What is 7805

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7805 Operation:

The 7805 takes in a voltage between 7 and 30 volts and regulates it down to exactly 5 volts. The first capacitor takes out any ripple coming from the transformer so that the 7805 is receiving a smooth input voltage, and the second capacitor acts as a load balances to ensure consistent output from the 7805. Transmitter circuitry consists of the following parts.

The 7805 has three leads. If you look at the 7805 from the front (the side with printing on it), the three leads are, from left to right, input voltage (7 to 30 volts), ground, and output voltage (5 volts).

                Pin diagram for 7805

Figure  – Pin Configuration of 7805

 Figure 2-22 – 7805 connection to the load

The two capacitors are represented by parallel lines. The "+" sign indicates that electrolytic capacitors are polarized: There is a positive and a negative terminal on an electrolytic capacitor. In figure 5-4, the lines from the input come in from the left. One can see the ground line of the input voltage source connected directly into the ground strip running the length of the board at the bottom. The top strip supplies +5 volts and is connected directly to the +5 pin of the 7805. The left capacitor filters the input voltage, while the right capacitor filters the +5 volts produced by the 7805. The LED connects between the +5 and ground strips, through the resistor, and lets you know when the power supply is "on."

If we measure the input and output voltage of the 7805, we would see exactly 5 volts coming out of the 7805, regardless of the voltage we input. Once we see 5 volts coming out of the regulator, we can test it further and see that it is on by connecting an LED to it. We need to connect an LED and a resistor in series. We must use the resistor or the LED will burn out immediately. A good value for the resistor is 330 ohms, although anything between 200 and 500 ohms will work fine. LED’s, being diodes, have a polarity, so if LED does not light, try reversing the leads and see if that helps. This circuit is installed is installed at the entry station, keypad station  and exit station to give them exact voltage.

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I am Kashif Mirza, the founder of Student Training Lab (STL). I am working on projects since 2005 before that I just search things and now I am sharing my knowledge through this plateform.

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Posted in: 7805 Regulator