4mA current regulator
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From: Tim Wescott on 24 Jun 2010 14:28 On 06/24/2010 10:57 AM, panfilero wrote: > 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... Use a PNP current mirror. Or, if you shy away in fear from transistors, a "howlin'" Howland current source will provide you with man-days of entertainment trying to get it to stay stable under all conditions. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Spehro Pefhany on 24 Jun 2010 14:59 On Thu, 24 Jun 2010 10:57:20 -0700 (PDT), panfilero <panfilero(a)gmail.com> wrote: >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 If you want to follow the example circuit, you could use a 1N5313 for a couple of dollars from Mouser. You could also create this with something like a TL431 reference, an op-amp, a PNP transistor or small p-channel MOSFET and a few passives and get higher output impedance at low frequencies.
From: John Larkin on 24 Jun 2010 14:57 On Thu, 24 Jun 2010 10:56:14 -0700 (PDT), panfilero <panfilero(a)gmail.com> wrote: >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. 4 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 If the system is AC coupled and the calibration isn't critical, you could start with just a resistor to a DC voltage. +20 and 2.5K, or +30 and 5K maybe. John
From: George Herold on 24 Jun 2010 16:34 On Jun 24, 1:57 pm, panfilero <panfil...(a)gmail.com> wrote: > 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 Though not nearly as cheap as a transistor you can use a voltage reference an opamp and resistor. Vin---* Ref *Vref---+ * | 'GND' / | R | / +-+-----> I out = Vref/R +----< | | \ --+ | \ | | +----------+ George H.
From: Tim Williams on 24 Jun 2010 17:04
Take your pick: http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Current_Sinks.png These are in any textbook. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "panfilero" <panfilero(a)gmail.com> wrote in message news:1f931fa4-0974-4f2e-9a4e-f166a28ba8be(a)w31g2000yqb.googlegroups.com... > 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 |