Usually, the resistance of the load automatically limits the current through the transistor. Only in special cases do you need to have a secondary current limiter. Adding resistance in the emitter circuit of a transistor is one method.I am trying to learn how to limit the current flow through a transistor or mosfet some direction will be greatly appreciated.
Quite a few:I am trying to learn how to limit the current flow through a transistor or mosfet some direction will be greatly appreciated.
I am using a LM317 in my circuit to provide a regulated voltage of 18 volts to my circuit. The output goes to the base of a TIP41 which I hoped would regulate the current.Usually, the resistance of the load automatically limits the current through the transistor. Only in special cases do you need to have a secondary current limiter. Adding resistance in the emitter circuit of a transistor is one method.
Give a us a specific case?
This idea has come up in other threads on small audio amplifier design. What you show is called dangle biasing, and produces inconsistent results. The current gain of a transistor changes based on base current, collector current, temperature, Vce, and of course from one device to another. While starving the base will indeed limit the collector current, it is the least consistent and repeatable way to do it.View attachment 91762
Here's something I used to limit the current from a car battery to an alternator come brush-less motor I was playing with.
Don't do that. You cannot put all of that current through the base of that poor little transistor.I am using a LM317 in my circuit to provide a regulated voltage of 18 volts to my circuit. The output goes to the base of a TIP41 which I hoped would regulate the current.
The TIP is getting so hot that the heatsink dis colours and burns the PCB
How do I achieve the regulated voltage of 18volts and a current limit of 2 ampsDon't do that. You cannot put all of that current through the base of that poor little transistor.
Do you need 2 amps or do you need 18 volts? Your LM317 can be wired as a constant current source. Check the datasheet. There is a 1.25v drop from out to adj pins. Add a o.68 ohm resistor across those two pins and take the power out from the adj pin (don't connect that pin to anything else. Obviously, you still need your input (+) to the in pin. The load connects between ADJ and (-) power (ground).
Note, the 0.68 ohm resistor should be 2 amps x 2 amps x 0.68 ohms = 2.8 watts (round up to 3 or 5 watts).
Cheers
To get both, you need to regulate the voltage to exactly 18 volts and then add a load of 9 ohms.How do I achieve the regulated voltage of 18volts and a current limit of 2 amps
Is your load constant or variable?How do I achieve the regulated voltage of 18volts and a current limit of 2 amps
the load is variableIs your load constant or variable?
by Aaron Carman
by Jake Hertz
by Jake Hertz
by Aaron Carman