Regulators provide a power source which remains very close to a fixed value, independent of the load placed on it, provided that the current drawn doesn't exceed the rating of the device. Note: The minimum and maximum output voltage specifications for fixed voltage regulators indicate the values which can be expected with variations in load on the device. The same specifications for adjustable regulators indicate the range of voltage output which can be achieved through external componentry.
Basic 1A regulated circuit with fixed regulator
The 78xx series of voltage regulators require the input pin to be at least 2.5 volts above the output voltage. When a bridge rectifier is used, the DC voltage before the regulator is going to be 1.414 x the AC secondary voltage of the transformer. For good regulation ensure that there is at least 3 volts on the input pin over and above the output voltage of the regulator. Note the maximum input voltage to the regulator should not exceed 35V.
Boosting current output of voltage regulator
When more than one amp of current is required there are a number of options available. One way is to put in a more expensive higher current regulator and the other is to boost the one amp device with a bypass transistor. The following circuit shows the necessary configuration to boost the output to 4A.
Basic voltage regulator using LM317T or LM350T
When a variable power supply is required, this circuit is an ideal solution. The diodes are not essential but are recommended to give short circuit protection. The maximum input voltage to the regulator should not exceed 40V.
Current boosted regulator using LM317T or LM350T
This circuit provides a high current capacity variable power supply, delivering 1.2 to 37V at up to 4A. Note the addition of the bypass transistor. Once again the maximum input voltage to the regulator should not exceed 40V.
