# How TVS diode suppress voltage

#### mohan.n221993

Joined Dec 11, 2019
3
Hi all when i'm going through many datasheets got to know that TVS can suppress transients .

My doubt is where the remaining voltage will go?

for example we use TVS with clamp voltage of 20V and if we give 30 voltage as input it will provide voltage to load by clamping input to 20V .

My doubt is 30-20=10V what happens to this remaining 10V ?

#### dl324

Joined Mar 30, 2015
16,914
Welcome to AAC!

A TVS diode is like a zener diode that can dissipate hundreds of watts. A fuse is often put in series with the diode to avoid damage to the diode.

#### mohan.n221993

Joined Dec 11, 2019
3
Hi Sir,

Can you please elaborate the answer because i'm new to Hardware designing.

What i know is

Zener will clamp voltage once voltage across it exceeds its clamp rating by reducing its impedance by allowing more current flowing through it.

I'm not able to understand what is relation between input extra voltage(inputv/g-zener v/g=extra voltage) and current or power dissipation through diode .

#### dl324

Joined Mar 30, 2015
16,914
Zener will clamp voltage once voltage across it exceeds its clamp rating by reducing its impedance by allowing more current flowing through it.

I'm not able to understand what is relation between input extra voltage(inputv/g-zener v/g=extra voltage) and current or power dissipation through diode .
Zener diodes "clamp" the input voltage to their nominal voltage, but they aren't high power devices (typically 5W or less) and a series resistor is used to limit the maximum current and, therefore, power dissipation.

TVS diodes are like high power zener diodes (hundreds of watts), but a fuse is often used to prevent the TVS diode from being destroyed.

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#### tindel

Joined Sep 16, 2012
936
A fuse is often put in series with the diode to avoid damage to the diode.
Then what what sort of protection is the TVS really providing?

I don’t use TVS’s. Not pn junction based ones anyway. At best they are really respec’d zeners with limited protection - if any at all. At worst they hide fundamental flaws in the design.

Props to the marketing folks for designing this additional revenue stream!

#### dl324

Joined Mar 30, 2015
16,914
Then what what sort of protection is the TVS really providing?
Transient voltage suppression.

The fuse is to protect the TVS diode from failing (which is usually a short) because a fuse is usually easier to replace.

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#### tindel

Joined Sep 16, 2012
936
My question was rhetorical to provide thought.