Use the LT1083 to build a 7.5A voltage regulator


0

When designing the power section of any board, the most commonly used voltage regulators are 78XX, 79XX, LM317, LM337 or similar. Engineers know these controllers are safe. Reliable and easy to use, but limited for now. If you need more power, you can find simple and cheap solutions with the LT1083 Analog Devices Regulator Powerful Regulator The LT1083 regulator (see symbol and screw in Figure 1) allows you to adjust positive voltage and delivers current up to 7.5 A with high efficiency. The internal circuits are designed to operate up to 1 volt differential between input and output. The maximum dropout voltage is 1.5V at the maximum output current. A 10 uF output capacitor is required. Here are some of its noteworthy features: adjustable output voltage; Current up to 7.5 amperes; TO220 container internally limited dissipation power; Maximum differential voltage 30 volts. It can be used in various applications such as switching regulators, DC regulators, high efficiency linear regulators and battery chargers. The model examined in this tutorial features a variable and configurable output voltage. There are two other models, the LT1083-5 and LT1083-12 which stabilize the output at 5V and 12V respectively. Figure 1: LT1083 Regulator Minimum Application Diagram for a 5V Output Voltage Figure 2 shows the application diagram for a 5V regulator. The input voltage should always be greater than 6.5 V, the circuit supply voltage, of course, should not be too high, because all the power will unnecessarily run out in the heat, which will significantly reduce the efficiency of the system. The regulator is connected through its three pins to the input, output and resistor voltage divider which determines the output voltage value. It is highly recommended to have two capacitors, one at the input and the other at the output. The scheme has the function of stabilizing the output voltage at exactly 5V. For this reason, the bulkhead consists of two 1% accuracy resistors, the first being 121 ohms and the second 365 ohms. Obviously, replacing the two passive components with a trimmer or potentiometer applies a variable voltage power supply system. Figure 2: Lower but fully functional application diagram at 5-V output voltage Figure 3 shows the first measurement of the results with current on the load and power dispersed by the integrated regulator. Simulations are performed by testing different values ​​ u200b u200bof loads, with impedances ranging from 1 ohm to 20 ohms. A very important fact is the extraordinary stability of the output voltage (always exactly 5 volts) even if the load undergoes drastic changes. In fact, the current flowing through the load is very variable, along with the energy dissipated by the integrated regulator. When staying within the operating limits set by the manufacturer, the regulator is therefore extremely stable and safe. Figure 3: Measurement results on a 5-V regulator circuit The regulator is designed to operate at a “leakage” voltage of up to 1 volt. This differential is independent of the load current, and thanks to its low value, the final system can be very efficient. In Figure 4 we can see the graph of the input voltage, between 0 V and 8 V (red graph) and the output voltage (blue graph). Between the voltages there is an effective “leakage” of about 1 volt, as specified in the characteristics of the manufacturer. Figure 4: The graph of the input, output and dropout voltage The output voltage of the integrator (with the values ​​used for the resistor divider) is very stable even if a different entity load is used, as can be seen from the graph in Figure 5. Figure 5: The graph shows the stability of the output, which is independent About the load used. The efficiency is much higher as the input voltage approaches the required output voltage. The following average efficiency measurements were made using different load values, with three different power supplies, respectively at 18 V, 12 V and 6.5 V Input voltage: 18 V with circuit efficiency equal to 26.71%; Input voltage: 12 V with a circuit efficiency equal to 40.84%; Input voltage: 6.5 V with a circuit efficiency equal to 75.37%; Hence, the regulator works more when the input voltage is much higher than the output voltage, thus dissipating more energy that is lost in the unused heat. The temperature regulating effects examined in this tutorial are very stable even under temperature variations. Although the manufacturer certifies a stability of 0.5%, in official documents the results obtained are more satisfactory. Now let us examine a simple application scheme equivalent to the first examined, with the following constant characteristics: Input voltage: 6.5 V; Output voltage: 5V; Load resistance connected at output: 5 ohms; Load current: 1 A; Dissipated power by regulator: 1.51W. Now let’s run a simulation by changing the temperature in the range between -10 ° C and + 100 ° C. By examining the graph of Figure 6, we discover that over a very wide range of temperatures (110 ° C flight) the output remained practically constant. The integrated circuit is very stable and the maximum change in output voltage, at both ends of the thermostat, is only 6.2 μV. Figure 6: The diagram showing the variation of the output voltage at different operating temperatures The protective diode LT1083 regulator does not require protection diodes, as shown in the diagram in Figure 7. The design of the new component, in fact, allows to reduce return currents thanks to the use of internal resistors . Moreover, the internal diode, located between the input and output of the integrated circuit, is able to manage current peaks lasting from 50A to 100A. Therefore, even the capacitor on the regulator pin is not strictly necessary. The regulator can only be damaged if a capacitor with a capacity greater than 5000uF is connected to the output and, at the same time, the input is shorted to ground. This is an unlikely event. Figure 7: The protection diode between the output and the input is no longer necessary. How to get different tensors between the output pin and the adjusting pin, there is a reference voltage of +1.25 volts. Current flows through this resistance. The second resistor connected to the ground performs the function of adjusting the total output voltage. A current of 10 mA is sufficient to obtain this regulation in an accurate manner. By implementing a trimmer or voltmeter, a variable voltage power supply can be created. The current flowing on the regulating pin is very low, in the order of minute amps, it can be ignored. Here are the steps for calculating the two resistors, for a 14V power source, and they can be seen in the diagram of the divider in Fig.8 and the formulas shown in Fig.9: The dimensions of the input voltage Vin should always be specified at least 1 volt more than the required output voltage, so Vin> 15; There is always a voltage of 1.25V between the output pin and the reference pin; Resistance R1 must be crossed between the output and reference pin by a current of 10 mA; The value of R1 is equal to the ratio between the potential difference on the resistance and the current that it must pass through; The reference pin voltage is equal to the output voltage minus the static voltage of 1.25V; Resistance R2 must also be passed with a current of 10 mA and thus can be easily calculated using Ohm’s law. With values ​​of R1 = 125 ohms and R2 = 1275, the output voltage is exactly 14 volts. A variable power supply with a voltage between 1 V and Vin can be obtained using a 3.3 k كيلو voltmeter instead of the resistor R2. Fig. 8: Calculating the diaphragm resistances for any voltage value Fig. 9: Equations for calculating the two resistances Conclusion The LT1083 3-pin regulator is adjustable and is very easy to use. They are equipped with various safeguards that are usually provided in high performance regulators. These protection systems relate to short circuits and thermal shutdowns above 165 ° C. Exceptional stability enables the construction of high-quality power systems. A 150uF electrolytic capacitor or 22uF tantalum output capacitor is required for complete stability.


Like it? Share with your friends!

0

What's Your Reaction?

hate hate
0
hate
confused confused
0
confused
fail fail
0
fail
fun fun
0
fun
geeky geeky
0
geeky
love love
0
love
lol lol
0
lol
omg omg
0
omg
win win
0
win
Joseph

0 Comments

Your email address will not be published.