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Author Topic: Power Supply for Z3801A GPSDO Frequency Standard  (Read 13543 times)

Posts: 618

« on: December 02, 2012, 11:58:41 PM »

As the subject line says, I'm trying to get my Z3801A up and running after it having been sitting around for several years.  I need to build a power supply for it.  It requires -54 volts (nominal) at about 750ma running, with a bit more during warmup to power dual crystal ovens (one inside the other) for the OCXO.  Most information I've read suggests just using an unregulated linear power supply but I am not comfortable with the power fluctuations when those ovens both come on at the same time.  Figured I'd use a simple basic regulator circuit like an LM337 or similar but found that the max. input voltage for the 337 is about 30 volts.  They do make a high(er) voltage version of the LM317 positive regulator but, apparently not the LM337 negative one.  If all else fails, I will use the LM317HVT, keeping both leads floating but I'd much rather use a negative regulator and tie the positive leads to common as they should be.  I don't want to use an off-the-shelf switching supply due to the potential for noise around my bench area.
I spent several hours last night looking through several vendors websites, looking for a suitable negative regulator with no success.  Any suggestions on a part number that is currently available?  All ideas welcome.  Thanks,

Posts: 933

« Reply #1 on: December 03, 2012, 12:56:30 AM »

An interesting challenge but easily solvable:

Use a suitably beefy PNP power transistor and if you can't find a 54V zener then chain lower voltages together till you get what you need. Don't forget suitable decoupling capacitors on the input and output


Posts: 1460


« Reply #2 on: December 03, 2012, 05:17:18 AM »

If that link doesn't work Jameco has 48v supplies and the 3.2A is $33.95


Posts: 5688

« Reply #3 on: December 03, 2012, 11:35:04 AM »

Don't sell the "Brute Force" regulation of the unregulated but well-filtered supply short.  

Large capacitance electrolytic(s) across the rectified output, supplied by AC transformer that has a bit of "stout" to its Current abilities, like maybe 1 or 2 Amps available, you've got it made.  

The heaters won't care and neither will the other circuitry, apparently, since most of the information you've read states that unregulated supplies do indeed work here.  

That said, if you insist, floating the standard three-terminal regs such that they are able to regulate their own voltage level above that of the supply works rather well, actually, as long as you first ascertain that whatever voltage drop your powered circuit demands won't either draw the AC supply down below the two volts or so above three-terminal output voltage and won't draw more current than the rating of the three-terminal reg, forcing it to go into thermal shutdown or the likes, but YOU DON'T NEED TO GO THROUGH ALL THAT if what the others told you about use of unregulated supply is good info.  Use of a Zener for the float rather than a resistor works well with the added margin of specificity of voltage over wider temperature ranges, but is not mandatory in a circuit that already has been run successfully with unregulated supply. 

Regulating the supply to xtal heaters won't really give you anything to gain, as those heaters don't really work fast enough to make this an issue.  Energy, given amount of mass, given resistance, there ya go.  Many don't even include thermostats in this kind of setup, relying on that simple physics calculation. 

« Last Edit: December 03, 2012, 11:39:02 AM by KE3WD » Logged

Posts: 144

« Reply #4 on: December 04, 2012, 06:23:25 PM »

I used one of the Jameco supplies Clif mentioned for a number of years running my two Z3801A boxes but I was always uncomfortable with having the open frame style supply running without any fusing.  I got a nice Tenma variable supply from MCM Electronics that will supply up to 60VDC at a max 1.6A (#72-8240) and has a nice display, current limiting capability, etc. and use it for a dedicated supply.  Unlike the old Jameco I can always see the 48VDC setting displayed along with the current being drawn (usually about 430mA when the Z-box is sitting "idle").  Yep, pricier than the open frame supply but I feel much more comfortable with it (priceless!).

73 - Dino KL0S

Posts: 2088

« Reply #5 on: December 05, 2012, 09:31:02 AM »

any telephone company power supply (they're called rectifiers in the trade) has an output in the 53-54 volt range.  they're made as small as one amp, and as large as hundreds of amps.  the ones I've used desktop at work have good regulation (they are paralleled in practice) and good ripple.  the big guns, being filtered by zillions of amps of battery filtering, may not be as clean.  but you won't be using one of those.

telco "central office battery" is based on positive-ground 48 volt lead-acid battery stacks, so the power supplies have to run a little hotter to charge the batteries.

yes, I said positive ground.  in the CO, red is negative voltage, and ground is "backwards."  you will need to keep that highly in mind if you use telco rectifiers.  your Fluke is your friend, watch it carefully Wink
« Last Edit: December 05, 2012, 09:34:22 AM by KD0REQ » Logged

Posts: 618

« Reply #6 on: December 06, 2012, 12:14:09 AM »

telco "central office battery" is based on positive-ground 48 volt lead-acid battery stacks, so the power supplies have to run a little hotter to charge the batteries.
yes, I said positive ground.  in the CO, red is negative voltage, and ground is "backwards."  you will need to keep that highly in mind if you use telco rectifiers.  your Fluke is your friend, watch it carefully Wink

Interesting you should mention that.  That's precisely why I need this configuration.  The Z3801 was built by Hewlett-Packard to telephone company specs. for the cellular networks, thus the need for the odd (at least to me) voltage and polarity.

Thanks to everyone for the suggestions; lots of viable solutions.  Being the miserly type and having more time than money, I think I'm going to go with Tanakasan's regulator.  Cheap and more than adequate for this application.  Seems I started with a three-terminal regulator in my mind and I just couldn't see past that to what I really needed.  It's easy to do, though.  Done it many times when troubleshooting a problem.  You start with one idea and just can't get it out of your head.

Thanks again to all who replied.
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