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_q12x_

1672785770820.png | ElectriciansForums.net | Free Electrical Advice - Electricians Forums: Electricians' Talk Forums

ooooh, I think I see what you mean. Sourcing and sinking the current through the transistors. I get you. Thanks !
Yes I have a ton of them, both types. Well, more bjt's than mosfets.
 
The Q outputs of the 74LS93 can only source -800 uA (Ioh) whereas they can sink 16mA (Iol) See page six at this link.

https://www.ti.com/lit/ds/symlink/sn74ls93.pdf?ts=1672895631445&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FSN74LS93

By source is meant the conventional current flow out of the pin from the +5V rail and sink is the current flow into the pin down to the 0V rail.

Or in other words, in state 1 there is a relatively high resistance connection between the Q output and the 5V rail whereas on state 0 there is a relatively low resistance connection between the Q output and the 0V rail.

One has to be careful not to draw over these current limits because as you know when a current flows through resistor it drops some voltage. Too much current drawn in the 1 state will lower the Q output voltage and too much current on the 0 state will raise the Q output voltage. If one is not careful then the voltages go out of the bands in which a 1 or 0 is declared to be present.

The 100R resistor in the collector/drain will pass a current of circa 5/100 = 50mA so check the transistors or mosfet can pass this current withoutover heating. You may have to increase the 100R resistor.

Also remember a base resistor to limit the current through the base emitter junction of the pnp transistor.

For mosfet or transistor include a 10kR between base-emitter or gate-source to reliably turn them off when the Q outputs are logic 1(high).

You will need to ensure your diode-resistor logic gates operate as AND/OR for negative logic to control each of the 16 LEDs because when a Q is high the voltage at the collector/drain with respect to 0V will be low and vice versa. This is so-called 'negative logic' so you would use an AND instead of OR and an OR instead of an AND. You may have to alter the way the LEDs are switched on/off.

Positive and Negative Logic in Digital Electronics - https://www.tutorialspoint.com/positive-and-negative-logic-in-digital-electronics
 
Last edited:
Hello,
I've --simulated-- the version with the PNPs. It works !
Of course from the 100th time but it did.
And, I can not ADD an image !!!! to show you HERE the results I got.
Ill post it in the original thread
 

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