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7809 Voltage Regulator – Complete Guide

Delivering just the correct voltage is one of the most critical demands in any electronic circuit. Thus, an ideal voltage regulator should easily convert the input voltage to the desired output. So how do we ensure that external components receive a constant voltage? A linear voltage regulator is a solution. In this article, we'll analyze the operation of a 7809 voltage regulator. Thus, check out this article to elaborate on voltage and output current.


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What is a 7809 Voltage Regulator?


A Voltage Regulator in a Box

Figure 1: A Voltage Regulator in a Box


The 7809 voltage regulator is a linear regulator. It can convert an input voltage of between 11V to 35V of DC power supply. Also, note that the L7809 voltage regulator will produce a fixed output of 9V at a current of 1A. Additionally, it can deliver a surge current of up to 2.2A. 

Note, this voltage regulator does not necessarily require external components to function. Also, as it delivers fixed voltage, consider it as a fixed-voltage integrated-circuit voltage regulator. Therefore, some refer to it as a 9V voltage regulator. 


7809 Pinout Configuration


Voltage regulator Close up on a White Background 

Figure 2: Voltage regulator Close up on a White Background 


7809 Pinout only features three pins, as illustrated in the table below. 

Pin Number Pin Name Explanation
Pin 1 An input pin (V+) The unregulated input voltage enters the IC via this pin. 
Pin 2 Ground pin It connects the IC to the ground
Pin 3 An output pin It provides the regulated +9V constant output voltage.

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7809 Features and Specifications


Electrical Supplies

Figure 3: Electrical Supplies


The following are some of the key features and specifications of the IC

  • Firstly, It has a maximum input voltage of 35V, and the minimum input voltage is 11V.
  • Secondly, the typical output current of the IC is 1A, and It features a peak surge current of 2.2A.
  • The IC delivers a fixed output voltage of 9V +/- 4%; its drop-out voltage (VI – VO) is 2.0V.
  • Also, it's available in a TO-3, TO-220, and KTE package.
  • The Ripple rejection or PSRR  of the IC is 55 dB
  • It features short circuit current limiting protection and an internal thermal regulation mechanism.
  • Finally, Its maximum junction temperature is 125 degrees centigrade.


Power Dissipation of a 7809 Voltage Regulator


A Technician Working on an Electrical Appliance

Figure 4: A Technician Working on an Electrical Appliance


So why the 7809 voltage regulator instead of the conventional DC-DC converters. While both serve the same purpose, a 7809 voltage regulator is more effective. Note, it outputs little ripples as compared to the DC-DC converters. 

Nonetheless, the 7809 voltage regulator has the disadvantage of dissipating more heat. 

Another fundamental feature is the presence of a series pass transistor on the output. Essentially, it facilitates the process of dropping the circuit's excess voltage. Also, note that power dissipation = (input voltage - output voltage) x output current.

The example below shows how to calculate the power dissipation. 

Example: Consider a 7809 voltage regulator with an input voltage of 12V and a current of 1A. 

Solution: Note, the output voltage is constant at 9V. Thus, the power dissipation of the circuit= (12V-9V) x 1A = 3Watts. 

Typically, the voltage converter can dissipate a maximum of 1.25Watts without requiring a heat sink. Hence, you'll need a heat sink in the circuit in our case. 


7809 as +9V Voltage Regulator


A Ceramic Capacitor

Figure 5: A Ceramic Capacitor


The typical application circuit of the IC is a +9V voltage regulator. The IC requires two capacitors of 0.33uf and 0.1uf to function. Note the 0.33uF input capacitor should ideally be a ceramic in this circuit in this circuit. Thus, it will prevent input impedance that is synonymous with such courses. 

Also, the 0.1uf output capacitor should be a ceramic capacitor type. Primarily, a ceramic capacitor will significantly improve the circuit's capacity. It will be imperative in enhancing the operation of the course. Also, during connection, ensure you place the capacitors near the terminals.

Additionally, avoid using electrolytic capacitors in the place of ceramic capacitors. Ceramic capacitors are faster thus are ideal in such a circuit. 


7809 Voltage Regulator Applications


  • It's vital as an adjustable output and polarity-reversal-protection in electronic circuits
  • As a current limiter in several applications, it also powers microcontrollers and sensors.
  • It delivers a regulated dual supply of current




As you have seen, a 7809 voltage convertor is simplistic in operation. Yet, it is capable of delivering a constant output voltage of 9V. We have also covered the critical uses of the voltage converter. There are many other applications, including in your simple electronic project. 

If there are grey areas about the voltage convertor you'd like us to clarify, reach out. We'll respond promptly and answer all your queries.



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