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Class D Switching Power Amplifiers and Power D/A conversion

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Old 20th August 2015, 07:52 PM   #391
twest820 is offline twest820
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U103: @Snake: Mouser has upwards of 86,000 TL074s in stock?
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Old 21st August 2015, 07:27 PM   #392
royalbee is offline royalbee  Israel
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boards arrived, thank you
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Old 22nd August 2015, 06:40 PM   #393
JLesterP is offline JLesterP  Philippines
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Originally Posted by ChocoHolic View Post
Hi Lester,
I do not have any special test rig, I am just using ordinary high power resistors and combine them in order to get the required resistance and power rating.
I.e. mounted below my workbench there are two resistor triples as shown in the attached picture. Each of this triples results in 4R capable of roughly 200W with some forced ventilation. With this 2x 4R I can get easily 2R, 4R, 8R - simply by series or parallel connection. If I need other values, I have to settle specific other resistor combinations...

Besides the resistor picture, I am also attaching a schematic showing the connection circuitry.
The down side of this method is that you need an extremely strong PSU already for moderate amps.
Consider the LiteAmp tested at 20A. Drawing this from 40V. The PSU and the resistor are stressed with 800W.
For larger amps usually you sinply do not have sufficient PSU and resistors to test this way.
But there is a simple trick for reducing the involved power, but stressing the amp with high currents.
Instead of giving zero input signal, you can jumper the input coupling cap(s) and feed a small DC voltage to the amp input.
I.e. if you have +/-40V rail, you can give a little DC input voltage bringing the output of the amp to +30V. Difference vs +40V is now just 10V (if rail does not sag). When now putting 0.5R between output and rail you will stress the amp 20A, but the PSU is not much loaded (200W only), because the switch mode amp will feed back a lot of current to the rail.
Always start with moderate currents, at high currents this measurement is really tough for the amp!
Duration of this test is short. Just some seconds, which you need to get the reading. When you stress the amp close to the shut down limit and use ASICs like the modern IRS types, which measure the drop across the Rdson, then you will observe a temperature effect.
Within few seconds the Rdson grows, which will then trigger the shut down.
If you do not have a reliable shut down, keep good margin vs max current with this measurement.

Interesting wave shapes:
If you are only interested in the switching behavior and taming HF resonances of the half bridge, then it is sufficient to measure the Vgs and Vds of the low side MosFet.
These two signals tell you 99% of the story.

If you also want to see the dead time under load conditons, you will have to measure the Vgs of the upper MosFet as well.
This either calls for a differential probe and a scope with deskew for the timedelay of the differential probe or a 4 chanel scope with large overdrive headroom and chanel substraction (Vg of upper Mos Fet vs neg rail minus Vds of lower MosFet).

Correct probe connections (do not use their long GND clips, but direct GND connection from the tip) and correct adjustment of the probes are essential for all these measurements.
Thank you for sharing info and answering my question even though I am not building your amp, really helpful for class-d starters. Schematic is helpful in getting the test correctly. Without it my amp might go boom.
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Old 23rd August 2015, 10:03 PM   #394
royalbee is offline royalbee  Israel
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can someone please advise on a suitable C110 (gain board) at mouser? the lowest leakage current i could find was 2uA?

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Old 24th August 2015, 06:24 PM   #395
ChocoHolic is offline ChocoHolic  Germany
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2uA is already at the lower end which manufacturers will guarantee.
The leakage is strongly depending on temperature and operating voltage.
I had chosen a 100V / 105C / 5uA type and selected manually for low leakage.
Counted Ok everything below 30nA at 5V and 25C.
Also tested some of them at 85C ad found them around 100...150nA.

