4mA current regulator
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From: krw on 24 Jun 2010 19:09 On Thu, 24 Jun 2010 09:38:24 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On Jun 24, 12:30�pm, panfilero <panfil...(a)gmail.com> wrote: >> can anyone offer any suggestions on how to make a simple 4mA current >> regulator... I started looking at LM317 voltage regulators, but found >> that they're gonna output a minimum of 10mA... I'm now looking at >> JFETs with a resistor between the source and gate... most the JFETs >> I'm finding can only provide currents less than 3mA... >> >> thanks > >You didn't give any specs. > >Here's a quickie, for lax needs: > >(view in Courier font) > > Vcc > -+- > | > .-. > | | R1 V > | | | | i.out > '-' | V > | | > | |/ > +-----| Q1 > | |>. > --- | > \ /~~> | > --- .-. >LED | | | R2 > | | | > | '-' > | | > === === Same idea but (a lot) better accuracy... | VCC | | | | | I(sink) .-. | V | | | | | | '-' |/ +-----+---------| | | |> | |/ | +---| | |> | | .-. | | | LM385 z | | -or- A '-' REF1112 | | | | === === GND GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
From: David Eather on 24 Jun 2010 21:45 On 25/06/2010 2:30 AM, panfilero wrote: > can anyone offer any suggestions on how to make a simple 4mA current > regulator... I started looking at LM317 voltage regulators, but found > that they're gonna output a minimum of 10mA... I'm now looking at > JFETs with a resistor between the source and gate... most the JFETs > I'm finding can only provide currents less than 3mA... > > thanks http://www.national.com/mpf/LM/LM334.html Simple, cheap, source or sink, very nice.
From: Jim Thompson on 24 Jun 2010 21:55 On Fri, 25 Jun 2010 11:45:40 +1000, David Eather <eather(a)tpg.com.au> wrote: >On 25/06/2010 2:30 AM, panfilero wrote: >> can anyone offer any suggestions on how to make a simple 4mA current >> regulator... I started looking at LM317 voltage regulators, but found >> that they're gonna output a minimum of 10mA... I'm now looking at >> JFETs with a resistor between the source and gate... most the JFETs >> I'm finding can only provide currents less than 3mA... >> >> thanks > > > >http://www.national.com/mpf/LM/LM334.html > >Simple, cheap, source or sink, very nice. Except with a TC... proportional to absolute �K... still usable in a lot of non-critical applications. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama: A reincarnation of Nixon, narcissistically posing in politically-correct black-face, but with fewer scruples.
From: Winfield Hill on 24 Jun 2010 22:01 panfilero wrote... > >> can anyone offer any suggestions on how to make a simple 4mA >> current regulator... I started looking at LM317 voltage regulators, >> but found that they're gonna output a minimum of 10mA... I'm now >> looking at JFETs with a resistor between the source and gate... >> most the JFETs I'm finding can only provide currents less than 3mA... and this, > Thanks for the responses... what I'm trying to do is power an > accelerometer.... I'm trying to re-create the "Constant Current > Signal Conditioner" side of the circuit shown in Fig. 7 of this link > http://www.pcb.com/techsupport/tech_signal.php but in that circuit > they use a "Current Regulating Diode". I don't have one of these, > but I do have an electronics store down the street, so basically > that's what I'm trying to re-create, and for the accelerometer I > have, the current would have to be regulated to 4mA... Yep, in the old days we relied on a LM317 for this task, even tho NSC's spec said the "minimum load current" was 5mA. Most parts were lower, 3.5mA typ, but it was clearly "out of spec" for 4mA uses such as yours. These days, distributors would do well stock Linear Technology's new LT3092 to serve the voracious current-source community. It has a 0.5mA minimum-load-current spec, and it has an intrinsic 1% accuracy spec (not counting resistor accuracy). For 0.5mA to 200mA current sources, this could be your baby. But, oops! if high currents are your requirement, it doesn't come in a TO-220 power case. For that, grab their LT3080ET, it's ready for a heat-sink clip! But it's possible it may need a parallel output capacitor to prevent RF oscillation. It has the same 0.5mA minimum-load-current, and 1% accuracy. dist: DigiKey case: TO-220 SOT-223 LT3092EST -- $3.73 LT3080ET $4.38 $4.20 -- Thanks, - Win
From: tm on 24 Jun 2010 22:15
"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:v1382618rb4qhf75pas3t870meblnr8aff(a)4ax.com... > On Fri, 25 Jun 2010 11:45:40 +1000, David Eather <eather(a)tpg.com.au> > wrote: > >>On 25/06/2010 2:30 AM, panfilero wrote: >>> can anyone offer any suggestions on how to make a simple 4mA current >>> regulator... I started looking at LM317 voltage regulators, but found >>> that they're gonna output a minimum of 10mA... I'm now looking at >>> JFETs with a resistor between the source and gate... most the JFETs >>> I'm finding can only provide currents less than 3mA... >>> >>> thanks >> >> >> >>http://www.national.com/mpf/LM/LM334.html >> >>Simple, cheap, source or sink, very nice. > > Except with a TC... proportional to absolute �K... still usable in a > lot of non-critical applications. > That can be tuned out with an additional diode and resistor. T |