i am asking about the zener diode Ds is it zener diode or not, design tips DT99-7 put a symbol of zener diode?! http://www.irf.com/technical-info/designtp/dt99-7.pdf figure 2
if it is a zener diode am i using it to keep a positive voltage difference between Vb and Vs (equal to zener voltage) to prevent negative bias?
if i use a voltage supply of 120 volt for driving the motor should the reverse zener break down voltage be greater than that as if the reverse voltage be greater than the zener break down voltage a current well flow and their is now limiting resistance to limit the current that passes through the zener diode?

 

Further down that page it states:

If a Schottky diode (Ds) must be connected between VB and VS – see Figure 4 – to avoid a negative
bias on VBS, the Schottky diode should have the following specification:
• low forward voltage drop, e.g. Vf =0.2V
• minimum 35V reverse breakdown voltage
• low reverse leakage current
• fast reverse recovery time

 

thank you for reply
in this design tips i don't know how it gonna be when Vs is equal to input voltage(high side mosfet is on) by putting the diode like that i make a path for the volt to recharge(the capacitor is charged by vcc through diode i gonna recharge it with the Vs value) the capacitor is it right?

 

.. put a symbol of zener diode?!

That is not a zener, zener has only one corner on the horizontal bar, this is a symbol for shottky diode.