SF31G to SF38G Rectifier Diodes: Features, Uses, and Specifications

The SF31G to SF38G series are fast recovery rectifier diodes designed for high-efficiency switching power supplies, inverters, and general rectification applications. These diodes are well-known for their fast recovery time, high surge capability, and reliable performance, making them ideal for use in various AC to DC conversion circuits.

In this article, we’ll cover the key features, electrical specifications, and typical applications of the SF31G to SF38G diode series to help you select the right one for your power electronic designs.

What are SF31G to SF38G Diodes?

The SF3xG series are glass-passivated junction fast recovery rectifiers, where:

"SF" stands for "Super Fast" recovery.
The last two digits (31 to 38) denote the voltage rating.

These diodes are housed in DO-27 axial packages and are commonly used in switch-mode power supplies (SMPS), battery chargers, and motor drives where speed and reliability are critical.

✅ Key Features of SF31G–SF38G Series

⚡ High Voltage Ratings from 50V to 800V
Fast Reverse Recovery Time: ~150ns typical
Average Forward Current: 3A
High Surge Current Capability: Up to 100A (8.3ms single half sine-wave)
️ Wide Operating Temperature: –65°C to +150°C
Low Forward Voltage Drop: Reduces power loss
️ Glass Passivated Junction: Improves reliability and thermal stability
DO-27 Axial Lead Package for through-hole mounting

Electrical Specifications (Summary)

Parameter	SF31G	SF32G	SF33G	SF34G	SF35G	SF36G	SF37G	SF38G
Max Repetitive Voltage (Vrrm)	50V	100V	200V	400V	600V	800V	1000V	1200V
Average Forward Current (Io)	3A	3A	3A	3A	3A	3A	3A	3A
Peak Forward Surge Current (Ifsm)	100A	100A	100A	100A	100A	100A	100A	100A
Reverse Recovery Time (trr)	~150ns	~150ns	~150ns	~150ns	~150ns	~150ns	~150ns	~150ns
Max Forward Voltage (Vf) @ 3A	1.3V	1.3V	1.3V	1.3V	1.3V	1.3V	1.3V	1.3V

All members of the series are functionally identical except for the voltage rating, making them interchangeable based on application voltage requirements.

Common Applications

⚙️ Switch Mode Power Supplies (SMPS)
- Used for output rectification or snubber circuits.
Battery Chargers
- Ensures fast and efficient rectification with minimal losses.
Home Appliances
- Provides AC to DC conversion in motors, fans, and controllers.
Automotive Electronics
- Used in DC-DC converters and battery protection circuits.
Computer Power Supplies
- Rectification for high-speed switching supplies.
Industrial Automation
- Power rectification in motor drives and PLCs.

⚙️ Thermal and Mechanical Characteristics

Operating Junction Temperature: –65°C to +150°C
Storage Temperature Range: –65°C to +175°C
Mounting: Axial-lead (DO-27 package)
Polarity: Cathode marked with a band

Advantages of Using SF3xG Series

✅ Excellent high-voltage rectification performance
✅ Reduced switching losses due to fast recovery
✅ High reliability and long operational life
✅ Easy to mount with through-hole design
✅ Compatible with leaded and RoHS-compliant assembly

The SF31G to SF38G series are reliable and versatile fast recovery rectifier diodes suitable for a wide range of AC-to-DC conversion and power rectification applications. Their fast switching, high surge current handling, and wide voltage range make them a popular choice for engineers, hobbyists, and industrial designers alike.

Whether you're building a switching power supply, a motor controller, or a battery charger, choosing the correct member of the SF3xG family ensures efficiency, stability, and longevity in your design.

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