L200 Variable Power Supply

Figure 1 

The circuit was designed for a power supply that can be adjusted or altered depending on the pre-set value by using a L200 volatge and current regulator.

Designing a power supply with a flexible 5-pin L200 voltage regulator makes it self-sufficient for the limits in voltage and current. It has an adjustable output current up to 2 Amp, adjustable output voltage down to 2.85 Volts, input overvoltage protection, short circuit protection, output transistor protection, thermal overload protection, low standby current drain and low bias current on regulation pin. The L200 can be used to substitute fixed voltage regulators and reduces the need to store a range of fixed voltage regulators.

The primary rating of the winding of the transformer depends on the input source but the secondary rating must generate 12 Volts running 2 Amp. Controlling the current is limited by the 47-ohm resistor while the voltage output is regulated by the 10K-ohm resistor. The circuit will produce zero voltage output if the current will go beyond the limit.

For safety purposes, all connections in the transformer should be properly insulated especially when dealing with the mains input. A plastic bobbin with 2 chambers should be used for the primary and secondary coils. No transformer is totally safe, but keeping in mind the safety ways in handling live circuits can prevent such harm.

Source:www.zen22142.zen.co.uk/Circuits/Power/l200var.html