How to Build a LM317 as a Variable Voltage Regulator and Variable Current Regulator

The submit demonstrates precisely how the convenient IC LM317/338/396 can be utilized as a changeable voltage regulator as well as as a variable current regulator by means of simple configurations, employed for driving particular laser diodes which can be proven to possess strict working specs, and might be driven only by way of specific driver circuits. The mentioned LM317 design is so precise that it might be preferably appropriate for all such specialist current and voltage controlled applications.
Talking about the presented circuit diagram, the set up appears quite simple, two LM317 IC s can be viewed, one set up in its standard voltage regulator mode and the other in a current control mode.

To be accurate the upper LM317 forms the variable current regulator stage while the lower behaves like a variable voltage controller stage.
The input supply source is linked across the Vin and ground of the upper current regulator circuit, the output out of this stage goes to the input of the lower LM317 variable voltage regulator stage. Fundamentally both the phases are attached in series for applying a total quick and easy voltage and current regulation for the linked load which can be a laser diode in the present case.
R2 is chosen to obtain a range of around 1.25A max current limit, the minimum permitted being 5mA when the full 250 ohms is placed in the path, which means the current to the laser might be set as preferred, somewhere between 5mA to 1 amp.
The above is determined by utilizing the following formula:
R = 1.25/max allowed current
The current managed voltage provided from the upper stage is next placed on the lower LM317 voltage regulator circuit, which allows the most wanted voltage to be set between 1.25V to 30V, here the max range getting 9V since the source is a 9V battery. This really is accomplished by adjusting R4.
The talked about circuit is allocated to handle not a lot more than 1.5amps, if higher current is needed, both the ICs could be replaced with LM338 for getting a max 5amp current or LM396 for a max of 10amp current.