Why is pull up resistor needed for an open collector gate?

Why is pull up resistor needed for an open collector gate?

A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. Some open-collector gates, such as the 74LS06 are capable of driving larger loads because their outputs can be connected to supplies of up to 30 volts via an external pull-up resistor.

Why would use an open collector TTL IC?

When do we use open collector TTL gate? – Quora. TTL outputs are strongly pulled up and down. This simply means you can not connect two outputs together where this is a possibility of one output set as high and another as low. This can damage the parts.

Can a TTL gate drive an LED without an external pull up resistor?

The gate will not function properly without the external pull up resistor. Thus the gate is only ever used to sink current, and so can be optimized for that function. An example of this in use is to drive an output device like an LED which may require more current than normally provided by a TTL gate, as in Figure 4.6.

How is it different from open collector TTL?

In case of open collector we only have pull down transistor and it operates at slow speed. Open collector behaves like a switch in which it is either connected or disconnected in an Integrated circuit. Output stage of totem pole circuit consists of pull-up transistor, diode resistor and a pull down transistor.

What is the value of external pull-up resistor in 8051?

When the switch is open, the microcontrollers input would be floating and brought down only when the switch is closed. A typical pull-up resistor value is 4.7kilo Ohms, but can change depending on the application.

Can a TTL gate be connected to a pull up resistor?

Two or more open-collector outputs of TTL gates can be directly connected together and tied through a single external pull-up resistor. The result is that the outputs are effectively AND’ed together as the combination behaves as if the gates were connected to an AND gate. This type of configuration is called wired AND logic.

Why do I need a pull up resistor for open collector?

Open Collector Output pins should be tied to a valid logic level so the output remains fixed at a valid voltage level when the device turns off. Wire AND-ing requires a pull-up resistor which needs to function for the range of devices tied to the wire-AND.

Can a open collector output go up to 12 V?

It is true that in conjunction with a pull-up resistor, the open collector output can go up to 12 V, but that’s assuming that there is only minimalcurrent draw from that 12 V output. The issue is that the open-collector output does not source current at all; it only can sink current.

How does a pull up resistor work in a logic gate?

With a pull-up resistor connected, the output still works in the same way as a normal logic gate in that when the output transistor is OFF (open), the output is HIGH, and when the transistor is ON (closed), the output is LOW. Thus the transistor turns ON to pull the output to a LOW level.