4mA current regulator
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From: Jim Thompson on 24 Jun 2010 17:59 On Thu, 24 Jun 2010 09:30:22 -0700 (PDT), panfilero <panfilero(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 Surf on "Larkin Magic Diode" :-) ...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: Dave Platt on 24 Jun 2010 18:25 >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... The old 2N3819 seems to have a very wide range of Idss values (not unusual for JFETs). The version from Temic, for example, lists Idss as being "min 2, typical 10, max 20", with cutoff voltages of -3 typical and -8 maximum. If you don't mind buying a few and hand-selecting you can probably locate one which will fit your circuit. They're all of $.09 each from Jameco (quantity 10). If you want something a bit more modern for some strange reason: Fairchild has a whole bunch of JFETs with minimum Idss well above 4 mA: J110, J309, J310, PN5434, lots more, in several different package types. Mouser carries numerous types, mostly under $0.20 in single quantity (a few are more but not by all that much). Heck, I think I have a bag of 100 2N3819s I bought a few years ago when they were on-sale at Jameco for under a nickel each (overstock sale, I assume). If you're in the U.S., send me an email with your mailing address, and if I can find the bag I'll stick a few in an envelope and mail 'em to you to dig through. -- Dave Platt <dplatt(a)radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads!
From: John Larkin on 24 Jun 2010 19:02 On Thu, 24 Jun 2010 15:25:59 -0700, dplatt(a)radagast.org (Dave Platt) 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... > >The old 2N3819 seems to have a very wide range of Idss values (not >unusual for JFETs). The version from Temic, for example, lists Idss >as being "min 2, typical 10, max 20", with cutoff voltages of -3 >typical and -8 maximum. > >If you don't mind buying a few and hand-selecting you can probably >locate one which will fit your circuit. They're all of $.09 each from >Jameco (quantity 10). > >If you want something a bit more modern for some strange reason: >Fairchild has a whole bunch of JFETs with minimum Idss well above 4 >mA: J110, J309, J310, PN5434, lots more, in several different package >types. Mouser carries numerous types, mostly under $0.20 in single >quantity (a few are more but not by all that much). > >Heck, I think I have a bag of 100 2N3819s I bought a few years ago >when they were on-sale at Jameco for under a nickel each (overstock >sale, I assume). If you're in the U.S., send me an email with your >mailing address, and if I can find the bag I'll stick a few in an >envelope and mail 'em to you to dig through. If Idss is over 4 mA, you can stick a selected resistor or a pot in the source and tune the drain current. TC will be mediocre, but that may not matter to the OP. John
From: Barry on 24 Jun 2010 19:03 "panfilero" <panfilero(a)gmail.com> wrote in message news:da1d7dbc-f52d-4027-86a9-2c653c515d08(a)k39g2000yqb.googlegroups.com... > 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... > > thanks A constant current diode is just a JFET with the gate tied directly to the source. If you have a good collection of JFET's, you can likely find one where the I(sub)DSS is 4 mA. There is usually quite a spread in this current so picking a particular JFET should be done based on this spread. For example, the I(sub)DSS of a 2N4416 is typically between 5 and 15 mA. Some common JFET's and their corresponding I(sub)DSS ranges are shown in the table below. Having used many PCB Piezotronics parts before, I can suggest that you buy their charge amplifier if you need the ultimate in performance. If you can wait a while for mail order, Mouser stocks the 1N5311 diode which is spec'ed to be within the range of 3.24 to 3.96 mA. Dr. Barry L. Ornitz wa4vzq(a)live.com JFET Manufacturer I(sub)DSS Minimum I(sub)DSS Maximum MPF-102 On Semi 2N4416 Vishay 5 mA 15 mA 2N3819 Vishay 2 mA 20 mA MPF-102(obs.) Motorola 2 mA 20 mA 2N5457 Fairchild 1 mA 5 mA 2N5458 Fairchild 2 mA 9 mA 2N5459 Fairchild 4 mA 16 mA PN4303 Fairchild 4 mA 10 mA BFR30 NXP (Philips) 4 mA 10 mA BFR31 NXP 1 mA 5 mA 2SK722E Sanyo 2.5 mA 6 mA MPF-102 Fairchild 2 mA 20 mA 2N5557 Central 2 mA 5 mA Note: P-channel or N-channel determines the "direction" of the constant current diode.
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) |