How to control this latch with Positive Logic

digital-logiclatch

Here is a simple 2 transistor latch circuit controlled with 2 switches to ground. How can I control this using 3-5 volt sources instead of switches?

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Best Answer

To control the circuit with positive logic, replace each of the switches with a general purpose low power transistor like shown in the circuit below.

schematic

simulate this circuit – Schematic created using CircuitLab

If your input is fed from more than 5V power supply, you may consider increasing R1. Eg. 2k7 for 12V-15V.

The circuit may very well work with higher resistors, but you didn't spec any currents/resistors in yours so I have to be on the safe side.

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