A Primer on Transient Voltages. Threats originating from lightning, inductive load switching and electrostatic discharge are reviewed and defined along with their damaging effects on microchips.
An Introduction to Transient Voltage Suppressor Devices. Describes and illustrates the performance of the basic types of transient voltage suppressors (TVSs) including gas discharge tubes, metal oxide varistors (MOVs), silicon pn junction TVSs and thyristors.
What is a Silicon Transient Voltage Suppressor? Illustrates why a silicon TVS is needed, how it diverts transient current away from vulnerable circuitry and reviews device pulse power ratings.
Using the Power vs Time Curve. Guides the reader in determining peak pulse power and peak pulse current for pulse widths of different values than those specified for a given device.
What is a Thyristor Surge Protector Device? Reviews the basics of an avalanche voltage triggered thyristor designed for transient voltage protection, used largely for telecom signal lines.
Crowbars and Clamps. Reviews the major differences including the low on-state voltage of the crowbar and the ease of transition from conduction to non-conduction for the clamp. Trade-offs and applications are discussed.
Cross Referencing TVS Devices. Accentuates the electrical parameters to be compared when replacing an axial leaded device with an equivalent surface mount component. Illustrations are given in making selections.
Determining a Range of Clamping voltages for a Range of Pulse Currents. Provides a formula for calculating the clamping voltage for values of surge current at lower values than the peak rating. Sample calculation depicts simplicity of concept.
Protecting From Electrostatic Discharge. Emphasizes the fast, subnanosecond rise-time of static discharge and the need for low parasitic inductance in protective devices and requirements for shielding where applicable.
Parasitic Capacitance In Transient Voltage Supressors. Illustrates the inherent capacitance values in a silicon TVS and how to minimize this effect with low capacitance silicon diode elements where required.
MicroNote 111
Parasitic Lead Inductance on Transient Voltage Suppressors. Reduced protection offered by a TVS results when longer than tolerable component lead lengths product overshoot voltages resulting from L(di/dt) effects.
MicroNote 112
Series Stacking of Silicon TVSs For Higher Surge Current. Series stacking of TVSs can be employed to increase peak pulse power and surge current since power is additive for parts in series. Practical applications are illustrated.
MicroNote 113
Parallel Stacking of Silicon TVSs For Higher Surge Current. For lower voltage applications, higher surge capability can be achieved by parallel stacking. Devices must be matched very closely for load sharing, within 50 mV for an 8V requirement and within 200 mV for 30V. Examples are shown.
MicroNote 114
Derating of Silicon TVSs For Higher Junction Temperatures. Most silicon TVSs are derated linearly from max rating at 25°C down to zero at 175°C. this note shows the reader how to use the derating curve for assigning the maximum surge rating for a device at any point between 25°C and 175°C.
MicroNote 115
Derating Transient Voltage Supressors at Elevated Temperatures For Varying Pulse Widths. This note combines the information in MicroNotes 114 and 104 above to accommodate those conditions in which temperature is above 25°C and pulse width varies significantly from specified conditions.
MicroNote 116
Protection at a Transformer Input. Illustrates the chief advantage, which is higher surge rating, of placing the TVS on the low voltage secondary output. A case history is used in depicting this advantage.
Copyright Microsemi Corporation 1996
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