JFET Pin Identification Guide for Circuit Designers

1. Visual Inspection by Package Type

Most JFETs follow specific pin configurations based on their package:

• TO-92 (Plastic Package): Hold the device with the flat side facing you. The pins typically align as Drain (D), Gate (G), Source (S) from left to right . However, variations exist (e.g., some manufacturers use G-D-S).

• TO-220 (Metal Package): The tab is connected to the Drain (D), with Gate (G) and Source (S) adjacent .

• Four-Pin JFETs: An extra pin serves as a shielding electrode (grounded during operation) .

2. Multimeter-Based Identification

Use a digital multimeter (DMM) in Diode Test Mode or R×1kΩ resistance mode:

• Identify the Gate (G):

• Touch the DMM’s black probe to one pin and the red probe to the other two.

• If both readings are high (reverse bias), the black probe is on the Gate (G) for an N-channel JFET.

• If both readings are low (forward bias), it’s a P-channel JFET .

• Distinguish Source (S) and Drain (D):

• For N-channel JFETs: Connect the black probe to G and the red probe to S (forward bias). Reverse the probes for D (reverse bias) .

• For P-channel JFETs: Swap the probe polarities.

3. Symmetry Check

JFETs are symmetrical in most cases, meaning S and D can be interchanged without affecting functionality . Verify this by measuring the resistance between S and D—it should be low and consistent in both directions .

4. Advanced Testing (Optional)

For critical applications, assess the JFET’s transconductance (gm) using the R×100Ω mode:

• Connect the red probe to S and the black probe to D.

• Touch the G with a finger to induce a small voltage. A noticeable needle swing indicates proper amplification .

Key Notes

• Safety: Always power off the circuit before testing.

• ESD Protection: While JFETs are less sensitive than MOSFETs, avoid static discharge during handling.

• Documentation: Refer to the datasheet for exact pinouts, as variations exist across manufacturers.

As a trusted semiconductor provider, YFW Microelectronics ensures precision-engineered JFETs with consistent pin configurations for reliable performance. For tailored solutions, explore our product lineup or contact our technical support.