REVIEW - Lambda/EMI BOS/S bipolar operational PS or "40 pound OP AMP"

[alm]

So if I understand, a 4 quadrant bipolar supply can act as an Eload but it is different in that it is a current source and sink where it will pull current out of a supply if necessary to maintain the set current where a regular Eload is only a dynamic resistive load. 

Electronic loads can work in constant resistance, constant current or constant voltage mode. Not all loads may have all modes. The main difference between a four quadrant supply (no need to add bipolar, four quadrant already means any combination of neg/pos voltage and current) and electronic load is that an electronic load can't source current or voltage, only sink it. If you short a load, the current will be zero. If you short a four quadrant power supply, it will source the set (negative) current.

[robrenz]

Thanks Mecha and alm.

More tests in trying to understand how the Power Designs PS when in current limit can read less Amps than the in circuit Fluke. Please comment.

I take the total test leads and fluke ammeter loop that I am using to connect the PS to the BOSS and short the banana's that plug into the BOSS. I then dial in the compliance voltage necessary to drive 2.000 amps on the PS which is 184mV.  So that is the voltage drop of the leads + Fluke shunt. I leave that voltage setting on the PS.

Plug those banana's into the BOSS and dial -2.000A in CC mode.  Fluke reads 2.0A,  PS meter reads 2.0A.  Voltage reading at the PS terminals is 182mV and reading at BOSS terminals is 0.0mV.  No voltage is being supplied by the load and there is no excess voltage available from the PS because it is set to the exact voltage drop of the test/meter connection. So the BOSS in this state is acting as a close to zero ohm short.

Now turn the current limit of the PS down until it reads 1.5A on its meter.  Fluke and BOSS still read 2.000A,  Voltage reading at the PS terminals is -0.862V and reading at BOSS terminals is -1.039V  a difference of 177mV which is the leads/fluke voltage drop.  The PS has a diode between + and - output to shunt reverse voltage input which is letting the -.862V pass but the diode is dropping approximately 0.7V itself.  To test that I turn the power supply off and drive 100mA into it and the voltage drop across the PS output terminals is 0.700V.

Here is my take/guess after experimenting with 2 regular power supplies a diode and 3 ammeters. (It initially looked like I found a way to make current flow bidirectionally thru a diode  )
When the PS is supplying 2A in CV mode with only compliance voltage the BOSS is sinking 2A and supplies no voltage. The compliance voltage of the PS has the protection diode reverse biased.  2A is circulating thru the PS and BOSS.
Now set PS to 1.5A in Current limit mode.  PS ammeter reads 1.5A and BOSS and Fluke meter read 2A.   1.5A is now circulating thru the PS and BOSS. but an additional current loop of .5A is now circulating thru the protection diode and the BOSS.  The Fluke/BOSS meters are reading the sum of the two loops (1.5 +0.5) and the PS meter is reading the 1.5.  The BOSS has to now source the 0.5 amp instead of sinking so the voltage polarity flips to - 0.862V which is the voltage drop of the PS protection diode plus the 177mV needed for the voltage drop of the leads.

Is this correct?

[saturation]

Hi robrenz,

Yes, I think so.  I haven't commented as of yet as I needed the time to read your setup thoroughly, but in general, and depending on what your 4Q PSU is designed to do, the PSU could provide the balance of current that the DUT does not provide to insure the dialed in current remain constant.  However, you may be able to defeat it so you can sink purely from the DUT.  It can create a bit of a headache if you want to determine a DUT's real capabilities, without the PSU compensating.  For example to test a battery's AH, once the knee of the discharge curve occurs, which signals a rapid deterioration in output current, the PSU may begin charging the battery at that point, when you really want it to fail.  Also, an eload can be programmed to terminate the test and disconnect the DUT once a low-end cutoff voltage is reached, and you'll have to figure a way to configure a 4Q supply to do the same.

The Fluke/BOSS meters are reading the sum of the two loops (1.5 +0.5) and the PS meter is reading the 1.5.  The BOSS has to now source the 0.5 amp instead of sinking so the voltage polarity flips to - 0.862V which is the voltage drop of the PS protection diode plus the 177mV needed for the voltage drop of the leads.

Is this correct?