Voltage and current controller problem

Question

^{simulate this circuit – Schematic created using CircuitLab}

For a specific project , I need to create a Voltage-Current controller circuit that will be able to control the flow of Current and the voltage by using 2 different potentiometers for each.

Here is the schematic I have tried....

TIP122 Darlington for increasing and controlling current, till that it is working fine but

the IRFZ44N MOSFET part doesn't work properly for voltage regulating and I am unable to find a way to fix it.

But this doesn't seem to work.

can anyone please point me out where i have made a mistake? Explanation with circuit schematic will be much preferred and appreciated.

i need one potentiometer to control voltage and another one for controlling current

NB:

I don't want to use any types of IC for this project so please avoid suggesting one till there is another way/ways left.

Thanks for your precious time.

Answer 1

You cannot control the voltage and current in a resistor independently. That is why your circuit does not work as you intend it to.

I presume you have heard of Ohm's Law. If you apply it to your load, you will see that once you have set the voltage across the load, there is only one possible current. Voltage over resistance equals current.

If you set the current, there is only one possible voltage. Current times resistance equals voltage.

You cannot control the voltage and current in a resistor independently.

Answer 2

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Original and redrawn circuits.

The convention is that schematics are drawn with higher voltages at the top and ground at the bottom and reading left to right. That way we will generally be able to trace current flow from top to bottom and signal flow from left to right. We can also use the GND symbol to eliminate a bunch of wires to reduce clutter. Which is easier to read and understand?

Once we untangle your schematic it becomes very clear that there is no way for current to go from the 9V+ terminal to the lamp. Neither Q1 or Q2 have a positive supply connection.

If you are updating your question then please add in some explanation of how you expect your design to work.

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^{simulate this circuit}

Figure 2. OP's update.

Once we redraw the circuit with conventional layout it becomes clear that Q4 is upside down and cannot conduct to pass current to LAMP3.

Answer 3

The darlington is a "follower" with a minimum voltage loss of 1.5V. If the base is at 9V then the emitter is at most 7.5V.

The Mosfet is also a "follower" and has a wide range of voltage loss. If the gate is at 9V then its source could be as low as 4V when loaded with your 100 ohms.