Why should a Schottky diode be connected in parallel to the resistor?

[hannover90]

Why schould a Schottky diode be connected in parallel to resistor?

In some over voltage (or spikes) protections, a Schottky diode is used, which is connected in parallel to a resistor.
I can not understand the role of the resistor.

Could someone explain to me, please? Thanks

 

[crutschow]

Re: Why schould a Schottky diode be connected in parallel to resistor?

That's not a typical connection.
Show an example circuit doing that.

 

[barry]

Re: Why schould a Schottky diode be connected in parallel to resistor?

In some over voltage (or spikes) protections, a Schottky diode is used, which is connected in parallel to a resistor.
I can not understand the role of the resistor.

Could someone explain to me, please? Thanks

Without seeing your schematic it's impossible to answer. Maybe you've got a diode placed across a resistor, rather than the other way around.

 

[hannover90]

Re: Why schould a Schottky diode be connected in parallel to resistor?

Without seeing your schematic it's impossible to answer. Maybe you've got a diode placed across a resistor, rather than the other way around.

Thanks for your reply.
In the attachment is an example of a driver with two schottky diodes for an over voltage protection.
I understand, how the schottky diodes work but I can not understand, why should resistors be connected to these diodes.

 

[FvM]

Re: Why schould a Schottky diode be connected in parallel to resistor?

The resistors may serve a purpose if the driver is tri-stated.

 

[hannover90]

Re: Why schould a Schottky diode be connected in parallel to resistor?

Thanks for your answer.
Because of parasitic effects, the spikes appear on Vout.
The Schottky diodes prevents the negative [spikes < (0 V-VD of Schottky] and positive spikes [spikes > (VDD+ VD of Schottky].
But which role has resistors??

 

[dick_freebird]

Re: Why schould a Schottky diode be connected in parallel to resistor?

At best they might be a shunt termination meant to
match a transmission line characteristic impedance.

At worst they are just a stupid illustration that only
burns static power.

 

[barry]

Re: Why schould a Schottky diode be connected in parallel to resistor?

I like FvM's answer. The resistors will hold the output voltage at half the rail if both FETs are off.

 

[crutschow]

Re: Why schould a Schottky diode be connected in parallel to resistor?

......... Maybe you've got a diode placed across a resistor, rather than the other way around.

How are those two different other than semantically? :???:

 

[ftsolutions]

Re: Why schould a Schottky diode be connected in parallel to resistor?

Given that the resistors are the same value, a practical use would be for trying to match a characteristic impedance. If they were different values, I'd suggest it would be for the output
to be at a specific DC bias when the driver is not being driven (tri-stated). The diodes could in most cases accomplish the midpoint-level bias point by themselves, depending on current requirements.

 

[barry]

Re: Why schould a Schottky diode be connected in parallel to resistor?

How are those two different other than semantically? :???:

It's also functionality. If you're trying to limit a voltage across a resistor, you'd put a diode across it. The op asked 'why put a resistor across a diode'. It's the same difference as putting a house under a roof.