Excessive output current of mA without external pass transistor. Better Input supply voltage of maximum 40v. Provide adjustable output from 3v to 37v. Used in making linear or switching regulator. Able to provide 10A of output current with use of external pass transistor. Used for various operation like positive supply, negative supply, series, shunt, and floating.
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Datasheet Voltage regulators are used to getting a stable fixed output voltage. LM IC is also a voltage regulator but it can generate a variable voltage which can be adjusted in a range of 3V to 37V. It is basically used in the series regulator application. Although it offers a mA output current. But we can get an excessive current of up to 10A for driving the load by connecting a bypass transistor externally. The maximum input voltage supply is 40V.
But the pin layout is the same for all packages. This picture shows a pinout diagram with brief details of each pin. Pin 2 is connected to the base of the transistor internally. Therefore, pin 2 is used for limiting the current. Pin 4 is the inverting input of this amplifier. It is used for obtaining constant voltage at the output by providing output voltage as a feed back to this pin.
A reference voltage is applied at this pin. Pin Vref It is the output of the voltage reference amplifier integrated inside the IC. It provides an output voltage of approximately 7V. Pin V- Connect this pin with a ground of the circuit. Pin Vz This pin is used in designing negative voltage regulators. It is connected to the anode terminal of the Zener diode.
Pin Vout It gives the regulated output voltage in a range of 2V to 37V. Pin Vc It is connected to voltage supply when it is not connected to a series pass transistor. Otherwise, it is connected to the collector of the series pass transistor. We can connect maximum of 40 volts input to this pin. Internally, it is the output pin of the error amplifier.
LM Voltage Regulator Features The important features of this IC are: It is an adjustable voltage regulator which operates in both positive or negative supply operation. Voltage can be adjusted from 2V to 37V. The maximum input voltage is 40V. Output current is mA without an external pass transistor. It can be increased to 10A by adding transistors externally.
It has a low standby current gain, very low-temperature drift, and high ripple rejection. The load and line regulation is 0. It has a built-in fold back current limiting. Where to use it? Due to its small size and lower cost, it is used in a wide variety of applications. It can be used as a series, shunt, linear, switching and floating regulators.
Its wide voltage range, low noise, and extreme flexibility make it highly suitable for use in series voltage regulation applications. This voltage is then fed back by connecting a resistor and a capacitor to the non-inverting pin of the IC. The two voltages at the inverting and non-inverting pin are compared. If the voltage at pin5 is greater than pin4 then the current will flow from the collector to emitter of a series pass transistor and we can get the output voltage.
Simple Application Circuit To adjust the output voltage value, you can replace R1 with a potentiometer. By varying the resistance of that potentiometer, you can achieve the desired output. But the only issue with this circuit is low output current that is mA.
LM Example Circuits In this section, we provide some practical examples using this variable voltage regulator. However, we can increase the current limit up to 10 Ampere by using external transistors. It will provide a constant voltage at the Vref pin. After that, we connect the Vref voltage to the noninverting pin through the variable resistor and capacitor circuit.
It can provide 1 Ampere output load current. We use a pin DIP package. After that 1N diodes based full bridge rectifier converts ac voltage into dc. Capacitors C1 and C2 removes ripples from dc voltage and provides smooth dc voltage to LM A variable resistor of 10k shown with the name of 10k POT is used to adjust output voltage. Linear, switching and floating regulators Series and shunt regulators.
LM723 Variable Voltage Regulator