JFET Constant Current Sources
Hi Rudolf,
Jfet's make much poorer and less predictable current sources than bipolar transistors. To quote from Horowitz: "It is important to realize that a good bipolar transistor current source will give far better predictability and stability than a JFET current source" .
Hi Rudolf,
Jfet's make much poorer and less predictable current sources than bipolar transistors. To quote from Horowitz: "It is important to realize that a good bipolar transistor current source will give far better predictability and stability than a JFET current source" .
Stable current
They are fine for audio circuits and the value of current can be tuned by selecting the right source resistor. They can be simpler and made as a two terminal devices which is not easy for a BJT current source. Oh yeah.... they sound better. Keep in mind that Howowitz comes from an instrumention backgrund where precision is much more important than in most audio applications.
http://mc.harvard.edu/
They are fine for audio circuits and the value of current can be tuned by selecting the right source resistor. They can be simpler and made as a two terminal devices which is not easy for a BJT current source. Oh yeah.... they sound better. Keep in mind that Howowitz comes from an instrumention backgrund where precision is much more important than in most audio applications.
http://mc.harvard.edu/
Attachments
The idea is to feed LM431 shunt regulators for several supplies.
I've read that feeding them with a current source has some sonic benefit above just a series resistor (at least for analog supplies).
Another reason I want to use a 2 terminal CCS is, I sometimes use unregulated supplies; so using resistors they turn out big and the LM431 might be overloaded when coping with voltage
variations=>current variations.
For larger currents, say 50mA at Vds=10~15V one jfet can't handle all the power, so I want to parallel two jfets...
Any suggestions for types ? I think one needs jfets with low "goss". Are the J111/112 good candidates for idds 20 and up ?
Rudolf
I've read that feeding them with a current source has some sonic benefit above just a series resistor (at least for analog supplies).
Another reason I want to use a 2 terminal CCS is, I sometimes use unregulated supplies; so using resistors they turn out big and the LM431 might be overloaded when coping with voltage
variations=>current variations.
For larger currents, say 50mA at Vds=10~15V one jfet can't handle all the power, so I want to parallel two jfets...
Any suggestions for types ? I think one needs jfets with low "goss". Are the J111/112 good candidates for idds 20 and up ?
Rudolf
Rudolf
If you haven't already seen it, have a look at AN103 at:
http://www.vishay.com/brands/siliconix/SSFan.html
Geoff
If you haven't already seen it, have a look at AN103 at:
http://www.vishay.com/brands/siliconix/SSFan.html
Geoff
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