Schottky Diode and mosfets

[Lucifre]

Why is there a schotky diode connected across a source and a drain in some mosfets?

 

[mpig09]

Dear Lucifre :

If this conidtion is used in DC-DC converter, schotky diode is used to
isolate high voltage terminal and low voltage terminal.


Please check which system that you use.


mpig

 

[chieeeeef]

Hi lucifre,

I've read a couple of articles and they indicated that the purpose of the schottky diode placed across the source and drain is to prevent the internal body diode from conducting.

Regards,

chieeeeef

 

[bunalmis]

You can connect efficent (fast / low drop) diode across to D-S, if the power lose of internal body diode disturb to you.

 

[jiripolivka]

MOSFETs are easily damaged by an overvoltage between the gate and channel. One or a back-to-back Schottky diode pair is used as a protection assuming there will be some dropping resistor connected to gate circuit.

 

[dick_freebird]

If you light up the body diode during the undershoot, its
storage time will result in a turned-on parasitic BJT when
the drain goes right-side-up. You don't want that.

 

[checkmate]

Several reasons.
1. Forward voltage of a schottky is less than that of the body diode, hence lower losses.
2. You sometimes want thermal dissipation to be redirected towards the external schottky rather than the FET.
3. During recirculation, the body diode forms forward-biased base-emitter junction of of a parasitic NPN. All it needs is to grab a "nearby" N-well on the same chip to complete a parasitic NPN.

 

[watersky]

if mos is used as half-bridge,they will work with inductor. when two mos of half bridge is off, the current continue flowing through the inductor from power or ground. this case need body diode of mos on. for the better work, schottky diode is used,parallel connect with body diode of mos.