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Old 19th December 2012, 07:03 PM   #181
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Hi Reactance,
basically it is possible to feed the D-portion from the feedback through the
OPamp as shown in your schematic, but it is demanding for the OPamp.
In order to achieve a behavior similar to an ideal OPamp you will need something fast. Furtheron you have a loop with high impedances and high gain at high frequencies ==> critical with respect to self disturbance of the amp.

For these two reasons, I have chosen not to feed the D portion through the OP amp, but through the two BJTs in common base connection.
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Old 19th December 2012, 07:44 PM   #182
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Quote:
Originally Posted by ChocoHolic View Post
Hi Reactance,
basically it is possible to feed the D-portion from the feedback through the
OPamp as shown in your schematic, but it is demanding for the OPamp.
In order to achieve a behavior similar to an ideal OPamp you will need something fast. Furtheron you have a loop with high impedances and high gain at high frequencies ==> critical with respect to self disturbance of the amp.

For these two reasons, I have chosen not to feed the D portion through the OP amp, but through the two BJTs in common base connection.
Hi Choc man.

I have a few questions, with the two feedback nodes pre and post feedback, would it be useful to add compensation and add a LP pole just before the amplification stage which can aid as a HF band rejection filter or maybe an "Active filter and increase the number of poles" uhmm

Example a roll off of approx 600kHz in the HF switching region (depending on the switching frequency of course) this is to help with with modulation junk being injected into the power amplification stage.

Another idea i was thinking of (More protection)
Add a circuit that monitors the switching frequency coming from the modulator if the switching frequency is *NOT* in range within the design, shut the amp down.

what do you think ?
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Old 20th December 2012, 05:45 PM   #183
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Hi Reactance,
the pre filter feedback is just providing the hysteresis.
Regarding the neg feedback from post filter, please have a look to the considerations in the early postings of my thread about the SystemD MD.
It is up to you to experiment with your proposal, if you can reach good step response, low distortion, fit with normal OP amps and sufficient ruggedness vs self disturbance.

Shut down:
It is a question of philosophy. I prefer to spend components a circuit, which controls the output ripple via switching frequency and at the same time reduces distortion (==> dynamic hysteresis), rather than spending components to shut down when the frequency goes low. Shuting down is not a preferred situation, preferred is to have the amp playing the music.
Already the shut down with automatic restart in case of over current is a the limit what I can accept.
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Old 22nd December 2012, 01:08 PM   #184
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Today I found time for incoming inspection of the LM306.
1. We will definitely need a pull up at the output, because of the low sourcing capability of the LM306.
2. +5V for Vcc+ is not sufficient. It simply does not operate with that. At +12V everything is fine. Data sheet does not specify a min necessary Vcc+. +12V is recommended and you will find some data, when operated at +10V. So we can expect that any Vcc+ between +10V...+12V will be fine.
....will keep both topics in mind for the next update of schematic.
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Old 23rd December 2012, 04:32 AM   #185
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Choco,

I have no idea what made you to choose LM306 crappy comparator, when you have LM361 as a better alternative with 20nS response time, +/-15V front end supply & +5V logic vcc, push-pull complementary outputs and much lesser in cost.

Kanwar
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Old 23rd December 2012, 06:51 AM   #186
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Hi Kanwar,
you already said the reason.
I want to provide the option for a crappy comparator, which is easily available in DIP8.
LM160/360 and LM161/361 turned out out to be hard to get and furtheron TI completely canceled the related DIP8 versions. Portfolio clearing after company fusions always kills the best products...
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Old 23rd December 2012, 11:15 AM   #187
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Quote:
Originally Posted by ChocoHolic View Post
Hi Kanwar,
you already said the reason.
I want to provide the option for a crappy comparator, which is easily available in DIP8.
LM160/360 and LM161/361 turned out out to be hard to get and furtheron TI completely canceled the related DIP8 versions. Portfolio clearing after company fusions always kills the best products...
Agreed but one can make a DIP adapter for SMD comparator and use it to evaluate other comparators as well.

But its DIP version is available here at Newark/Mouser/Digikey

LM361N/NOPB - NATIONAL SEMICONDUCTOR - IC, DIFFERENTIAL COMP, SINGLE | Newark

LM361N/NOPB Texas Instruments | Mouser

LM361N/NOPB Texas Instruments | LM361N/NOPB-ND | DigiKey
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Old 23rd December 2012, 02:15 PM   #188
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After rechecking why I did not put it to my preferred list - I agree on the LM361. For this type the DIP seems to remain uncanceled - so this was not the reason.
Main concern on LM361 was that it is 14 PIN, wasted for 3x NC and two strobes which we do not need. Nevertheless, I am starting to consider it again.
You think I should enable the PCB even for LM361, NE529?

...would mean overall: LT1016, MAX913, LM306, LM361, NE529 and with SOIC adaptors even more.
@all: Please drop your opinion whether I should add the LM361, NE529.
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Old 24th December 2012, 04:26 AM   #189
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Yes, please add LM361
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Old 26th December 2012, 09:36 AM   #190
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Hm, in the layout this triple comparator thing will consume slightly more space, but should be possible.
I found another critical point: Sensing of the OCP might become headache, with the series diodes inside the sensing loops.
...will reconfigure a little bit... sensing of high side... and might move the series diode of the low side towards the source instead of drain...
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