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DC/DC Switching Power Supply with Post Linear Regulators – FAB1515 Rev.B Design – Part 2

FAB Modules
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On my last article, I said the ripple/noise was around 9-10mV.  Sorry, I was wrong.

Voltage ripple was even LOWER than that with the post linear regulators. I didn’t bandwidth-limited the scope.

So now, with the 20Mhz BW limited button on the scope engaged, ripple voltage is a very low 1.8mV


DC/DC Switching Power Supply with Post Linear Regulators – FAB1515 Rev.B Design

FAB Modules, FAB1000 Power Modules
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Posted by: admin

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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Simulating a Filter Circuit (Equalizer) using CircuitLab

Applications, Promotion, Tips
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Posted by: admin is a cool web-based “workbench” where you can create circuits and simulate it.  You can do DC analysis, Time Domain, Frequency Domain analysis. I think it’s a great learning tool to “experiment” with circuits and see what will happen.  No special software need to be installed, you can run it on your web browser. I’m using Chrome browser in this example.

For example, shown below is a simplified circuit of the mid-frequencies of an LC based equalizer.  To keep things simple, we’re using 10K resistors, 10K potentiometer (represented by R4/R5) and a 0.1uf, 100mH and 1K resistors for the RLC component of our filter circuit.


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Difference between “Single-Supply” and “Rail-to-Rail” Opamps

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An opamp usually doesn’t know where the “Ground” terminal, so one can normally operate an opamp from a dual power supply (i.e. also called split power supply, +/-V supply voltages) or from single-supply voltages.  As long as you don’t exceed the Maximum Ratings specified by the Opamp datasheet, you can operate opamps using either single or dual supplies.

When you browse manufacturer websites though, you often see some Opamps specified as “Single-supply” and some as “Rail-to-Rail” opamps… what do they mean by this?

Before we highlight the difference between a “single-supply” and a “rail-to-rail” opamp, let’s show how a “normal” opamp behaves.

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