OR Gate Circuit: What is the Function of Diodes?

  • Thread starter Kolahal Bhattacharya
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In summary, the function of the diodes in an OR operation standard circuit is to isolate the inputs from each other and protect the electronics from shorting. They are also necessary for proper functioning with toggle switches and LED indicators. Using diodes or open collector ICs with external resistors is the recommended practice for TTL wired OR connections.
  • #1
Kolahal Bhattacharya
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I don't like electronics at all.However,it's an interesting question.For OR operation standard circuit,there are two diodes which are forward biased in 1-1 state.I cannot draw the circuit here;but anyone familiar to the circuit undearstands that even if the two diodes were not there, the OR operation could be performed.Then what is the function of those diodes?
 
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  • #2
The diodes have to be there otherwise the inputs are not isolated from each other. This may be fine when using toggle switches, but suppose you have two toggle switches and each one has an LED indicator on it's output. The outputs of the switches are then wired together in OR fashion without diodes. Whenever EITHER switch is thrown both LEDs will light up.
 
  • #3
'Nova's got it exactly right. Sometimes these so-called "wired or" connections are fine, but it is generally bad practice

The diodes are also there to protect your electronics. For example, in TTL you represent a logic "0" with a ground connection and a logic "1" with a +5V connection. What would happen if you had a 1-0 connection? You've just shorted your +5V rail to ground! Hope you built in some over current protection!
 
  • #4
mdelisio said:
'Nova's got it exactly right...

That's Averagesupernova to YOU buster!
-
I have to pick on the newbies a bit. :wink: Welcome to PF!
 
  • #5
The TTL wired OR used open collector ICs with an external resistor for pullup.
No problem with shorting the +5 rail to ground.

Some of the old 74xx TTL ICs with active pullup could tolerate the cross state condition.
While it was bad practice as stated, I've seen it done.

Max toggle rate is somewhat lower without active pullup.
Same goes when using diodes.
 

1. What is an OR gate circuit?

An OR gate circuit is a digital logic circuit that has two or more inputs and one output. The output is high (logic 1) if at least one of the inputs is high, and it is low (logic 0) only if all inputs are low.

2. How does an OR gate circuit work?

An OR gate circuit works by using diodes to connect the input signals to the output. When any of the inputs are high, the diodes allow current to flow to the output, making it high. If all inputs are low, no current can flow through the diodes, and the output remains low.

3. What is the role of diodes in an OR gate circuit?

Diodes in an OR gate circuit act as switches that control the flow of current to the output. When the input signal is high, the diode will allow current to flow through to the output, and when the input is low, the diode will block the current.

4. Are diodes the only components used in an OR gate circuit?

No, diodes are not the only components used in an OR gate circuit. Other components, such as resistors and transistors, may also be used to improve the performance and stability of the circuit.

5. What are the applications of OR gate circuits?

OR gate circuits are commonly used in digital electronics to combine multiple binary inputs into a single output. They are also used in many electronic devices, such as computers, calculators, and remote controls, to control the flow of information and signals.

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