Your Questions
#4 Get two RNF14FTD23K2 and any random switch I guess. That will give you a 24v mode and a 12v mode. Don't run it off 24v in 12v mode.
Yea, I think so to. I was thinking about that during my nap. If a FET shorts nothing will save it anyway.Current limit
I would really like a current limit. I would like a latching shut down though, Like whats in a PC PSU. And even though it's not the greatest idea, we *COULD* have such things trip off of just one of sense resistor... can't we? It won't protect all the FET's, but if things are working, it should keep the OP from turning the current up too much by accident, that's all we really need.
Cheep slot style car fusses can work for global over current IMHO. And maybe get and use a spare op-amp for the shutdown? So we don't have to use 100 milliohms resistors (my math says LOTS of power dissipation with 100 milliohms)
Lets see what we can come up with. But we could just limit the maximum current with the adjustment.
Did I miss a post? I was puzzeled by your comment about 1 current sense resistor? Are there still 10 130 milliohm resistors?
You lost me there...can you explain what you mean, why I would need two of those resistors and a switch?
()blivion, I think it's me, not you, but I still don't quite get it...so with the new schematic are you saying that we need to have two of the resistors RNF14FTD23K2 and the switch will make it so when I am connecting to 24v I only use one of the resistors, then when I am connecting to 12v I flip the switch and I am now connecting both resistors and that is the only difference?
@jocanon: A separate supply for the op-amps, and the addition of the 12v-24v switch are slightly different and unrelated things. Even with a separate supply on JUST the op-amps, one can still over current a 24v DUT with the switch in the 12v mode. *HOWEVER*, using a separate supply for both the op-amps AND the control line (instead of the switch) should/could make it a constant current system, (draws the same amps regardless of the voltage), thus eliminating any need to modify the existing load control schema.....I think we are maybe on to something with this...
just to make sure I am understanding, you are saying we would need 2 power supplies in total (not 3 right?), one to power the DUT and another to power the control input to the op-amps and the op-amps themselves? I would think that the power supply to the op-amps could just be a simple ac-dc plug.
My vote would be no overcurrent detect. What do you guys think?
Attached is a schematic that uses an LM35 temperature sensor to shut off the load at 100C and turn it back on at about 75C.
Also shown is an op amp to scale the current up to 5 volts = 50 amps. If we add a little voltmeter we could put in a switch to look at current, voltage and temperature.
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