I am in need of a constant current source that can put out about 250 to 300mA and that can operate while dropping minimum volts across it -- on the order of 4 to 5V or less would be great. I am currently just using a LM317 with a RESISTOR which works, but I am sure something else will work better.
I'll use these in several places, but in particular I need to supply a 5V 250mA TUBE filament and I have 9.5VDC to work with. I'll also need it for a shunt regulator that feeds a circuit that needs 15V at ~150mA from a ~20V supply.
Any ideas?
I'll use these in several places, but in particular I need to supply a 5V 250mA TUBE filament and I have 9.5VDC to work with. I'll also need it for a shunt regulator that feeds a circuit that needs 15V at ~150mA from a ~20V supply.
Any ideas?
Depletion mode MOSFET. They are very simple to use - just short the gate to the source, like a JFET current source, optionally with a resistor to set the current. You will probably need to cascode it to keep the power dissipation down unless you can get a big enough one.
Salas said:
Thanks. R1 sets the current?
Besides the filament one, I'll use the others in an update to this project: http://www.diyaudio.com/forums/showthread.php?s=&threadid=141865
Mr Evil said:
I've used the 10m45's and the dn2540's, but I was looking for something a little better. Can you really get that much current from a cascode of these? I had assumed not, but maybe I'll try it.
dsavitsk said:
You are welcome. Yes, I=Roughly0.66/R1. Dissipation of CCS Mosfet = about Vin-Vout * I CCS. Dissipation of shunt Mosfet = (I CCS - Iload)*Vout. Arrange your sinking.
You can get ones that will give you plenty of current at low Vds, suitable for using a pair in cascode (IXYS do some), but the trouble is they don't have enough power handling. I don't know of any larger ones, but there may be some out there. You don't need to use one for the cascode though, you could use an ordinary low-threshold enhancement MOSFET with a zener or diode string to provide a bias voltage for it.dsavitsk said:
This would end up more expensive than Salas's solution, but possibly with better performance.
I thaught the Lm317t was fine for a current source? Why would
you need better for a filiment supply? But here is an idea use the
Lm317t as a ccs but use a R C network between the ccs and the
tube something like .2ohm and 100uf and .1uf film bypass.
you need better for a filiment supply? But here is an idea use the
Lm317t as a ccs but use a R C network between the ccs and the
tube something like .2ohm and 100uf and .1uf film bypass.
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