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Class D Switching Power Amplifiers and Power D/A conversion

Hypex DLCP/UcD400 build
Hypex DLCP/UcD400 build
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Old 17th May 2018, 11:28 PM   #11
ChrisHill is offline ChrisHill  United Kingdom
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After spending a while planning my off-board LED PCB, it was turning into a mammoth board with an extraordinary number of components just to light some LEDs. So I had another change of plan and moved the individual LEDs back onto the adapter board. I still plan to take each individual signal off to a separate board to make the 'amalgamated' front panel LEDs, but that should be a much simpler affair since it won't also have to include the 3x6 individual LEDs.

So I'll need to bring a separate LED driver supply onto the adapter boards, which I've labelled VDR in the attached diagram. I'll use a screw terminal block so that it's easy to daisy chain this supply to my 6 adapter boards.

I'd appreciate a quick check on this schematic before I get too deeply into laying out the components on the PCB. R1, R3 and R5 are the current limiting resistors for the LEDs, with values TBD, R2, R4 and R6 are basically copied from Rayma's schematic - I guess they are current limiting for the transistors?? R7 is a pull-up resistor for the clipping signal - the other signals are internally pulled up. One thing I'd appreciate a check on is the relationship between R6 and R7 - which side of R6 should R7 connect? Looking at it now I think I may have it the wrong side.

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Old 17th May 2018, 11:35 PM   #12
rayma is offline rayma  United States
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Quote:
Originally Posted by ChrisHill View Post
I'd appreciate a quick check on this schematic
This should need only one resistor connected to the 2N2222 base, around 10k.
Clarify again, is that input signal ground if "go", and high if "no go"?

R1, R3, R5 should be (Vcc-2V)/0.01A in ohms, and 2 x (Vcc-2V) x 0.01A in watts.

Last edited by rayma; 17th May 2018 at 11:41 PM.
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Old 17th May 2018, 11:38 PM   #13
ChrisHill is offline ChrisHill  United Kingdom
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Quote:
Originally Posted by rayma View Post
The pull up should need only one resistor connected to the 2N2222 base, around 10k.
So R7, but not R6? What's the purpose of R2 and R4? Are they not current limiting for the transistors, and if so, doesn't T3 also need R6 to do the same job?
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Old 17th May 2018, 11:46 PM   #14
rayma is offline rayma  United States
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Quote:
Originally Posted by ChrisHill View Post
So R7, but not R6? What's the purpose of R2 and R4? Are they not current limiting for
the transistors, and if so, doesn't T3 also need R6 to do the same job?
The series resistors R2, R4, R6 between the input and the base convert the input voltage signals to current,
which drives the BE junction, which causes the transistor to turn on and conduct enough current to saturate,
causing the collector voltage to fall to a low value, around 0.2VDC.

Last edited by rayma; 17th May 2018 at 11:50 PM.
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Old 17th May 2018, 11:48 PM   #15
ChrisHill is offline ChrisHill  United Kingdom
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Quote:
Originally Posted by rayma View Post
Clarify again, is that input signal ground if "go", and high if "no go"?
The clipping signal is normally high (due to the pull-up resistor) and goes low when the signal is clipping (which is when I want the LED to light).

The Current Limiting signal is internally pulled up (to 5.6V I think), and goes low when the amplifier is current limiting (which is when I want the LED to light).

The 'Ready' signal is normally low, but goes high (internally pulled up to 5.6V) when the amplifier has shut down due to an error (i.e. NOT ready). I want the LED to light when the amplifier is ready, i.e. when the signal is low.
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Old 17th May 2018, 11:52 PM   #16
ChrisHill is offline ChrisHill  United Kingdom
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Quote:
Originally Posted by rayma View Post
The series resistors R2, R4, R6 between the input and the base convert the input voltage signals to current,
which drives the BE junction, which causes the transistor to turn on and conduct enough current to saturate,
causing the collector voltage to fall to a low value, around 0.2VDC.
Thank you - so shouldn't R6 be there to do the same job for T3? And I assumed R7 is needed as well because the clipping signal is an open collector which needs to be pulled up.
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Old 17th May 2018, 11:55 PM   #17
rayma is offline rayma  United States
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Originally Posted by ChrisHill View Post
I want the LED to light when the amplifier is ready, i.e. when the signal is low.
So a "low" input always means the LED should be on. Then the circuit logic is correct.
Now we need to be sure of the logic levels so the circuit will properly function.
What is "low" and what is "high", in volts?
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Old 17th May 2018, 11:58 PM   #18
rayma is offline rayma  United States
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Quote:
Originally Posted by ChrisHill View Post
Thank you - so shouldn't R6 be there to do the same job for T3? And I assumed R7
is needed as well because the clipping signal is an open collector which needs to be pulled up.
Yes, all the transistors need the series resistor connected to the base.

Any open collector device needs a pull up resistor. Connect it before
the series base resistor (directly to the device), not after the resistor.

Last edited by rayma; 18th May 2018 at 12:00 AM.
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Old 18th May 2018, 12:08 AM   #19
ChrisHill is offline ChrisHill  United Kingdom
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Quote:
Originally Posted by rayma View Post
So a "low" input always means the LED should be on. Then the circuit logic is correct.
Now we need to be sure of the logic levels so the circuit will properly function.
What is "low" and what is "high", in volts?
Yes, that's right - in all three circuits, the LED needs to be on when the signal is low.

For the clipping signal, the open collector which I have to pull up, the notes say that the low state has a maximum of 1V. The pull up voltage must not exceed 65V (I'm planning to use 15.6V), and the maximum output current is 100mA.

For the current limiting signal, the low state apparently has a minimum value of -0.7V. It is internally pulled up to a value that I think is limited to 5.6V by a zener diode. I'll post the schematic in a moment.

For the Amplifier Ready signal, the low state apparently has a minimum value of -0.6V. It is internally pulled up to 5.6V (similar schematic to the current limiting signal).
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Old 18th May 2018, 12:09 AM   #20
ChrisHill is offline ChrisHill  United Kingdom
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Quote:
Originally Posted by rayma View Post
Yes, all the transistors need the series resistor connected to the base.

Any open collector device needs a pull up resistor. Connect it before
the series base resistor (directly to the device), not after the resistor.
Thank you - that makes sense. So I had it wrong in my earlier schematic, as I suspected.
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