The article details the process of linking typical 78XX voltage regulator ICs like 7805, 7812, 7824, etc to achieve steady regulated output voltages of 5V, 12V, or 24V. The required input voltage is a minimum of 3 V greater than the target output voltage. If a 7805 IC is utilized to obtain a steady 5 V DC output, the input DC source needs to be a minimum of 8 V DC or above, such as 5 plus 3. The regulator IC can be damaged if the maximum input DC exceeds 35 V.
Significance of 78XX voltage regulator in circuits
Different levels of voltage can lead to severe effects on a fragile electronic system. For instance, certain IC series such as TTL, LS, and HC can be easily harmed if exposed to over 5 volts.
A CMOS IC's maximum voltage is limited to 16 to 18 volts.
If a relay is used at voltages higher than its capacity, it may generate excess heat and consume electricity inefficiently.
There are a variety of additional problems that could arise with electronic circuits if an unregulated power source is used.
Numerous high-quality, easily configurable chips have been created to address the problem described above, and they are widely available at a low cost in electronic markets.
For instance, the 78XX voltage regulator series includes common voltage ratings that can be used with a regular DC power supply to produce controlled, high-quality output voltage.
Technical Specifications
Detailed information about the 78XX series integrated circuit's technical specifications.
Output voltage tolerances range from approximately ±2% at an operating temperature of 25˚C to around ±4%.
Line regulation is approximately 0.01% of VOUT/V for changes in ∆VIN with a load of 1A.
The internal components are safeguarded against overheating and excessive current.
Protections against internal short-circuit current limits are also incorporated.
These ICs also include protection for the safe area of the output transistor.
Determining the Pin Configurations of 7805/7812/7824 Integrated Circuits
In this article, a typical case is demonstrated with the use of a 7805 IC as a regulator for charging a cell phone.
In relation to the circuit diagram shown above.
These integrated circuits (ICs) only have three leads, which makes them simple to comprehend and connect. The leads are designated as input, ground, and output, in that order.
With the printed side facing you, the left lead is for input, the center lead is for ground, and the right lead is for output.
The IC is connected to the standard power supply in such a way that the positive input is connected to the input lead while the negative input is connected to the ground lead.
The result is obtained through the connection of the output and ground pins of the IC, with the positive coming from the "output" pin and the negative from the shared ground line.
Pinout Details
The majority of voltage regulator ICs that start with the 78 prefix, like the 7805, 7812, and 7824, usually have the same pinout configurations as indicated below:
Nevertheless the chart shows that apart from the 78LXX the other versions have slightly varying pinout specifications. It is crucial to connect them precisely according to the provided information to avoid the IC from malfunctioning and generating unpredictable results.
ICs that start with 78XX are positive voltage regulators that regulate a positive input voltage and provide a specified fixed voltage output across their output/Gnd terminals.
On the other hand the 79XX ICs can take in a negative voltage and generate a negative constant voltage on their respective output connectors.
The package of the ICs also indicates important information. ICs in TO220 package can handle and generate up to 1 Amp current while the smaller 78LXX version can only handle up to 100mA.
We are all familiar with the process of constructing a DC power supply circuit using a transformer, a bridge rectifier, and a filter capacitor.
Connecting four diodes in a bridge setup and attaching them to the transformer's secondary along with connecting the capacitor to the bridge terminals at the output is all that is needed.
The result generated over the capacitor is about the same as the transformer's rated voltage, slightly exceeding the transformer specifications by a few volts.
Nonetheless the voltage derived from this basic setup is not regulated or stabilized resulting in inconsistent output that fluctuates with the varying input mains voltage levels, which are always changing.
Connecting 7805, 7812, 7824 in an Electronic Circuit: A Guide
To control a current supply at a constant level, we typically utilize 78XX ICs, which can be easily linked to any power source as demonstrated below:
Application Circuit
ICs 7812 and 7824 can be similarly connected as demonstrated above, with the only variation being the input/output voltage specifications based on the IC's ratings.
An input voltage of over 13V is needed for a 7812 to generate a steady 12V at its output.
In the same way, a 7824 will need a minimum input of 26V and will provide a steady output voltage of 24V, and so forth.
What is the function of Capacitors?
Capacitors are connected to the input and output terminals of the ICs to eliminate any remaining DC spikes and ripples in the supply line.
As per the IC datasheet, the input capacitor is necessary if the input source is far from the IC, possibly more than a meter away. If enhanced transient regulation is desired to guard against noise spikes, the addition of an output capacitor is recommended.
The capacitance of these capacitors is not important, any value from 1 uF to 100 uF can be used for filtering high frequency ripples, and smaller capacitors between 0.1 uF and 0.47 uF can be added in parallel to suppress high frequency noise on the supply lines.
Steps to Obtain High Current from 7805 Integrated Circuit (up to 10 Amperes)
The purpose of a 7805 Integrated Circuit (IC) is to provide a maximum current of 1 Amp at 5 V. If you're aiming to draw over 1 amp from this IC, obtaining it directly from the IC may not be feasible.
However, this transistorized circuit not only enhances the IC 7805 specifications to provide a higher current output of up to 10 Amps, but also enables the user to obtain a voltage as high as 15 V from the 7805 IC.
The diagram outlines the process to get over 10 amps of high current from the IC 7805 and vary the output voltage between 5 V and 15 V.
High Current provided by 7805 and 7812 Integrated Circuits with Protection against Short Circuits
Here is an additional circuit that can transform a regular 7805 or 7812 integrated circuit into a circuit that delivers high current. The design also includes a feature for controlling current, which protects the output transistor from short circuits or high current overloads.
The circuit operates as follows:
Once the voltage drop across R1 reaches over 0.6 V, Q2 starts conducting and overcomes the voltage regulator IC to deliver the maximum high current from the input supply to the output terminals.
Q2 functions in a similar way to a current limiting stage. If the current going through Q1 attempts to go beyond the maximum acceptable level, the voltage drop across R2 will surpass 0.6 V causing Q2 to turn ON.
Q2 collector creates a short circuit between the Q1 base and the positive supply, preventing conduction and turning it off. This method ensures that the current is limited precisely to the intended maximum level.
The following formulas can be used to calculate R1 and R2.
R1 = 0.6 / 0.5 = 1.2 ohms 1/2 watt
R2 = 0.6 / maximum current limit
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