Any other circuit configuration that will work?

Maybe you can find a readily made buck-boost module that can do the voltages you want though finding one that goes up to 7A might be difficult.

 

how would one do a 3V dropout then?

3V out from 6V in.

 

how about this circuit?
I also like to know how it works.

 

how about this circuit?
I also like to know how it works.

View attachment 324173

Exactly the same way, but not quite so accurate.
The 2n3904 and 1N757 take the place of the TL431. The TL431 is a much better reference than the 1N757.

It also has a current limit: R4 takes the place of Rb, but is has Q1 in series. If the voltage drop across R5 exceeds the voltage across D2, Q1 is switched off which in turn switches off Q4.

 

Exactly the same way, but not quite so accurate.
The 2n3904 and 1N757 take the place of the TL431. The TL431 is a much better reference than the 1N757.

It also has a current limit: R4 takes the place of Rb, but is has Q1 in series. If the voltage drop across R5 exceeds the voltage across D2, Q1 is switched off which in turn switches off Q4.

They way I am analyzing:
Intially:
D2 and D3 cause Vin-1.7 voltage at base of Q1. Voltage at R5 terminals are: Vin, Vin-1.7. At R4 one end it is vin-1.7+.7.

After that I am lost as to what the voltage is at R4 terminal facing the base?? I am also not sure if Q2 is on or off?

 

They way I am analyzing:
Intially:
D2 and D3 cause Vin-1.7 voltage at base of Q1. Voltage at R5 terminals are: Vin, Vin-1.7. At R4 one end it is vin-1.7+.7.

After that I am lost as to what the voltage is at R4 terminal facing the base?? I am also not sure if Q2 is on or off?

Assume 0.6V for the voltage across a silicon diode, so Q1 base is at Vin-1.3V
Voltage across R5 is the current through it multiplied by its resistance.

 

Assume 0.6V for the voltage across a silicon diode, so Q1 base is at Vin-1.3V
Voltage across R5 is the current through it multiplied by its resistance.

Well
What exactly is the current thru R5?
What exactly is current thru R4?

 

Well
What exactly is the current thru R5?
What exactly is current thru R4?

What do you think it is? Referring to your previous circuit.

 

What do you think it is? Referring to your previous circuit.

If i had to guess R4 20ma and R5 would be 200 mA?? I am not sure you use hfe to calculate based on load current but i am not sure if q2 is on or off initially.

 

If i had to guess R4 20ma and R5 would be 200 mA?? I am not sure you use hfe to calculate based on load current but i am not sure if q2 is on or off initially.

Assume that it is operating as a regulator, and you have a load connected.

 

Assume that it is operating as a regulator, and you have a load connected.

Can you help? I just dont know where to begin. Whatever I am thinking and getting stuck at i posted. R4 20ma and R5 would be 200 mA??

 

Here's how You can help everybody concerned.
Start with a description of the major Components that You intend to employ,
and the performance that You expect from these individual devices.

Simply giving a list of Voltage and Amperage numbers does not tell the whole story.

A Specification PDF for each major device would be ideal.
Then we can intelligently discuss the practicality of your expectations,
and what other routes might be feasible in the quest of obtaining your desired performance.
.
.
.

 

Can you help? I just dont know where to begin. Whatever I am thinking and getting stuck at i posted. R4 20ma and R5 would be 200 mA??

I can help, but you also have to think, because I won't always be here when you get stuck.
You have a regulator, with a load connected and current is flowing in the output.
What path is that current taking to get from the input to the output? Which components does it go through?

 

Well
What exactly is the current thru R5?
What exactly is current thru R4?

You implied that you knew how to use LTspice. Why are you asking these basic questions? If you can't figure out how a circuit works using a circuit simulator, you're going to have a hard time with circuits.

 

You implied that you knew how to use LTspice. Why are you asking these basic questions? If you can't figure out how a circuit works using a circuit simulator, you're going to have a hard time with circuits.

In LTSpice can I see initial how it calculating everything? How and where is that file?

I am new sorry

 

You implied that you knew how to use LTspice. Why are you asking these basic questions? If you can't figure out how a circuit works using a circuit simulator, you're going to have a hard time with circuits.

Goes thru R5 and then to Q2?? Please help

 

Goes thru R5 and then to Q2?? Please help

Right, so what is the voltage across R5?

 

Goes thru R5 and then to Q2?? Please help

Why do you keep asking questions LTspice can answer?

R5 determines when current limiting is enabled (by taking base current from the pass transistor).

 

Right, so what is the voltage across R5?

0.7V?

 

In LTSpice can I see initial how it calculating everything? How and where is that file?

I am new sorry

I suggest you return to your original two questions. For this I can show you a method to derive an equation from a array of voltage / current values.

It starts by getting the simulation set up with real world components. Try several TL431 models as well as many BJTs. Take advantage of the spice directive feature which allows you to program your own model from scratch.

Next run one or more types of simulation (transient, ac, etc.) and save the output as raw data to a text file. It's most obvious to plot voltage / current but you can plot anything (voltage / voltage or current / temp etc.).

Once the data is in a raw format, use ChatGPT or a similar tool to "find a pattern or equation" in the data. Tell it to output the result as a graph or in algebraic form. This method works surprisingly well for basic data-sets and you can get a long way with it. Of course you should be learning Kirchoffs laws as well but this allows you to derive independent equations based on arbitrary data.