I am confused about the implementation of an open-collector circuit. From what I've read, there are many ways to incorrectly wire up an open-collector circuit. Before I explain my confusion, let me explain how I understand the term open-collector:
My Explanation Of An Open-collector:
- The output of an IC is connected to a transistor. The base is connected internally to the circuit, the emitter is connected to ground and the collector is connected to the output pin (hence open-collector)
- Therefore, the main purpose of the IC is to sink current externally and not to source current
I've read from an article online that the proper way to implement the function of an open-collector is in the attachment of the image below:
This is basically a Quad, 2 input AND open-collector. It works and functions like a AND gate. 1A and 1B represents Input A and Input B respectively and 1Y represents the Output.
However, the textbook I am using takes a different approach as such:
This is a NAND gate. I am really confused about this implementation as it defies the truth table of a basic NAND gate. If both the inputs are high the output is HIGH, otherwise, the output remains LOW for all other inputs. This would be the traits of a typical AND gate.
I need some help clearing up my confusion as to why my textbook took that approach. Is my 74LS09 circuit configured the correct way?