Field effect transistors (Fets):MOSFET Safety Precautions

MOSFET Safety Precautions

Certain safety precautions must be observed when handling and using MOSFETs. It is important to check the manufacturer’s specification sheet for maximum rating of EGS.

C a U T I O N !

If EGS is increased too much, the thin insulating layer ruptures, ruining the device. The insulating layer is so sensitive that it can be damaged by a static charge that has built up on the leads of the device. Electrostatic charges on fingers can be transferred to the MOSFET’s leads when handling or mounting the device.

To avoid damage to the device, MOSFETs are usually shipped with the leads shorted together. Shorting techniques include wrapping leads with a shorting wire, inserting the device into a shorting ring, pressing the device into conductive foam, taping several devices together, shipping in antistatic tubes, and wrapping the device in metal foil.

Newer MOSFETs are protected with zener diodes electrically connected between the gate and source internally. The diodes protect against static discharges

and in-circuit transients and eliminate the need for external shorting devices. In electronics, a transient is a temporary component of current existing in a circuit during adjustment to a load change, voltage source difference, or line impulse.

If the following procedures are followed, unprotected MOSFETs can be handled safely:

1. Prior to installation into a circuit, the leads should be kept shorted together.

2. The hand used to handle the device should be grounded with a metallic wristband.

3. The soldering iron tip should be grounded.

4. A MOSFET should never be inserted or removed from its circuit when the power is on.

QUESTIONS

1. What is the reason that MOSFETs have to be handled very carefully?

2. What voltage source, if exceeded, can ruin a MOSFET?

3. What methods are used to protect MOSFETs during shipping?

4. What precautions have been taken to protect newer MOSFETs?

5. Describe the procedures that must be observed when handling unprotected MOSFETs.

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