LM723 Variable Power Supply with Over-Current Protection

Figure 1 

The circuit design was intended to create an adjustable power supply over a range of 1.3V to 12.2V at 1A and be able to provide protection for over-current by utilizing LM723 regulator.

• LM723 – a positive NPN standard voltage regulator mainly designed for series regulator applications which can be utilized for both foldback and linear current limiting due to its very low standby current drain circuit
• Voltage Regulator – an electrical or electronic device created for the purpose of maintaining a constant voltage level of a power source within the suitable limits
• 2N3055 – a complementary Silicon Epitaxial-Base planar NPN transistor mounted in Jedec TO-3 metal case for use as power transistor

The integrated voltage regulator LM723 will supply 150 mA of output currents but any desired load current can be provided by adding external transistors for output currents in excess of 10A. This can be used as a linear or switching regulator since its output voltage can be adjusted from 2 Volts to 37 Volts while the input voltage can be at 40 Volts maximum. The range of variations of input voltage and load current can be kept at constant using this voltage regulator.

In this design, the DIL14 plastic packaged LM723 performs with 9.5V to 40V input DC voltage while having an output voltage that is not more then 6V to 7V below the input will lead to 150 mA current source from the IC. The difference between the input and the output DC voltage plus the current is proportional to the amount power being dissipated by the transistor T1 as it accepts all the current brought by the load, thus requiring a heatsink with a heat conductive value of 5K/W. T1 is made from 2N3055 which is intended for series and shunt regulators, for output stages and high fidelity amplifiers, and for power switching circuits. The output stage of the integrated circuit will be less loaded when an external pass transistor is used which will conduct at emitter-follower mode. This will in turn cause T1 to conduct at base-emitter mode thereby producing a major resistance in the IC.

Both ceramic capacitors must be positioned closer to the integrated circuit to prevent undesired oscillations, which the LM723 is prone to, since ceramic capacitors have high frequency coefficient of dissipation. Having these capacitors directly soldered would be too much for the IC since the operating temperature of the IC is in the range of -55ᵒC to +125ᵒC.

Voltage regulators are used for several advantages in areas where uncontrolled voltage varies more than the accepted voltage of equipment which could be harmful and damaging. In motor vehicles, it matches the charging requirements of the battery and electrical load to the output voltage of the generator by rapidly switching from one to another of three circuit states using a dual pole switch loaded with spring. To keep a recommended range of voltage supplied to a consumer, regulators are used by alternating current distribution feeders or large scale power distributions or substations. This is useful in protecting the equipment using electricity by minimizing the variations in voltage. The two types of regulators being used are step regulators where the current supply is controlled and the induction regulator where an induction motor adjust the voltage by supplying a secondary which smoothens the feeder line’s current variations.

The LM723 voltage regulators are widely used for wide range of applications such as a temperature controller, a current regulator, or a shunt regulator. Also, DC power supplies in electronic equipment are using voltage regulators.

Source:zen22142.zen.co.uk/Circuits/Power/723psu.htm