Any recommendations for 1A+ current source designs that have very good thermal stability? Something with local feedback, not for accuracy, but for thermal stability?
bump
to clarify, im looking for something that maybe tracks vbe of the current source device so vbe, I, and heat don't forever increase.
to clarify, im looking for something that maybe tracks vbe of the current source device so vbe, I, and heat don't forever increase.
headroom/dropout V, output compliance V range, output impednace vs frequency requirements are also useful for design in addition to actual Tempco/power stability requirement number
LM317 cascoded with IXYS depletion mode 6 A power MOSFET may meet some sets of requirements
LM317 cascoded with IXYS depletion mode 6 A power MOSFET may meet some sets of requirements
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I'm looking for a solution that only uses discrete devices.
Here is the scenario I'm trying to avoid for a circuit such what is attached (sorry for the crude drawing):
Constant bias being applied to the BJT, say 1V, and vbe at t=0 is 0.7, so the current is 0.3/R. And lets just say R is 0.3 for a 1A bias. I'm looking to avoid this:
BJT heats up > reduction of vbe > vbe/r current goes up > device heats up more > further reduction in vbe > etc
Then thermal runaway. Basically I'm looking for a circuit that has good tracking of the bias being applied to the BJT. I suppose I could mirror the current and thermal match, but that would add another power device. Looking to avoid that too.
Why not read these...
http://waltjung.org/PDFs/Sources_101_P1.pdf
http://waltjung.org/PDFs/Sources_101_P2.pdf
It would seem a trifle dogmatic to exclude a solution just because it uses an IC.
http://waltjung.org/PDFs/Sources_101_P1.pdf
http://waltjung.org/PDFs/Sources_101_P2.pdf
It would seem a trifle dogmatic to exclude a solution just because it uses an IC.
or 2 Q in "loop" feedback?
"ring of two" bjt feedback ccs uses the Vbe of the feedback/control Q - the heating of the pass Q only has an effect through h_fe tempco (or MOSFET Vth TC divided by loop gain)
pic below was just something I had on hand - hope you can parse pnp source version of the topologies
left most uses a higer Vref - 10 V Zener, and "Baxandal" or "complementary Darlington" - the Vbe nominally cancel - but you would have to bolt both to the same heatsink if large power were involved - and the tracking would have long thermal time constant
the other 2 are the "ring of two" - middle one cascoded
"ring of two" bjt feedback ccs uses the Vbe of the feedback/control Q - the heating of the pass Q only has an effect through h_fe tempco (or MOSFET Vth TC divided by loop gain)
pic below was just something I had on hand - hope you can parse pnp source version of the topologies
left most uses a higer Vref - 10 V Zener, and "Baxandal" or "complementary Darlington" - the Vbe nominally cancel - but you would have to bolt both to the same heatsink if large power were involved - and the tracking would have long thermal time constant
the other 2 are the "ring of two" - middle one cascoded
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