Another option is to use ceramic SMD types of size 0805.
This size fits for manual soldering to the through hole pads of C110.
The advantage is that you do not need to select for low leakage.
Ceramics X7R have much lower leakage.
C2012X7R1C475K125AE TDK | Mouser
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Old 31st August 2015, 07:52 PM   #396
Cresnet is offline Cresnet  Jordan
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Originally Posted by Reactance View Post
Hi Marcus

Thought you deserved to see how my build was progressing.
I really wonder if C23 , C24, C25 , C26 in your board are 250VDC.
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Old 1st September 2015, 06:47 PM   #397
ChocoHolic is offline ChocoHolic  Germany
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..they look like:

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Old 3rd September 2015, 01:31 PM   #398
chienmort is offline chienmort
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Can I use SB1100 in place of MBR1100?
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Old 3rd September 2015, 07:42 PM   #399
ChocoHolic is offline ChocoHolic  Germany
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SB1100 has a slightly higher capacitance, nevertheless from theory it should easily work without trouble.
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Old 26th September 2015, 12:39 PM   #400
ChocoHolic is offline ChocoHolic  Germany
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Default LiteAmp Family

Here the LiteAmp family. All versions are fitting to the same PCB.
Furtheron it is time to fully publish also the Gerber Data.
For the higher voltages a detailed analysis of the switching stress and the capabilities of the IRFI4020 showed that already at 2x75V a 4R load would be too much of stretch for my taste.
My examinations showed that 2x70V and 8R with one IRFI4020 is more or less the limit for a reasonable design, which is similar to the choice of IR in their reference designs.
The LiteAmp has two IRFI devices in parallel, it has to be taken into account that load sharing will not allways be half/half due to component tolerances.
So I settled a version for 2x65V at 4R and a version for 2x80V at 8R.

In order to tame the noisy OTA of the IRS2092, all the LiteAmps are designed for large input signals (ranging from 6.5Vp to 8Vp for max.power).
The gain board offers differential inputs for typical line levels and is able to drive the LiteAmp to full power.
It also incorporates a limiter, which avoids amp clipping. (If not needed, the limiter can be skipped.)
Documentation has it focus on 2x40V, but includes the rules for adjustment to any other supply.

This Version has been shown in very detail over the previous part of the thread.
Possible operating range: 2x25V...2x42V
Max. power at stabilized 2x42V: 400W / 2R
Power with realistically sagging supplies, idling at 2x40V:
250W/2R, 130W/4R, 70W/8R

Slightly less audiophile than the 2x40V-version, but still better than average.
Attached harmonics measurements are for 1W and 200W.
Possible operating range: 2x50V...2x84V
Max. power at stabilized 2x84V: 400W / 8R
Power with realistically sagging supplies, idling at 2x80V:
250W/8R (not suited for 4R and 2R !)

Like the 2x80V, but over current protection allows operation at 4R.
Possible operating range: 2x40V...2x68V
Max. power at stabilized 2x68V: 500W / 4R
Power with realistically sagging supplies, idling at 2x65V:
300W/4R, 160W/8R (not suited for 2R !)
Attached Images
File Type: png 80V_IRFI4020_1W_8R.png (31.2 KB, 555 views)
File Type: png 80V_IRFI4020_200W_8R.png (31.3 KB, 552 views)
Attached Files
File Type: pdf LiteAmpGain_2x40V_Schematic20141124.pdf (95.6 KB, 241 views)
File Type: pdf LiteAmpGainBoardBOM20141121.pdf (256.6 KB, 154 views)
File Type: zip LiteAmpGainGerber20141121.zip (58.3 KB, 109 views)
File Type: pdf LiteAmp_2x40V_IRFI4212_Schematic.pdf (114.8 KB, 243 views)
File Type: pdf LiteAmp2x40V_IRFI4212_BomBuilderData.pdf (435.7 KB, 152 views)
File Type: pdf LiteAmp2x65V_IRFI4020_BomBuilderData.pdf (305.5 KB, 85 views)
File Type: pdf LiteAmp2x80V_IRFI4020_BomBuilderData.pdf (326.2 KB, 101 views)
File Type: zip LiteAmpMainGerber20140724.zip (77.3 KB, 116 views)

Last edited by ChocoHolic; 26th September 2015 at 12:45 PM. Reason: Typos
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