Open-drain and push-pull output
Digression: I just realized that my digital and analog electronics are so slag! ! !
Summarize the characteristics of open-drain and push-pull output on the Internet, and let those who need it understand together.
Push-pull output:
Let's first understand the principle of the next triode. pnp and npn, the triode has three ports, including the base (base), the collector (collector), and the emitter (emitter).
NPN transistor
This kind of triode is a current-controlled component, as long as the base has input or output current, the transistor can be controlled.
When the base B has current input, the current will enter from the Q1 terminal and flow out from the emitter E.
PNP transistors are just the opposite
Push-pull circuit:
the upper transistor is an N-type transistor, and the lower one is a P-type transistor.
When the Vin voltage is V+, the upper N-type transistor control terminal has a current input, and Q3 is turned on, so the current passes from top to bottom, providing current to the load. The current is supplied to the load (Rload) through the above N-type transistor, which is called "push".
When the Vin voltage is V-, current flows out of the lower transistor, Q4 is turned on, and current flows from top to bottom through the lower P-type transistor to provide current to the load (Rload), which is called "pull".
Above, this is the push-pull circuit.
Open- drain:
Understand the open collector,
as shown in the figure, the meaning of the open collector, that is, the collector C end is not connected to anything, and it is directly used as the output port.
If you want to use this circuit with a load, such as an LED, you must connect a pull-up resistor, like this.
When Vin has no current and Q5 is disconnected, the LED is on.
When Vin flows into the current and Q5 is turned on, the LED turns off.
The open-drain circuit is to replace the transistor in the above picture with a field effect transistor (MOSFET).
The FET is a voltage-controlled component. As long as a voltage is applied to the gate, the DS will be turned on. A characteristic of the junction field effect transistor is that its input impedance is very large, which means: no current flows from the control circuit, and no current enters the control circuit. With no current flowing in or out, it won't burn out the control circuit. Unlike bipolar transistors, they are current-controlled components. If an open-collector circuit is used, the control circuit may be burned out.