Double Pulse Test Setup Using Oscilloscope: Complete Practical Guide for Power Electronics Engineers

The Double Pulse Test (DPT) is one of the most important experimental techniques used in power electronics. It allows engineers to evaluate the switching performance of MOSFETs, IGBTs, SiC MOSFETs, and GaN HEMTs under controlled conditions.

Today, Double Pulse Testing is widely used in:

• Electric Vehicle Inverter Development
• GaN Converter Design
• SiC Power Module Testing
• Motor Drive Systems
• DC-DC Converter Optimization
• Switching Loss Characterization
• Gate Driver Development
• PCB Layout Validation

One of the most common questions asked by beginners is:

"How do I actually perform a Double Pulse Test using an oscilloscope?"

This guide explains the complete setup, required equipment, probe selection, measurement techniques, waveform interpretation, and common mistakes in simple language.

---

What is a Double Pulse Test?

A Double Pulse Test is a laboratory method used to measure:

• Turn-On Energy (Eon)
• Turn-Off Energy (Eoff)
• Switching Losses
• Voltage Overshoot
• Current Overshoot
• Reverse Recovery Losses
• Switching Speed
• Parasitic Effects

The test applies two gate pulses to the device under test (DUT).

The first pulse establishes the desired load current. The second pulse is used to observe switching behavior and measure losses.

---

Why is DPT Important?

Datasheet values are measured under manufacturer-specific conditions.

Actual converter performance depends on:

• PCB Layout
• Parasitic Inductance
• Gate Resistance
• Load Current
• Temperature
• Bus Voltage

Double Pulse Testing allows engineers to evaluate devices under realistic operating conditions.

---

Equipment Required for Double Pulse Testing

1. Oscilloscope

A high-bandwidth digital oscilloscope is required.

Recommended specifications:

• Bandwidth ≥ 200 MHz
• Sample Rate ≥ 1 GS/s
• 4 Channels Minimum
• Math Functions
• Waveform Integration Capability

---

2. Differential Voltage Probe

Required for measuring drain-source or collector-emitter voltage.

Typical requirements:

• 100 MHz or higher bandwidth
• High Common Mode Rejection
• Suitable Voltage Rating

---

3. Current Probe

Used to measure switching current.

Options include:

• Rogowski Coil
• Current Transformer
• Hall Effect Probe
• Current Shunt

---

4. Gate Driver

A gate driver generates the double pulse sequence.

The driver must provide:

• Correct Gate Voltage
• Proper Dead Time
• Fast Switching Capability

---

5. DC Power Supply

Provides the test bus voltage.

Examples:

• 48 V
• 100 V
• 400 V
• 800 V

Depending on the application.

---

6. Inductive Load

A power inductor is used because most practical power converters operate with inductive current.

---

Basic Double Pulse Test Circuit

The DPT setup typically contains:

• DC Source
• Device Under Test (DUT)
• Freewheeling Diode
• Load Inductor
• Gate Driver
• Voltage Probe
• Current Probe
• Oscilloscope

---

Understanding the Two Pulses

First Pulse

The first pulse charges the inductor current.

Current increases according to:

i = (V/L) × t

Longer pulse width creates higher test current.

---

Dead Time

After the first pulse ends:

• The DUT turns OFF.
• Current transfers to the freewheeling path.
• Current remains nearly constant.

---

Second Pulse

The second pulse is used for:

• Turn-On Energy Measurement
• Reverse Recovery Analysis
• Current Overshoot Observation
• Voltage Overshoot Observation

---

Oscilloscope Channel Configuration

Channel	Signal
CH1	Gate Voltage (VGS)
CH2	Drain-Source Voltage (VDS)
CH3	Drain Current (ID)
CH4	Optional Trigger Signal

---

Where to Connect the Voltage Probe

For MOSFET testing:

• Positive Probe → Drain
• Negative Probe → Source

This measures:

VDS

Always use a differential probe for high-voltage measurements.

---

Where to Connect the Current Probe

The current probe is typically placed around:

• Drain Lead
• Load Inductor Lead
• Busbar Current Path

This measures:

ID

---

Where to Connect the Gate Probe

Gate voltage should be measured directly at the device terminals.

Probe:

• Gate
• Kelvin Source (if available)

This minimizes measurement error.

---

Important Oscilloscope Settings

Bandwidth

Use full oscilloscope bandwidth whenever possible.

