I got my prototype boards for my FAB1515 (Rev.A) Power Supply Module. I built a prototype so I can finally evaluate and test it.  I know the V+ section and V- section works independently on the breadboard. But this PCB design combines the V+ and V- section (and also adds a 48V section) and I’m not sure how all of these DC/DC converters will interact with one another (since they will be all powered from the same 12V DC source).

After building the prototype, I hooked it up to my DIY Electronic Load, oscilloscope, and (2) bench meters. One of the bench meter monitors the Voltage output, and the other one monitors the current load.  The oscilloscope monitors the DC output and ripple, and the Electronic Load allows me to vary the current draw from a few milliamps to hundreds of milliamps.

Right away, I noticed some problem… the V+ section voltage reading was jumping all over (15.1xx to 15.2xx and higher ) and wouldn’t show a steady number on my voltmeter.  Based on experience, I know the cause of this is a too high ripple voltage.  Looking at the oscilloscope confirmed my fears… the ripple voltage was very high… too high… approaching 500mV. This is CRAP! The V- section was also exhibiting high ripple voltage, though not as high as the V+ section… but still, it was high, around 300mV.

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The DC/DC Converter part I’m planning to use with my FAB1215 module is out of stock, and even if it comes back in stock, the supply quantity is so low… Mouser doesn’t keep a big inventory of this part because they said demand is low. Soooo, I can’t depend on this part being available for my customers, so I decided to roll my own DC/DC converter for +/-15V output.

Making the 12VDC to +15V output was easy, and initial breadboard testing showed it can deliver up to 370mA and more (up to 500mA). But making the 12V to -15V Inverter was a bit more problematic. The best I can squeeze out of it is -150mA, and only at 58% efficiency.  The good news is I think that should be enough for 1 or 2 channels for a V- rail.  The V+ rail will need to power additional LEDs and Relays so I want the V+ to have a higher current rating anyway. So I think we’re good.

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We now sell a 6″ long Female-to-Female Ribbon Cable for use with FABModules. Click here to BUY a ready-made cable.

This 10-pin ribbon cable is required to connect the Power Supply FAB1215 to your FAB Module setup. If you’re using a FAB-to-Cable crossover adapter (FAB9001), you’ll also need this cable.

Step 1:  Cut your cable 7.5″ long.  Position cable as shown below, then crimp the connector. You can use an adjustable jaw pliers. I suggest wrapping the plastic connectors with cloth/rag to protect it before using the pliers.

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I decided to test how my FAB1248 DC/DC Converter will behave in a short circuit condition. It is unavaoidable to experience short circuit when you’re playing around with electronics. Sooner or later, you’ll experience it. The question is will the FAB Modules survive if there was ever an accidental short-circuit?

Will our FAB1248 Module release the magic smoke?  Will you need to buy another FAB Module from me to replace your short-circuited DC/DC Converter?

Here are the results of my testing:

TEST PROCEDURE:
We connected our FAB1215 Power Supply Module, with a FAB1248 plugin to a 12Volts DC Adapter (wall wart). We then attached a multimeter to monitor the voltage lines across GND and +48V output.

Voltage level (without load, open circuit) = 47.88Volts

Next, we connected the 48Volt line directly to Ground, thus creating a short-circuit condition. A big spark occurred. We let the 48Volt line connect to Ground for several seconds. Measured output voltage during this short circuit condition is 34.8mV according to the multimeter.

Next, we removed the short-circuit condition.  Measured output voltage went up to 1.25Volts, but not our original 47.8Volts…. Hmmmm….. at this point, I’m wondering if the FAB1248 survived… It doesn’t seem to be looking good. It’s only hovering around 1.25Volts.

Removed the 12Volts input voltage  from the FAB Module. Now, the measured output voltage is now 0 volts, naturally… since there is no voltage  input source.

Hooked up the 12Volts input again to the FAB Module…. Voila!  We measure 47.88Volts again, and our FAB1248 module is still working properly. I repeated this test procedure several times and each time, the FAB1248 comes back to life after doing a “reset” …. just unplug the 12Volt source, and plug it again.

So I’m happy to report, that yes, the FAB1248 will survive a short-circuit condition and not break down.  You may need to “reset” the converter by powering off, then powering back on…. of course, after you’ve removed the short-circuit condition.

I made some tests using the final component values for our FAB1248 DC/DC converter.

Using a 12Volts DC input, phantom power voltage output remained constant at 47.90Volts, up to 47.84Volts at various loads and current draw.

For example, at 57mA current load, voltage output measured is 47.87Volts, with 152mV ripple according to our oscilloscope. This translates to about 0.31% ripple!  Ripple frequency has a period of 6.07us, or 164.7khz.

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