load circuit

[Alex QW]

Hi all,

May I know how this TTL load circuit work as shown in the below diagram?

Note that: 1)the red arrow means the microcontroller control signal (1,2)
                2) Is the TTL output pin (3,4)

The circuit is in this link: https://forum.allaboutcircuits.com/threads/ttl-load-circuit.192516/

Thank you.

Best Regards
Alex.

[Terry Bites]

Erm. I'm not registering with your website.
You didn't give out any information on your circuit there either!
A TTL load is an equivalent circuit of a TTL gate input.
Have a look at the TTL wiki page.
see www.interfacebus.com/Glossary-of-Terms-TTL-Load-Circuits.html

[Alex QW]

May I know why they use a lot of diodes in the circuit?

[Kim Christensen]

Attach the picture of your circuit here. Most people can't see it on allaboutcircuits.com since we don't have an account.

[Alex QW]

This is the circuit diagram


 Note that: 1)the red arrow means the microcontroller control signal (1,2)
                2) Is the TTL output pin (3,4)

Sorry for any inconvenience as I just joint this forum not so familiar with this feature

[Terry Bites]

The bias resistors set up a current (1.2mA) in the diodes going to ground- this sets VIL for the equivalent gate input plus a diode drop. You then subtract a diode drop ((D604)  from this voltage.
This sets the lower threshold to a bit over VIL.

[Alex QW]

how to know that the bias resistors set up a current (1.2mA)?