Hello everyone,
I'm putting together a headphone amplifier that calls for a constant current diode (AKA current regulator diode). These are essentially impossible to find where I live, so I need to find an alternative. The diode in question supplies 4.7mA from a 32V supply, feeding the base of a BD139 transistor.
I've done a lot of reading both here on DIYAudio and elsewhere. I've looked at LM317, LMx34 and other circuits - analysis paralysis has kicked in and my head is beginning to spin
.
Could someone help point me in the right direction?
I'm putting together a headphone amplifier that calls for a constant current diode (AKA current regulator diode). These are essentially impossible to find where I live, so I need to find an alternative. The diode in question supplies 4.7mA from a 32V supply, feeding the base of a BD139 transistor.
I've done a lot of reading both here on DIYAudio and elsewhere. I've looked at LM317, LMx34 and other circuits - analysis paralysis has kicked in and my head is beginning to spin
. Could someone help point me in the right direction?
A constant current diode is a JFET. http://www.vishay.com/docs/70596/70596.pdf
BTW, where is it that you live where you can't buy them?
BTW, where is it that you live where you can't buy them?
Like this. The JFET and resistor equate to a two terminal device like your CC diode.
The resistor has to be selected on test to suit the FET. Notice how the current is constant in relation to the rising supply.
Edit... you need to be sure you have sufficient voltage headroom for the FET to work. If you post the headphone circuit we might be able to suggest another alternative such as a bjt transistor CCS.
The resistor has to be selected on test to suit the FET. Notice how the current is constant in relation to the rising supply.
Edit... you need to be sure you have sufficient voltage headroom for the FET to work. If you post the headphone circuit we might be able to suggest another alternative such as a bjt transistor CCS.
Attachments
A few more ideas here: Improved 2W current sources (II) and in the previous thread mentioned in the first post
What Mooly said. And you can use a cheapo ($.40) J112 instead of the dear ($.86) 2N3819. Use a pot instead of the fixed resistor and dial in the desired current. The constant current diode probably has some temperature correction going on. There are ways to do this with discrete parts. How critical is your mission?
Last edited:
C'mon, in building many designs shown here, not to say the most of them, we'll bury several k$ or k€. So what?
Best regards!
It really is impossible to help someone who cannot afford to spend $1.
A really cheap solution that is used in really crap designs is to just use a resistor.
A really cheap solution that is used in really crap designs is to just use a resistor.
The solution all depends on what components you can buy within your meagre budget.
The BJT with a diode and a few resistors will build a reasonable CCS.
It's pretty easy to design, Rset is chosen so that Vbe - Vdiode is dropped at the required current
An LED is shown as they are low noise. If Vled is 2.1V and Vbe is 0.66V then Rset = 1.46V/Iout . So for Iout = 10mA you could use 150R
The BJT with a diode and a few resistors will build a reasonable CCS.
It's pretty easy to design, Rset is chosen so that Vbe - Vdiode is dropped at the required current
An LED is shown as they are low noise. If Vled is 2.1V and Vbe is 0.66V then Rset = 1.46V/Iout . So for Iout = 10mA you could use 150R
Attachments
Last edited:
None of the LM334 and similar ideas work here, I wonder why you suggest them .
The OP does not need a constant current to a grounded load supply, but two terminal current source, a very different thing.
The FET or bipolar based suggestions are fine, of course.
The OP does not need a constant current to a grounded load supply, but two terminal current source, a very different thing.
The FET or bipolar based suggestions are fine, of course.
- Status
- Not open for further replies.