L200-Based Voltage Regulators

Figure 1 

The circuits were designed using a single IC L200 to create two different regulators where one circuit functions as high current regulator using NPN pass transistors while the other circuit functions as programmable voltage and current regulator.

• L200 – a monolithic integrated circuit for voltage and current programmable regulation, available in Pentawatt package or 4-lead TO-3 metal case, used to replace fixed voltage regulators when high output voltage precision is required and eliminates the need to stock a range of fixed voltage regulators due to it features of low standby current drain, low bias current on regulation pin, thermal overload protection, output transistor SOA protection, short circuit protection, input overvoltage protection, adjustable output voltage and current, and blow-out proof because of current limiting and power limiting
• LM741 – a general purpose single operational amplifier with features such as offset null, compensated internal frequency, voltage range with high input, good stability of temperature, and protected from short circuit
• BC108 – an epitaxial NPN silicon planar transistor having the collector electrically connected to the TO 18 metal case
• BDW51 – a silicon epitaxial-base NPN power transistor in Jedec TO-3 metal case intended for use in power linear and switching applications

This project involves two regulators while using only one L200 integrated circuit to produce a regulator of voltage and current. From the first figure, the output voltage can be regulated with the use of 4.7K Ohms potentiometer RV1. This circuit will be responsible for handling high current values with the aid of NPN pass transistors. The second figure is constructed to regulate the output current using the 100K Ohms trimmer TR1 while the output voltage is adjusted with the use of 10K Ohms trimmer TR2.

A relatively sophisticated design is being used by the L200 and it may be used in many different configurations to provide voltage or current regulation. The resistor between pin 2 and pin 5 of the L200 is connected to control the current limiting. Typically, 0.45V is the current limit sense voltage which is variable depending on several factors including load and temperature.

The internal safe operating area (SOA) protection circuitry controls the power dissipation of the L200. As long as the input/output differential voltage is less than 20V, the device can supply a current of up to 2A. Otherwise, the maximum current output will drop greatly if the differential voltage exceeds 20V. This will cause the SOA protection to limit the current output to prevent damage to the device by reducing the power dissipation. The value of the resistors connected between pin 3 & 4 and pin 4 & 2, determines the output voltage of the device.

It is required to utilize a suitable heatsink at higher power levels to prevent the L200 from reaching excessive temperatures and the type of heatsink depends on the application. A large area of metal similar to the side of an enclosure may be already available in some cases. If the heatsink is at 0V potential, the tab of the L200 at 0V potential will be connected directly to the heatsink, but in some cases, the tab of the L200 is needed to be isolated.

Figure 2 

The use of voltage regulators using L200 IC may be found mostly in power supplies like the variable DC power supply, battery chargers, and DC-DC converters.

Source:users.otenet.gr/~athsam/L200.htm