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Looking for a 10mA constant current source.

The LM185, unlike the LM185-xx parts, is a 3-terminal, adjustable voltage device. The LM185-xx parts are fixed-voltage,

2-terminal versions of the same part. For your temperature range, the LM385 commercial version suffices.

One might consider increasing Fred's feel-good resistor to take more of the 28V supply dissipation--120R only drops 1.2V.

Lastly, have you measured your noise diode's output power vs. drive current? You might only need the resistor, and that would be simpler now, wouldn't it?

Cheers, James

Reply to
dagmargoodboat
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I'd be inclined to investigate the LM317 family. Your temp range isn't going to challenge a modest tempco. 10mA is a doddle for even the 317LZ (TO-92) although to limit self-heating I'd contemplate the TO-220 pack.

Reply to
budgie

It's a feel good:

1) off-loads some power dissipation from the xstrs; 2) additional limit against turn-on transients (28V is switched); 3) HF isolation of regulator reactance from ND RF ckt.
Reply to
Fred Bloggs

Cheers.

--
Tony Williams.
Reply to
Tony Williams

Right-

Good- make that 1.2k

HP has a detector in there somewhere- the 5.6KHz is used to chop/amplify a noise sample and apply feedback to the DC supply.

Reply to
Fred Bloggs

The datasheet shows you how to achieve higher current: View in a fixed-width font such as Courier.

Vin | | e |/ +-------| | |\\ (+)| c +---+ | | L | | | M | | | 3 |R------+ | 3 | | | 4 | | +---+ [Rset] (-)| | | | +---------+ | | v

Vref ---- Rset

The drawback is there is no temperature compensation of the Vref

+214uV/oC in this circuit. But since the '334 servo's the transistor in order to maintain Vref across the R-(-) terminals, the diode temperature compensation technique still applies: View in a fixed-width font such as Courier.

Vin | | e |/ +------------| PN4250A | |\\ | c | | +-[1.5K]---||--+ | 0.1u | | | (+)| | +---+ | | L | | | M | | | 3 |R-+---------+ | 3 | | | | 4 | | | +---+ [14] [143] (-)| | | 14 and 143R | | | | | | 1% metal film | | | | | | +----+--|>|----+ 1N457A | | Vref Vref + VD | ---- + --------- ~ 10mA | R1 R2 | | | [1.2K] | | | - ^ ND | | gnd

Reply to
Fred Bloggs

I have an 8.67ma current source right here in my hot little hand. You can have it if you want it. E-mail me.

Norm Strong

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Reply to
<normanstrong

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