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- Oct 6, 2021
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Hey everybody. So I want to use a mosfet to turn off my screen using the HPD pin on my HDMI-out port. Been looking into it for a while and still pretty confused on some of the terminology and what exactly I should be searching for on Digikey to find an appropriate mosfet to use. I've drawn up a rough schematic for what I think I need here:
I'm pretty sure I want a pull-down resistor on the gate so that it's normally at 0v when no HDMI cable is plugged in. Then it would get pulled up to 5v when and HDMI cable is plugged in. I'm also pretty sure I want a p-channel mosfet for this so that when the gate is 0v there will be current flow between the source and drain. A little confused on what to input in the digikey filters to find this, specifically stuff like "Vgs (Max)" and "Vgs(th) (Max) @ Id".
Also a little confused looking at some of the datasheets. Take this one for example:
This is a P-channel mosfet.
1: Does this mean that when the voltage of the gate pin is somewhere between 0.5 and 0.9 Volts less than the voltage of the source pin that this would be considered "ON"?
2: What does "ON" mean in regards to a p-channel mosfet? That there IS current flowing from source to drain, or that there IS NOT current flowing from source to drain?
3: And if "ON" means that the gate pin is between 0.5-0.9v less than the source pin, what voltage do I need for it to be considered "OFF"?
Does it need to be greater than 0.9V less than source, eg: Gate = 0V, Source = 5V.
Or should it be less than 0.5v, eg: Gate = 4.9V, Source = 5V.
(Hope that makes sense)
Any help checking on my schematic, or finding a mosfet, or helping me understand this better would be greatly appreciated!
Edit: I was able to figure this out. That Gate Threshold Voltage really threw me for a loop but I've got it, tested it, and it works. All good.
I'm pretty sure I want a pull-down resistor on the gate so that it's normally at 0v when no HDMI cable is plugged in. Then it would get pulled up to 5v when and HDMI cable is plugged in. I'm also pretty sure I want a p-channel mosfet for this so that when the gate is 0v there will be current flow between the source and drain. A little confused on what to input in the digikey filters to find this, specifically stuff like "Vgs (Max)" and "Vgs(th) (Max) @ Id".
Also a little confused looking at some of the datasheets. Take this one for example:
This is a P-channel mosfet.
1: Does this mean that when the voltage of the gate pin is somewhere between 0.5 and 0.9 Volts less than the voltage of the source pin that this would be considered "ON"?
2: What does "ON" mean in regards to a p-channel mosfet? That there IS current flowing from source to drain, or that there IS NOT current flowing from source to drain?
3: And if "ON" means that the gate pin is between 0.5-0.9v less than the source pin, what voltage do I need for it to be considered "OFF"?
Does it need to be greater than 0.9V less than source, eg: Gate = 0V, Source = 5V.
Or should it be less than 0.5v, eg: Gate = 4.9V, Source = 5V.
(Hope that makes sense)
Any help checking on my schematic, or finding a mosfet, or helping me understand this better would be greatly appreciated!
Edit: I was able to figure this out. That Gate Threshold Voltage really threw me for a loop but I've got it, tested it, and it works. All good.
Last edited: