question about transistor resistor logic

MikeML

Joined Oct 2, 2009
5,444
In retrospect, the 400uA makes it tough to do with a simple NPN (or with TTL or even LSTTL), I would use a 4000 series CMOS inverter.
 

MrChips

Joined Oct 2, 2009
34,809
You can get single gate components in a SMD package.

Or go with a single NPN transistor with two resistors as shown here:



The voltage source can be +5V instead of the +12V shown.
 

Thread Starter

caoadon

Joined Jul 11, 2014
24
You can get single gate components in a SMD package.

Or go with a single NPN transistor with two resistors as shown here:



The voltage source can be +5V instead of the +12V shown.
i just bought an NTE7404 hex inverter. Do i need to use resistors with them?
 

MrChips

Joined Oct 2, 2009
34,809
No need for additional resistors for your application.
You can use a single gate and leave the remaining five not connected.
If you want extra output power you can parallel multiple gates together.

400μA could be a limiting factor. Try it with one gate first and see what happens.
 

Thread Starter

caoadon

Joined Jul 11, 2014
24
No need for additional resistors for your application.
You can use a single gate and leave the remaining five not connected.
If you want extra output power you can parallel multiple gates together.

400μA could be a limiting factor. Try it with one gate first and see what happens.
It seems to be inverting fine. Do I not need to do impedance matching? THeres a 50ohm input impedance.
 

Thread Starter

caoadon

Joined Jul 11, 2014
24
Where exactly is the 50-ohm impedance?
The ultrasound im working with outputs a signal that i want to invert. so i sent it through the hex inverter. once inverted, the output of the hex inverter is the input of a laser with a 50ohm input impedance
 

MikeML

Joined Oct 2, 2009
5,444
So this is an analog signal? If so, you need a medium fast modern opamp to invert the signal while retaining its fidelity; not a logic inverter...
 

Thread Starter

caoadon

Joined Jul 11, 2014
24
Perhaps you should go into more details as to what you are attempting to do.
I am trying to invert a pulse and input it into a laser. The laser has a 50ohm input impedance.

I just bought a 7406 hex inverter open collector.
The 7404 didn't work. or it didn't invert the signal exactly (it was around a 2V pulse compared to the original 5V) because of the 50ohm impedance.
 
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