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: Hammy on 24 Jun 2010 16:35
On Thu, 24 Jun 2010 14:59:01 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >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. I was going to suggest the TL431. They are cheap and as common as dirt. The Electronics store by you probaly even stocks them. Look in the data sheet for CCS. Examples are there for sink or source. http://www.fairchildsemi.com/ds/TL%2FTL431.pdf Texas instruments TL431 Data sheet has lots of application examples for the tl431 its big though if your on dial-up. http://focus.ti.com/lit/ds/symlink/tl431a.pdf |