Fast GaN transitions may require:

• 200 MHz
• 500 MHz
• 1 GHz

---

Sample Rate

Recommended:

• At least 10× higher than signal frequency content.
• Typically ≥ 1 GS/s.

---

Trigger Configuration

Use gate signal trigger.

This provides stable waveform capture.

---

Measuring Turn-On Energy (Eon)

Instantaneous power is:

P(t) = VDS × ID

Turn-on energy:

Eon = ∫ VDS × ID dt

Modern oscilloscopes can perform:

• Math Multiplication
• Waveform Integration
• Automatic Energy Calculation

---

Measuring Turn-Off Energy (Eoff)

Similarly:

Eoff = ∫ VDS × ID dt

Integration is performed over the turn-off interval.

---

Calculating Switching Loss

Once Eon and Eoff are known:

Psw = fs × (Eon + Eoff)

Where:

• fs = Switching Frequency
• Eon = Turn-On Energy
• Eoff = Turn-Off Energy

---

Observing Voltage Overshoot

Voltage overshoot occurs because of:

• PCB Parasitic Inductance
• Package Inductance
• Busbar Inductance

The relationship is:

V = L × di/dt

High overshoot indicates layout optimization may be required.

---

Observing Current Ringing

Ringing occurs because:

• Parasitic Inductance
• Parasitic Capacitance

Form an unwanted resonant circuit.

Ringing can increase:

• EMI
• Switching Loss
• Device Stress

---

Double Pulse Testing of Silicon MOSFETs

Typical observations:

• Moderate Switching Speed
• Noticeable Reverse Recovery
• Moderate Overshoot

---

Double Pulse Testing of SiC MOSFETs

Typical observations:

• Fast Switching
• Lower Switching Loss
• Higher dv/dt
• Reduced Reverse Recovery

---

Double Pulse Testing of GaN Devices

GaN devices show:

• Extremely Fast Switching
• Very High dv/dt
• Very High di/dt
• Minimal Reverse Recovery

Proper probe placement becomes extremely important.

---

Common Measurement Mistakes

• Using Long Ground Leads
• Incorrect Probe Compensation
• Poor Current Probe Placement
• Insufficient Bandwidth
• Ground Loops
• Incorrect Trigger Setup
• Ignoring Probe Delay Matching

---

Best Practices for Accurate DPT Measurements

• Use Differential Voltage Probes.
• Use High-Bandwidth Current Probes.
• Minimize Probe Loop Area.
• Keep Ground Leads Short.
• Use Kelvin Source Connections.
• Calibrate Probes Properly.
• Verify Timing Alignment.

---

Applications of Double Pulse Testing

• EV Traction Inverters
• Fast Chargers
• Solar Inverters
• GaN Converters
• SiC Power Modules
• Motor Drives
• Data Center Power Supplies
• High-Frequency DC-DC Converters

---

Frequently Asked Questions (FAQs)

Why do we use two pulses instead of one?

The first pulse establishes the desired current level, while the second pulse is used to analyze switching behavior under controlled current conditions.

Can Eon and Eoff be measured directly on an oscilloscope?

Yes. Most modern oscilloscopes provide multiplication and integration functions for energy measurement.

Why is a differential probe recommended?

It safely measures high-side voltages and reduces common-mode measurement errors.

Why is probe placement important?

Incorrect probe placement can introduce measurement noise, ringing, and inaccurate switching energy calculations.

What bandwidth should an oscilloscope have for GaN testing?

Typically 200 MHz minimum, with 500 MHz or higher preferred for very fast switching devices.

---

Key Takeaways

• Double Pulse Testing is the industry-standard method for switching characterization.
• An oscilloscope measures gate voltage, drain voltage, and drain current.
• Eon and Eoff are obtained by integrating VDS × ID.
• Probe selection and placement are critical.
• GaN and SiC devices require high-bandwidth measurement equipment.
• DPT helps optimize efficiency, reliability, and converter performance.

---

Conclusion

A properly configured Double Pulse Test setup provides invaluable information about the dynamic behavior of modern power semiconductor devices. By using a high-bandwidth oscilloscope, suitable probes, proper triggering, and correct measurement techniques, engineers can accurately evaluate switching losses, voltage overshoot, current ringing, and device performance.

Whether developing EV inverters, high-frequency GaN converters, SiC motor drives, or advanced data center power supplies, mastering Double Pulse Testing is an essential skill for every power electronics engineer.