You're welcome to post a Tech-chat schematic of your brilliant idea. Anyone can shoot their mouth off with a vague description of "just do this" or "just do that", and when we get down to it, most of the time they don't know their butt from a hole in the ground. So let's see a schematic of your brilliant simplification the rest of us incompetents overlooked.
I used the same LM324 model and I don't see it, the whole thing is way overdamped with a 250-350us charge-up of the '3704 gate no matter what time constant used for local feedback compensation. I did solve the problem of abusive battery plug-in with high surge current into the circuit, and that is to simply turn the MOSFET backwards, it makes a heck of a good clamp diode, and circuit dynamics are essentially unchanged. This thing will be finished with some interlock stuff to prevent discharge on power loss and reverse battery protection: View in a fixed-width font such as Courier.
. . . . .-----+-----------+ .------------. . | | | | - ----------- . | +---[100k]--|---------. | | _ _ | . |+9V | / | | | | /| _| || .--- | *cutoff | [6.8K] | | - | | || . - .--+--. adj | | | | ' o - - | . | | | | /| | | ----------- . | | [2.7k] |/+|-[1K]-+----[50]-+-------+ | . | | | .--< | | | | . | --- | | |\-|----. | | | . | / \----+ | | \| | | | | . | --- | | | | | | IRF3704 | . | | | +-----||---+ | S| | . | | [2.7k] | | 15N | [0.3] -|| | . | | | | | | | '>||-+--. | . | | +----------[1K]--' | -|| | | | . | | | | | | D| | | | . | | [50] | | 44mV | | [1k] | | . | | | | | | | | | | . '--+-----+-----|--+-------------------+-------+----+--|----' . | | | | .--- | --- | .com | /// | . | | . | +9V | . | | | . | |/ | . | +-------| 2N2222 | . | | |> | . | | | | . '--[100]----+-[1k]----+----------------+ . | | | . | |< | to cutoff . +-------| 2N2907 | detect . |\ | . | | | . com | \ / . | . | . | . |
Actually if power supply abuse is a concern, leaving the MOSFET forward connected and reducing the gate current drive will give it milliseconds to respond to the connection and pull the current limit into regulation, but the MOSFET needs to be heatsinked for something like 20W: View in a fixed-width font such as Courier.
. . . . .-----+-----------+ .------------. . | | | | - ----------- . | +---[100k]--|---------. | | _ _ | . |+9V | / | | | | /| _| || .--- | *cutoff | [6.8K] | | - | | || . - .--+--. adj | | | | ' o - - | . | | | | /| | | ----------- . | | [2.7k] |/+|-[1K]-+----[50]-+-------+ | . | | | .--< | | | | . | --- | | |\-|----. | | | . | / \----+ | | \| | | | | . | --- | | | | | | IRF3704 | . | | | +-----||---+ | D| | . | | [2.7k] | | 15N | [0.3] -|| | . | | | | | | | >||-+--. | . | | +----------[1K]--' | '-|| | | | . | | | | | | S| | | | . | | [50] | | 44mV | | [1k] | | . | | | | | | | | | | . '--+-----+-----|--+-------------------+-------+----+--|----' . | | | | .--- | --- | .com | /// | . | | . '------------------[100]---------------+ . | to cutoff . | detect . | . | | . | \ /
Did you zoom in on where the waveform reaches closure? I saw some fine "oscillation"/slew-hunting.
Good idea, Fred!
[snip]...Jim Thompson
Hey, your ok Fred! :))
Implementation depends on regulator, input voltage, etc.
If the regulator is switching the current could be detected by looking at duty cycle, frequency, or whatever. That would be teh simplest solution.
For a linear regulator: bypass the pass device with a current regulator set to the desired end point. Note: current source should have a disable input.
In the linear regulator, detect when the error amp output hits its limit. It may well be that this ouput goes to 0 v or negative. Detect with comparator, spare opamp, discrete transistor with base resistor, or even tie to logic with a resistor.
This output going 0 or negative has to shut off both the linear regulator and the current source. Shutting off the current source and reducing the output set voltage of the power supply is enough: the supply will stay out of regulation as the setpoint is lower, but charging has stopped.
Do not make the voltage too low: the supply has to come back into regulation when an empty battery is connected.
The reduced voltage will keep the supply out of regulation, giving a schmitt trigger effect.
Kill the current source by pulling a node to ground. Change the reference or feedback, depending which way you feel, to reduce teh voltage of the main regulator.
TO do it quick and dirty, one needs:
Three diodes, two resistors and a transistor for a (poor) current source.
Tie its base to ground to shut it down: 2nd transistor. Mayeb a diode in the ouput for protection.
3rd transistor + resistor is the required inverter that drives this from the op-amp output. Use the collector of this transistor as the ground of the feedback divider if you feel like doing things the dirty way (changing the supply output voltage).You need some capacitance on the output (probably via a resistor) to keep everything from oscillating of no battery is connected.
I hope you enjoy your schematic drawing program, I'm looking forward to the picture.
Thomas
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