Low Current Power Supply

[samchieh]

Hi Everyone,

Does anyone know of a power supply that's capable of +-5V but with

the ability to sense the current being supplied at the 100uA level?

Thanks!

Sam

 

[kspalla]

question is not clear, do u want battery or sensor?

 

[karesz]

hi,
I think samchieh need a+/- 5V supply with current measuring in hight of 100uAmpers...
@samchieh
Maybe you will us more tell pls from the (top?) secret details?
K.

 

[samchieh]

Well....I want to measure the amount of gate current being drawn from a power amplifier i'm measuring. The current is on the order of 100uA, I'm not sure if there is a piece of equipment out there that can actually do this.....

thanks!

 

[karesz]

Hi,
I think too, but you can build it surly self too...
I would take the smallst +/_ power regulators (maybe 7805/7905L (Transistor package-or SMD if it exists) & measure the drop voltages over i.e. both 1K Ohms, then Instr Amps & finisched ...
I had so 14 years ago a project for current measurements from a semiconductor detector supplyed upto +150V/1ma & 0.1mA.
I realized it with "Switced Capacitor Sampler", an IC from Linear Techn, but I must search for that in my documents/logbook-if you need idea...
Greetings!
K.

 

[samchieh]

Thanks! That was my first thought too, just make one. Thanks again!

 

[karesz]

So, I found the old sketch, but it was realized with (pro Channel)2xM6225, Coto Wabash, OptoMOS copplers & pro current/voltage 2x good 1uF foil capacitors(switched charge memory) and OP07 for monitored voltages & a chopper amp_LTC1150_for 200uA/2mA current measuring.
Sensitivity switcher was per telecommand from a computer through a relay controlled...
The Detector current are sampled over a serial 1KOhm , filtered in both lines with two serial 10KOhms. & on the schema can you see the 100nF input capacitors to that filterings...
Through these switched capacitor sampling technique-you are polarity independent, you must only change the two input wires.
Todays opamps are really better, as the chopper amp so 20 years ago, but its function was not bad. The 6 channel meters are realized as a two sided PCB plug-in module. from 1mA it delivered 10V & from 100uA even 1V, has not the same output values on identical channels; depending from component tolerances, but with, for longtime, stabile deviances pro channel.
K.
Maxim & I think Burr Brown has good "Up-Side" current meter solutions, in remember all case for positive supply, but can not more tell whats the lowest measured current ...

 

[kender]

Well....I want to measure the amount of gate current being drawn from a power amplifier i'm measuring. The current is on the order of 100uA...

What range of currents do you expect? Is 100uA a standby current or max current? Could you tell a little more about your power amplifier, which consumes only 100uA @ +/-5V?

 

[karesz]

Hi Kender,
I think "the specs" are enough clear: from low pwr +/-5V suppl are the currents up to max 1mA to measure...
Othe question is the joke of 78/79L regulators with hes high self or GND currents, often over ~3 mA :-(
I know over moderner regulators (Linear Tech/NI & Micrel...) they need/has so at 100 uA or less, but I remember only for positive regulators.
I applyed some years ago +/- CMOS regulators (under 3V outputs and in high (sold only in high volumen) from Torex, they are very good, but nothing for these project :-(
I would build it nowadays with a double OpAmp as a real "+/- 5V reference voltage source"(see applications circuits from ADR435 i.e.) , with so 1 K Ohms in serie for the current sensing/measurings through newer Instr. Amps.
K....

 

[karesz]

Hali,
I found yet a very fine high-side current meter chip from Maxim, but its only for positive supply & unidirectional_ otherside is very small in SOT23-5 & needs only 1uA!, has an offset of max ~0.3mV...
So can measure i.e. over a 100 Ohm your uAmps too!
K.

 

[samchieh]

Thanks all! This was very helpful!!!

 

[karesz]

Hali,
These isnt exact for your application, but I did read even over that; their are nice Isolated Current Sensors (sampled at 75/150 & 300KHz) from +/-20A up to +/-500A, with Resolutions 1--10mA....
K.