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Transistor as a switch: Continuously ON

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blade88

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Hello,

I want to use a transistor to act as a switch and send alarm signals.
I want the transistor to be always ON and close whenever I receive an alarm.

My question is will the transistor have any problem operating on this configuration for a long time?
I expect that it will be ON for a long time.
Can this be deduced from any parameter in the datasheet?

Thank you.
 

I want the transistor to be always ON and close whenever I receive an alarm.
Click to expand...
Normal notation is that when the transistor is ON it is conducting and OFF when it is not.
So do you mean power is applied to the transistor but it is not conducting?

Either way the transistor will operate indefinitely if it's operating well within its spec limits of voltage applied and power dissipated.
 

Go ahead. the transistor wont be having any problems unless maintained within boundary limits.
Keeping it on for the whole day wont trouble it, Calculate the base resistance according to voltage you are going to apply.
 

Hi,

blade88 said:
Can this be deduced from any parameter in the datasheet?
Click to expand...

The SOA graph is a good way of deducing whether something is possible or not.
 

Usually ok. Just want out for the average power of the transistor when it is on. That is (Vds*Ids). Every package has a power limit. Make sure it is within that limit. SOA curve is another thing to watch for. That is tied to various time duration.
 

Hi,

Just want out for the average power of the transistor when it is on. That is (Vds*Ids).
Click to expand...

and keep junction temperature below specified limit.
It is a function of ambient_temperature, power_dissipation, themal resistance..

Klaus
 

Agree. Ultimately, the junction temperature is the limit.
 

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