I have used exactly the same circuit with good results. With -24 volts the IXYS chip works good. A slight improvement may be noted with much higher voltages.
If you have less voltage and only need 10mA, check out the National LM334. I have used that one with a - 7 volt supply (rectified 6.3 V). It is only good to 40 volts max, 10 mA max.
If you have less voltage and only need 10mA, check out the National LM334. I have used that one with a - 7 volt supply (rectified 6.3 V). It is only good to 40 volts max, 10 mA max.
Go to www.national.com and insert LM334 into the search box. The product page will show up. There are two circuits shown, you want the simple one on the right. Yeah, just a resistor and the chip. For 8 mA the resistor will be about 10 ohms. Connect the bottom terminal (V-) to your negative voltage source. and the top terminal (V+) to the 12AV7 cathodes. This chip will function with less than a volt so you may get by without a negative voltage (ground the V- terminal) although I have found that the chip likes some headroom. Rectified 6.3V is fine. Don't use over -35 volts.
Morgan Jones uses this chip in some of his designs and it is mentioned in the third edition but I am not at home now, so I don't know the page numbers.
http://www.national.com/mpf/LM/LM334.html
Morgan Jones uses this chip in some of his designs and it is mentioned in the third edition but I am not at home now, so I don't know the page numbers.
http://www.national.com/mpf/LM/LM334.html
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