Tny274 design Replacing VR1 and D5

Posted by: e2f on 06/04/2011

Hi I have a design that calls for:

D5 = FR106 and VR1 = P6KE200A unidirectional

In my design I have replaced VR1 with a SM6T200CA bidirectional TVS instead. I was wondering whether this has a negative effect?

If not, would it then be feasible to remove D5 altogether and just use the bidirectional TVS instead?

Thanks

Comments

What do you mean by bidirectional TVS? Can you draw a sketch and post?
If you change the polarity of the TVS you will short the transformer winding when the blocking diode conducts.

Will this work???

thanks

Here's the design

Support please

It looks like your proposed SM6T200CA would conduct during TinySwith-III "On Time", when Bulk Voltage (Volts across C1/C2)exceeded ~200VDC (assuming 85-265VAC IN).
This would be undesirable.

I am hesitant to say it will work. I dont know what the turn of characteristics of a bi directional TVS are like when it is working like a regular diode. In the forward direction how fast can it turn on? This turn on speed needs to be less than 500 ns.
I suggest you use a unidirectional TVS and a regular high voltage fast diode.

Thanks for your replies. I have this circuit working with the SM6T200CA and the series diode (ES1J). Thanks for the explanation natb1.