What is TTL open collector?
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What is TTL open collector?
TTL gates with open-collector output stages have eliminated R3, Q3 and the diode, Figure 145. The collector of Q4 is connected only to the output Y. In order for open-collector TTL gates to work, an external pull-up resistor must be provided (of the order 10 k ).
How do you use an open-collector output?
With open collector output, you simply cannot just connect the output device to the pin and then to ground. Open collector does not work that way. It must have positive voltage and then the load and the negative or ground side of the load connects to the output.
Is open collector sinking or sourcing?
While the NPN open collector transistor circuit produces a “current-sinking” output, that is the NPN transistors open collector terminal will sink the current to ground (0V), a PNP-type transistor can also be used in an open collector configuration to produce what is called a “current-sourcing” output.
What is a TTL circuit?
Transistor-transistor logic (TTL) is a digital logic design in which bipolar transistor s act on direct-current pulses. Many TTL logic gate s are typically fabricated onto a single integrated circuit (IC). TTL ICs usually have four-digit numbers beginning with 74 or 54.
What is the advantage of using open-collector output in TTL logic gates rather than using totem pole output?
Totem Pole output drives the output high and low. Open collector will only pull the output low; it does not drive the output high, only releases the output to float. Multiple open collector outputs may be tied together to operate in a wire-OR arrangement, where any output may pull the output low.
Is open collector NPN or PNP?
An Open Collector output is an NPN transistor. An NPN transistor allows the sinking of current to common. It can be thought of as a switch that allows the circuit, after the load, to be connected to common. This means that a source is required for the output to work.
Does open collector need a pull-up resistor?
Open collector outputs require a pull-up resistor (R in the image above) for the output to be able to properly “output high”. The pull-up resistor is connected between the output pin and the output voltage (Vcc in the image above) that is desired for a high state.
What is the big disadvantage of open collector gates?
The drawback of open collector is high power consumption. This is because pull up resistor in the circuit uses power when the output is pulled to LOW state. This shows for required functional speed, and when the resistor value is low then the pull-up becomes stronger resulting in high power consumption.
What are TTL circuits used for?
TTL integrated circuits (ICs) were widely used in applications such as computers, industrial controls, test equipment and instrumentation, consumer electronics, and synthesizers.
What are the differences between open collector output and totem-pole output?
Totem pole operates at high speed….Difference between of Totem Pole and Open Collector :
| Totem Pole | Open Collector |
|---|---|
| Output stage of totem pole circuit consists of pull-up transistor, diode resistor and a pull down transistor. | Output stage of Open collector consists of only pull down transistor. |
Why TTL is faster than DTL?
During the transition the input transistor is briefly in its active region; so it draws a large current away from the base of the output transistor and thus quickly discharges its base. This is a critical advantage of TTL over DTL that speeds up the transition over a diode input structure.
What is open collector input?
An open collector is a common type of output found on many integrated circuits (IC), which behaves like a switch that is either connected to ground or disconnected.
