Current Source with two settings

In summary, John is seeking suggestions for creating a current source to switch between 10 mA and 1.4 A at a certain frequency, specifically for pulsing a laser diode. He has an idea to use a BJT transistor as a variable resistor in a LM317, but is unsure of how to do it. The suggested circuit involves using an enhancement mode MOSFET to pull current from a 5V source, with a resistor to pull 10mA when the transistor is off and 1.4A when it is on. The circuit is controlled by an op-amp, with the input determining the current sink. Heat sinks are recommended for the MOSFET and resistors, and additional components are used for stability
  • #1
jbord39
74
0
Hey all,

I am trying to create a type of current source to switch between 10 mA and 1.4 A at some frequency. I have an idea to use a BJT transistor as a variable resistor in a LM317 (or whatever the high current version is) but am not sure how to do it. Any suggestions? This circuit is to pulse a laser diode. Also, does this circuit have a name?

Thanks,

John
 
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  • #2
I make a lot of assumptions. i assume the laser diode is just a diode that has 1V drop when turn on. You have to tell me more info if I am not correct on the circuit. here is the quick I have for the first pass. I use an enhence mode MOSFET instead because I don't want to deal with the large base current and low beta that cause inaccuracy. basically I put the diode at +5V and turn it on by pulling current. I assume the turn on voltage is 1V so I use 400 ohm as R4 to pull 10mA when the transistor is off. When the transistor is on, it pull 1.4A so the 10mA just become insignificant. The circuit is a current sink control by the op-amp. The input should be 0V for turning the current sink off, 1.4V for pulling 1.4A. The accuracy depend on your requirement. You better put a heat sink on the MOSFET and the R3 because it will generate heat. R2 is to isolate the input capacitance of the MOSFET from the output of the op-amp ( that might cause instability) and C1 is to create a zero to guarante stability of the op-amp.


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1. What is a current source with two settings?

A current source with two settings is a device that is able to provide a constant current output at two different levels, typically referred to as "high" and "low" settings. This allows for flexibility in controlling the amount of current being supplied to a circuit or device.

2. How does a current source with two settings work?

A current source with two settings works by using a combination of resistors and transistors to regulate the output current. By adjusting the resistance or switching between different resistors, the current level can be changed to the desired setting.

3. What are the advantages of using a current source with two settings?

One advantage of using a current source with two settings is the ability to easily switch between different current levels without having to physically adjust the circuit or use additional components. This can save time and effort in experimental setups or in applications where variable current levels are needed.

4. What are the common applications of a current source with two settings?

A current source with two settings is commonly used in industries such as electronics, telecommunications, and research laboratories. It can be used for powering electronic devices, testing and calibrating circuits, and conducting experiments that require precise control of current levels.

5. How do I choose the appropriate current setting for my application?

The appropriate current setting for an application will depend on the specific requirements of the circuit or device being powered. Factors such as voltage, resistance, and desired current level should be taken into consideration when selecting the appropriate setting for a current source with two settings.

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