TVS diode properties in the forward direction?

[treez]

Hello,
Is the SMAJ200A unidirectional TVS just like a normal diode in forward bias? I realise its Vf is up to 3.5V in forward bias, but does in switch on quickly in the forward direction…like a normal diode?

SMAJ200A TVS datasheet:
https://www.littelfuse.com/products/tvs-diodes/surface-mount/smaj/smaj300ca.aspx

 

[barry]

What's a "normal diode"? What's "fast"? Do you mean fast like a Schottky? Or fast like a 1n4001? When the manufacturer doesn't specify a parameter, it usually suggests that maybe you're trying to use it for something it's not intended for. It says right there on the data sheet:

The SMAJ series is designed specifically to protect sensitive electronic equipment from voltage transients induced by lightning and other transient voltage events.

 

[FvM]

Their Vf isn't higher than other Si diodes. 3.5V is at huge surge current when series resistance dominates. I won't expect fast particular fast rectifier operation of a TVS diode, it has large area and high capacitance.

 

[treez]

Thanks, i believe all diodes like Schottkys, Ultra Fasts, even silicon rects, all turn on super fast....(turn off is different)...but do tvs's turn on fast too?

 

[FvM]

They surely turn on fast, otherwise bipolar TVS diodes won't work.

 

[treez]

Thanks, i am referring to unipolar ones here, in the forward direction.

 

[FvM]

Of course, but a bipolar TVS is a back-to-back series circuit of two unipolar TVS, and one diode is always operated in forward direction. In so far, fast clamping capability of bipolar diodes depends also on the forward characteristic of the basic TVS chip.