5 Volt Regulator Card

[bowen44]

What would be the significance of testing a 5 Volt Regulator Card by taking the difference of two current measurements. One measurement at 15V and the other at 14V.

The voltage regulator is used to drive LS32 and LS13 Line Drivers and Receivers.

http://img146.imageshack.us/my.php?image=tifpowersupplyxh0.jpg

Thanks

 

[itsmoked]

Your question does not actually compute...

by taking the difference of two current measurements.
One measurement at 15V and the other at 14V

2 current measurements?
at 2 different voltages?

Four variables?

Can you be more precise?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[VEBill]

What are the expected test results (pass and fail criteria)? I assume if you have the Test Procedure, that you probably also have the Test Data Sheet at hand.

Are they looking for the same input current under both Vin conditions? Or constant power so that when V goes up, I goes down?

It sounds like it might be a test spec to weed out design using linear regulators. In other words, a procurement qualification test vice production testing.

Maybe...

 

[IRstuff]

Assuming a constant load, it should tell you the ability of the regulator to ignore line variations. Ideally, the load current difference should be zero, since the regulated output voltage ought to be a constant.

TTFN

FAQ731-376

 

[bowen44]

Sorry I was trying to be brief. Here is more detail to the question:

The 5V regulator card is used in a Tempest Isolation Filter (TIF). The TIF is installed on the interface lines to prevent inadvertent transmission of classified data. It receives 5 and 15 VDC operating power from another unit a Waveform Converter.

For a checkout procedure in a Technical Order T.O. it calls out to test regulator card by using two power supplies.

Set PS1 to 14 VDC and PS2 to 5.1 VDC.
Measure current on PS1 14 VDC.
Turn Off PS1 & PS2 and adjust PS1 to 15 VDC.
Turn On PS1 & PS2.
Measure current on PS1 15 VDC.

Calculate the difference of current measured from I(15VDC) - I(14VDC).

The T.O. states it should be between 75 to 125mA, but it was changed from 0 to 60mA difference with no explanation.

We have tested 19 TIFs with a low reading of 52mA and a hight reading of 110mA.

The question is this test providing useful criteria to pass or fail the TIF?

I am thinking as long as the 5V regulator card is providing the 5V output it is good.

I don't understand the usefulness of this test.

Any comments are much appreciated.

 

[IRstuff]

Why are you not asking the designer of the board? It seems to be a rather speculative question to ask random strangers about the merits of test for a design that no one has ever seen.

So, my guess is that a higher current may indicate a malfunction or defective components on the board.

TTFN

FAQ731-376

 

[itsmoked]

IRstuff why don't you look at the design? <link in OP's first post!>

bowen44; That test as stated doesn't make much sense to me either.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

A schematic simply represents some implementation of a requirement. Not having the requirement, you don't really know what the design intent was, hence, you don't have the full design. What I see is what appears to a be a brute-force design, i.e., the circuit seems to be design to dump 1 amp, regardless of the load. That's why the shunt regulator uses the same transistor as in the 1-A source. Maybe that's the intent, but maybe it's just a brute-force solution.

Moreover, the schematic shows that R6 is selected during test, so what is the test criteria that allows you to select the value of R6? Without that rather trivial piece of data, you can't even tell what the trip point of the shunt regulator is set for. Is the load exactly a 1-A load? or a resistive load? These are all critical design parameters that determine how the designer intended the circuit to behave.

We can make semi-educated guesses, hence, it's a speculative question.

TTFN

FAQ731-376

 

[VEBill]

I didn't following the link until just now - sorry.

A keyword is Tempest. There is a requirement to maintain huge isolation from the red (secret data) side to the black (outside world) side. That's why the circuit is so unusual. The constant current section is designed to, well, maintain a constant current in spite of any data current fluctuations on the red side.

As to the test itself? Hmmmm... Even 60mA is a fair chunk of 1 amp, so I don't understand the purpose of that particular test step either. The isolation and other key performance characteristics could be measured more-or-less directly.