What is the difference between OD gate and OC gate? Why is there no high level at the output?

This is the OC door

 This is the OD door

 What is the difference between the two?

OC gate (Open Collector), also called open collector, is a circuit with the C collector of the transistor open;

OD gate (Open Drain), an open drain gate, is a circuit with the MOS tube D drain open.

 Principle of circuit input/output:

When the input is high, the switch is turned on, the output is pulled to GND, and the output is low.

When the input is at a low level, the switch is turned off, the output is equivalent to an open circuit, and the output is in a high impedance state.

However, please note that when the OC gate input is at a high level , the actual output here is not 0V, but should be around 0.3V. This is because the transistor has a saturation voltage drop.

When the gate input is high, the output is almost equal to 0V because the on-resistance of the MOS tube is very low.

Have any of you discovered that the circuit output can only be low level and high impedance , but there is no high level, which means that it has no driving capability for the subsequent circuit.

At this time, a pull-up resistor is needed . When the switch tube is turned on, the output is high level, and the current flows from the external VCC through the pull-up resistor to the load.

It can be understood here that the output level is determined by the power supply connected to the pull-up resistor and has nothing to do with the input level.

 However, pay attention to this pull-up resistor. Too large a resistance will affect the speed of signal switching, while too small a resistance will increase power consumption.

The recommended range is 1K~10K.

The above pictures are from "Jin Chen