Voltage regulators (78XX series) placed in parallel.

The 78xx series voltage regulators have been discussed on the web page dedicated to them, available in this same section "experiments". We know these can deliver up to 1.5A and are protected from accidental short circuits and overtemperature. In some cases though, you need to have one stabilized voltage but with higher current intensity. On this page we see how this is possible double or even triple the intensity of current provided by a power supply that uses multiple regulators voltage placed in parallel. Connect two electrical components in parallel, such as batteries, of the same type and voltage, it allows to have double the available capacity, in terms of energy and therefore of deliverable current.

Characteristics of the L78xx voltage regulators.

The integrated of the L78xx series is a voltage regulator which, equipped with an adequate heatsink, is able to supply 1.5 A and is equipped with protection circuits against short-circuits and overheating that make it practically almost indestructible. Said regulator is produced to stabilize nominal voltages of:
5, 5.2, 6, 8, 8.5, 9, 10, 12, 15, 18, 24 V.

To consult all the electro/mechanical characteristics of the positive voltage regulator, download the datasheet clicking on the pdf icon

Below is the wiring diagram with the components necessary for the construction of a power supply based on the regulator voltage at 12V, capable of delivering up to 3A.

Description

As can be seen from the wiring diagram, to double the current that can be supplied by a power supply that uses regulators voltage, you need to connect two in parallel. Remember that to allow the regulator to stabilize the voltage at its nominal value, the input voltage must be at least 2V higher than the latter. For example, and in our case, the voltage to be applied to the L7812 regulator must be at least 14V DC. The maximum voltage, indicated in the component datasheet, is 35V. For a good functioning of the However, it is highly recommended that the input voltage be higher than but as close as possible to 14V. The reason for this lies in the fact that unused energy is dissipated in the form of heat according to the following formula: (V_in - V_out) * I. For example: with an input voltage of 14V and one absorbed current of 1.5A we will have a power converted into heat of (14-12) * 1.5 = 3W, while with a voltage of 25V we will have (25-12) * 1.5 = 19.5W. In cases like the latter, the regulator must be fitted of a generously sized heat sink to the detriment of miniaturization and especially energy efficiency. Returning to our circuit, since the regulators are not exactly identical (even if from the same manufacturer) to the output of it is advisable for each regulator to follow a rectifier diode of at least 2A in order to prevent any current of recirculation. However, this expedient introduces an output voltage drop with a characteristic value of approximately 0.7V. For compensating for the voltage drop introduced by the aforementioned diodes, the regulators are forced to stabilize a higher voltage to the nominal value of the same value as the voltage drop by inserting another rectifier diode between the ground of the regulators and the general ground of the circuit.