	Maximum recommended operation

Design Optimization Strategies

Parallel Configuration

When MOSFETs are connected in parallel, the effective RDS(on) is calculated as:

RDS(on)_effective = RDS(on) / n

Where n is the number of parallel devices

Thermal Management

Calculate maximum junction temperature:

Tj = Ta + (P_loss × θja)

Where:

Tj = Junction temperature
Ta = Ambient temperature
θja = Thermal resistance junction to ambient

Custom Solutions from Olukey

As a leading semiconductor supplier, we offer:

Comprehensive technical support and consultation
Custom parameter matching for your specific application
Extensive inventory for immediate delivery
Competitive pricing and volume discounts
Reliability testing and qualification support

Request Free Samples

Industry-Specific Applications

Automotive Electronics

Battery management systems
Motor control units
LED lighting drivers
DC-DC converters

Industrial Equipment

Welding equipment
Solar inverters
UPS systems
Industrial drives

Consumer Electronics

Smartphone chargers
Laptop adapters
Home appliances
Gaming consoles

Key Design Recommendations

Always include a safety margin of at least 30% when calculating maximum current ratings
Consider using parallel MOSFETs for high-current applications
Implement proper thermal management solutions
Account for temperature derating in worst-case scenarios
Verify gate drive voltage is sufficient to achieve specified RDS(on)

Ready to optimize your power electronic designs with industry-leading MOSFETs? Contact Olukey today for expert consultation and product selection support.