N-Channel Depletion Mode MOSFET: Comprehensive Operation Analysis

Explore the unique characteristics and applications of N-Channel depletion mode MOSFETs with Olukey, your authorized distributor of Winsok’s advanced semiconductor solutions. Understand how these specialized components can enhance your circuit designs with their normally-on characteristics and distinctive operational features.

Understanding Depletion Mode MOSFET Fundamentals

Unlike enhancement mode MOSFETs, depletion mode devices are normally-on at zero gate-source voltage, offering unique advantages in specific circuit applications. This fundamental characteristic stems from their physical structure and fabrication process.

Key Characteristics

Normally-on operation (conducts at V_GS = 0V)
Requires negative gate voltage for turn-off
Built-in channel during fabrication
Higher current handling capability at zero gate bias
Unique transfer characteristics curve

Operating Regions and Characteristics

Cut-off Region

V_GS < V_P (Pinch-off voltage)

Channel fully depleted
No current flow
Device acts as open circuit

Linear Region

V_GS > V_P and V_DS < V_GS – V_P

Channel partially depleted
Device acts as voltage-controlled resistor
Linear I-V characteristics

Saturation Region

V_GS > V_P and V_DS > V_GS – V_P

Channel pinched off at drain end
Current remains constant
Ideal for amplification

Mathematical Model and Equations

Linear Region Current Equation:

I_D = I_DSS(1 – V_GS/V_P)²[2(V_DS/V_P) - (V_DS/V_P)²]

Saturation Region Current Equation:

I_D = I_DSS(1 – V_GS/V_P)²

Where:

I_DSS = Saturated drain current at V_GS = 0V
V_P = Pinch-off voltage (negative for n-channel)
V_GS = Gate-to-source voltage
V_DS = Drain-to-source voltage

Winsok’s N-Channel Depletion MOSFET Portfolio

Model	I_DSS (mA)	V_P (V)	R_DS(on) (Ω)	Applications
WS-DN100	10-15	-2.5	50	Low-power amplifiers
WS-DN200	20-30	-3.0	35	Current sources
WS-DN300	50-75	-4.0	20	Power supplies
WS-DN400	100-150	-5.0	10	High-power applications

Selecting the Right Depletion Mode MOSFET

Choosing the appropriate depletion mode MOSFET requires careful consideration of multiple parameters and application requirements. Here’s a comprehensive selection guide to help you make informed decisions.

Primary Selection Parameters

Parameter	Description	Selection Considerations
I_DSS	Zero-gate drain current	Should be 20-30% higher than required operating current Consider temperature derating Account for batch variations
V_P (Pinch-off Voltage)	Gate voltage required to turn off the device	Must be compatible with available negative supply Consider noise margins Temperature coefficient effects
R_DS(on)	On-state resistance	Critical for power loss calculations Temperature dependence Impact on voltage drop
C_iss, C_oss, C_rss	Input, output, and reverse transfer capacitances	Crucial for high-frequency applications Switching speed requirements Driver circuit compatibility

Application-Specific Selection Guide

Constant Current Source Applications

Key Parameters:
- I_DSS tolerance
- Temperature coefficient
- Output impedance
Recommended Model: WS-DN200 Series
- ±5% I_DSS tolerance
- Optimized temperature characteristics

High-Frequency Applications

Key Parameters:
- Input/output capacitances
- Switching characteristics
- Gate charge
Recommended Model: WS-DN300 Series
- Low gate charge
- Optimized for RF applications

Power Applications

Key Parameters:
- Power dissipation
- Safe operating area
- Thermal resistance
Recommended Model: WS-DN400 Series
- Enhanced thermal performance
- Robust SOA characteristics

Selection Process Workflow

Define Application Requirements
- Operating current range
- Voltage requirements
- Frequency of operation
- Temperature range
Calculate Safety Margins
- Current derating (30% recommended)
- Voltage derating (50% recommended)
- Temperature derating
Consider Secondary Parameters
- Package requirements
- Thermal considerations
- Cost constraints
Verify Device Availability
- Production status
- Lead time
- Alternative sources

Key Selection Calculations

Maximum Operating Current: I_{op_max} = I_DSS × 0.7

Power Dissipation: P_D = I_D² × R_DS(on) + V_GS × I_G

Temperature Rise: ΔT = P_D × R_θJA

Need Help Selecting the Right Depletion Mode MOSFET?

Our technical team at Olukey can assist you in choosing the optimal Winsok depletion mode MOSFET for your specific application. We provide:

Detailed technical consultation
Sample evaluation support
Application-specific recommendations
Performance optimization guidance

Get Selection Support

Common Selection Pitfalls to Avoid

Overlooking temperature effects on I_DSS
Insufficient voltage margins for V_GS
Inadequate consideration of switching requirements
Neglecting package thermal limitations
Ignoring long-term reliability factors

Application Circuits and Design Considerations

Constant Current Source

One of the most common applications of depletion-mode MOSFETs is as a constant current source:

Self-biasing capability
High output impedance
Temperature stability considerations
Circuit stabilization techniques

Cascode Amplifiers

Advantages in cascode configurations:

Improved frequency response
Reduced Miller effect
Higher output impedance
Better isolation

Level Shifters

Benefits in level shifting applications:

Wide voltage range handling
Low power consumption
High-speed operation
Simple implementation

Protection Circuits

Usage in protection schemes:

Overcurrent protection
Voltage clamping
Fail-safe operation
Quick response time

Practical Design Considerations

Temperature Effects

Critical parameters affected by temperature:

Threshold voltage drift
Channel mobility variations
Leakage current changes
Performance degradation considerations

Parameter	Temperature Coefficient	Compensation Method
Threshold Voltage	-2mV/°C	Temperature sensing feedback
Mobility	-0.7%/°C	Current mirror compensation
On-Resistance	0.7%/°C	Active biasing network

Advanced Applications

RF Circuit Applications

Mixer circuits
RF amplifiers
Impedance matching networks
Frequency multipliers

Analog Signal Processing

Variable gain amplifiers
Active filters
Sample and hold circuits
Analog multiplexers

Power Management

DC-DC converters
Linear regulators
Battery charging circuits
Power distribution

Reliability and Lifetime Considerations

Critical Reliability Factors

Gate oxide integrity
Hot carrier effects
Thermal cycling endurance
ESD protection requirements
Operating environment considerations

Expert Support for Your Depletion Mode MOSFET Applications

Partner with Olukey for access to Winsok’s premium N-channel depletion mode MOSFETs and comprehensive technical support. Our engineering team is ready to assist with your specific application requirements.

Get Design Support
Request Samples