HP Power supply Master/Slave mode?? anyone familiar?

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HP Power supply Master/Slave mode?? anyone familiar?

I have a pair of HP 6299A power supplies I want to connect in series in Master-Slave auto tracking mode. the manual states this can be done and shows how to do it but talks about a Resistor "RX" that needs to be added. but is not real clear on what the value of RX should be?

Anyone have any experience with this?
Assuming they use the same setups (a very big assumption) the manual for the 6114A series explains this system very very well for master/slave, serial, parallel, and tracking.

They are similar and the 6299A manual is very detailed but they leave some info out. For example

Attached is a photo from the 6299A manual that shows how to connect 2 units
in Auto-Series Master/Slave mode.

Where I am getting confused is that the manual states

"The value of Resistor (Rx) is dependent on the maximum voltage rating
of the "master" supply. The value of Rx is this voltage divided by the
voltage programming current of the slave supply (1/Kp where Kp is the
voltage programming coefficient). The voltage of the slave is determined by
its voltage control setting.

I am very confused by that statement. How do I determine the value of Rx???
How do I know the programming current of the slave supply?? And furthermore,
by reading the last part, it sounds as if the slave supply has its own
voltage control?? I want the slave supply to track the master supply voltage
so if I adjust the master voltage, the slave follows automatically to the
same voltage. Not independently. So I am quite confused..

I am wondering if I can just connect A6 of the slave supply to the
A6-A7-A8 connection of the master supply without a resistor?



  • HP 6299A Auto Series.jpg
    HP 6299A Auto Series.jpg
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There is a section about determining the proper programming resistor based on the supply current in an earlier section I think. When I get home, I can dig it out. It deals with measuring the current to choose the right resistor for programming IIRC, though it is a bit obtusely worded.

Edit: Now that I'm thinking more I might be confused as well. I'll need to sit down and look at the manuals when I get home.
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Thank you everyone! I managed to get it figured out. Someone on a HP test equipment forum Pointed me to a Link for the HP Power Supply Handbook that had a better description of how the Master-Slave Voltage sense input worked and that keyed me to finding the solution.

1st there is an error in the schematic in the manual as shown above! BOTH power supplies have the Positive output tied to ground. now when you connect the slave supply in series with the master supply, you have just shorted out the master supply! took me a while to figure that one out! In the manual they show a 3 supply connection where the slave supplies are not linked to ground.

The formula in the manual still makes no sense to me. 3.3K is what the calculated value comes out to be and that does not work. I did find a section in the HP DC Supply Handbook that had a better functional description of how the Voltage programming section works! It states that input A6 is trying to stay at zero volts and that the Rx resistor combined with the internal voltage control form a voltage divider. And that ratio is what determines the output voltage. So armed with that knowledge, I looked up the schematic and found that the internal 10 turn voltage control pot is listed at 40K ohms. so I wired up a 100K 10 turn pot as a rheostat and set it for 40K to start. Fired up both supplies and found that it worked! The master now controls the slave and I was able to vary the external 10 turn put to adjust the voltage of the slave supply in relation to the master. SO setting the slave supply’s internal voltage control put to the middle (5 turns) and adjusting the external pot so that both supplies are the same voltage. I come up with 20K ohms for Rx!!! This allows you to adjust the slave supply if you need up or down in relation to the master. But the master voltage control moves both up and down from 0 to the top of the supply range (130v No load) within 1 volt of each other over the whole range! That’s pretty darn good for how old these supplies are and how beat up the 2nd one is!
see my link above yours?
the formula gives 30.3K not 3.3K?

set both supplies to max Vo and use Rx = 30K @ 100V , you should be well within 1V tracking.
I don't typically use any ground connections for testing* esp. for multiple supplies. The dia. should work if you pull them off.
*The ground heaven is a O-scope probe connection, it needs to move around.
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