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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Operating voltage = voltage at which hardly any current will flow
Breakdown voltage = voltage at which a bit more current will flow
Clamping voltage = voltage when a shit ton of current is flowing.
For the exact values of "hardly any", "bit more" and "shit ton" see the datasheet.
When choosing a TVS, you make the operating voltage a bit more than the actual voltage of the signal you're protecting, and you use the clamping voltage as a guide for the worst-case surge voltage your circuit will see.
Registered Member #3315
Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156
thanks that clears that up.
However can you explain what signal you talking about?
Here is the context i am asking the question in.
I am building a electromagnetic accelerator. It shoots of a 24v lipo battery. My igbt's are rated for 600 volts. I expect around 200 amps of current.pulse length 2ms.
can you give me advice on sizing a bidirectional tvs diode for my application. BTW I am trying to teach myself electronics so i apologize if this is common knowledge.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Depends what circuit topology you're using and what you're expecting the TVS to do. Are you using it as a simple clamp to eat all the inductive energy left in the coil after the projectile has passed through?
Registered Member #3315
Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156
Yes that is exactly what i am trying to do.
Circuit topology is as follows.
My igbt is controlled by 555 timer which is triggered by an ir emitter and detector. The 555 outputs a signal to an inverting igbt driver which then sends the signal to the igbt.
I am under the impression I want the clamping voltage as close to the rating of my igbt (600V) (as an example (x3) 180V TVS in series to get around 540V) In order to burn the leftover energy as quick as possible in order to collapse the magnetic field as quick as possible.
I am still a bit lost on what I would choose as an operating voltage.
I hope this clears things up a bit, thanks for the help man.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
In that case the operating voltage will be 24V, as that's what the TVS sees while the IGBT is on. This is so much lower than 600V, that you can ignore the operating voltage and choose the TVS by clamping voltage only.
The clamping voltage can be a lot higher than the operating voltage, so read the datasheet carefully unless you want to blow stuff up.
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TVS Diode Quick Question
