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Hi everyone,

Not sure if this is the right place to post this, but I would like some help with my circuit here:

The intent is to charge a battery based on a 5V input signal, simulated with V3. There are a lot of problems with the circuit, and I really don't know what I'm doing. The biggest problem seems to be that the current through J3 is too large. I think I need some other power transistor in there, but I couldn't make a circuit that would work.

Any suggestions?

I'm really not sure how you intend this circuit to control charging, but certainly the JFET cannot be controlled if Q2 pulls down but there is no opposing pull-up. A resistor from Q2 collector up to a more positive node (U1 OUT pin, IN pin, or the 24V input) would at least allow the FET to be driven with a wide range of gate voltages.

As a practical matter, why use an external Q1 rather than processing the power with the LM317? The regulator is inherently current and temperature limited, making the system pretty hard to blow up. Q1 looks to have high V and high I simultaneously, with no obvious safe operating area protection.

Thank you, I added a pullup but the problem is still there.

Q1 is used because I need to drive about 8-10A. That transistor is rated to 15A, but U1 will only do 1.5A, and not very efficiently.

Your suggestion of adding a Q2 pull up doesn't really solve my problem. The current through J3 is still too large.

The signal source is an analog output from another circuit. The final intent is to hold the voltage around 13V regardless of what external load I put on the battery.