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"Current" control is a big issue using ClassD ?

Hi there,

I think people who works in 'Analog or Power electronics" understand this issue.
I am having a project on, "3 phase power Calibrator"

Like my previous post I was trying to go with a ClassAB for current and voltage amplifier.https://www.edaboard.com/showthread.php?386525-Lets-take-a-look-on-a-linear-amplifier

Comparable study shows, ClassAB is less suitable than ClassD.
ClassD is a voltage source device, so current transformer may not be use, https://www.diyaudio.com/forums/class-d/343198-class-amplifier-suitable-60hz-potential-transformer.html#post5927022

I think potential transformer can be use with ClassD, https://www.element14.com/community/thread/73845/l/classd-amplifier-for-transformer


Since my project need to get Current transformer output, kindly suggest me what should I do.
I'am not sure with this solution,https://e2e.ti.com/support/motor-drivers/f/38/t/848028
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Your fundamental concepts are wrong.

All common DC / brushless DC machine tool servo drives use current control and they are PWM based; what would be called class D it it were used for audio.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Your block diagram is nonsensical; it shows voltage output without defining the current requirement and current output without defining the voltage requirement.

"Impedance matching" without defining impedances!
 

kubeek

Well-Known Member
Most Helpful Member
Your requirements make no sense. Do you mean you need current output, instead of current transformer output?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Your block diagram is nonsensical; it shows voltage output without defining the current requirement and current output without defining the voltage requirement.

"Impedance matching" without defining impedances!
None of his threads have ever made any sense, and he ignores any replies - as far as I'm aware he's still insisting that you can have constant current and constant voltage at the same time (other than with a constant load).
 

kubeek

Well-Known Member
Most Helpful Member
Well, technically a power callibrator does produce constant current and constant voltage at the same time, but it is not into the same load. So he needs three plus three AC outputs.
AFAIK they are used to produce voltage to one set of contacts and current to another set of contacts of a utility power meter, with the ability to have phase difference between the current and voltage and to set imbalance in the three phases.
 

audioguru

Well-Known Member
Most Helpful Member
Hasan does not understand that ALL modern audio amplifiers, class-AB or class-D are voltage source devices because their output voltage does not change when the load resistance changes, but limit the maximum amount of output current.
Also, all modern audio amplifiers do not use an output transformer.
 
None of his threads have ever made any sense, and he ignores any replies - as far as I'm aware he's still insisting that you can have constant current and constant voltage at the same time (other than with a constant load).
Your block diagram is nonsensical; it shows voltage output without defining the current requirement and current output without defining the voltage requirement.

"Impedance matching" without defining impedances!

I wanted to say a "current regulation loop" (which ideally has infinite output impedance)
.. or a "voltage regulation loop" (which ideally has zero output impedance)
It should be obvious that you can't have both at the same time
 
Also, all modern audio amplifiers do not use an output transformer
Thats what people get confused!

As you have expertise on Audio over 60 years, lets talk some basic.
Let me post a similar application schemetic where user wanted to do some thing !
This application is for 400W ( forget my application right at this moment) , user said " I have connected additional parallel resistors to R117A, R118A, R17A, because amp was clipping, when power supply was circa 2x35V, is possible that leads of that resistors was to long?"

iraudamp7d_schematic_1_full.png


Now lets see other ( attached 2)

The main part of this protection circuit is a transistor FET which is connected in the power supply branch amplifier integrated circuit IRS2092. When applying a positive voltage to the control electrode of the transistor, the ground power supply voltage and the comparator halts the modulation process. The transistor FET is switched on the circuit that brings together a number of protections. One of them is check the power supply, which detects whether the supply voltage is in the range of 68 to 100 volts. If this the condition is not met, the class d protection will react. Additional protection is temperature. Circuit controls the voltage on the thermistor, which is located on the heatsink of the power switching Mosfet. Last class d amplifier protection detects the amplified audio signal at the output of the amplifier and responds when congestion or limitation.


400w-claas-d-amplifier-schematic-irs2092-class-d-amplifier-protection.png


Whats in your mind to apply this kind of circuit?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
I wanted to say a "current regulation loop" (which ideally has infinite output impedance)
.. or a "voltage regulation loop" (which ideally has zero output impedance)
It should be obvious that you can't have both at the same time
Sorry, but that is again total nonsense - the amp output impedance needs to be low enough to provide the load current regardless of the feedback control being via current or voltage.


Any suitable power amplifier (DC coupled if appropriate for the load frequency) can be configured either way, depending how you derive the feedback:

Directly from the output for voltage control, or across a shunt (or some form of current transducer) which is in series with the load, for current control.

Voltage control:

Current control:
 
Sorry, but that is again total nonsense - the amp output impedance needs to be low enough to provide the load current regardless of the feedback control being via current or voltage.


Any suitable power amplifier (DC coupled if appropriate for the load frequency) can be configured either way, depending how you derive the feedback:

Directly from the output for voltage control, or across a shunt (or some form of current transducer) which is in series with the load, for current control.

Voltage control:

Current control:
Not sure why you have raised this issue that had been "in general" and "off topic".

Keep your eyes "to the point".
This post is dedicate to know how CT can be implemented on classD, if its provide enough current. Unfortunately : its limiting the current.
Read what Audioguru said " class-AB or class-D are voltage source devices because their output voltage does not change when the load resistance changes, but limit the maximum amount of output current."
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Keep your eyes "to the point".
This post is dedicate to know how CT can be implemented on classD, if its provide enough current. Unfortunately : its limiting the current.
Read what Audioguru said " class-AB or class-D are voltage source devices because their output voltage does not change when the load resistance changes, but limit the maximum amount of output current."
To be blunt, the point is that you do not understand basic electronics principles.


To control current through any real-world load - which will have some finite resistance or impedance - you can control the voltage drive across that and some form of current feedback sense resistor or transducer.

That in some variation is how pretty much all amplifier plus current control systems work, from small LED drivers to motor controllers rated at tens or hundreds of kilowatts.

Current sense resistor in series with the load, in a small circuit rated at a few watts:
Led-Driver.jpg

The current feedback sense resistor in a servo drive we have on the bench at the moment (in the 5 - 10KW range), which is connected directly in series with the load:
IMG_9874a.jpg

The blue item in this photo are the current transducers use for feedback in a rather larger servo drive (possibly 50 - 100KW), again in the current path to the load:
fanuc_cts.jpg

Those are all variations of switched mode or PWM power systems, which could be called Class D if intended for audio.


My company has been installing and repairing such equipment for several decades and I have an extremely good understand of how such power control systems operate.

As you insist things do not work as they factually do, there is no point continuing.
Again - I'm done.
 
To be blunt, the point is that you do not understand basic electronics principles.


To control current through any real-world load - which will have some finite resistance or impedance - you can control the voltage drive across that and some form of current feedback sense resistor or transducer.

That in some variation is how pretty much all amplifier plus current control systems work, from small LED drivers to motor controllers rated at tens or hundreds of kilowatts.

Current sense resistor in series with the load, in a small circuit rated at a few watts:
View attachment 121287

The current feedback sense resistor in a servo drive we have on the bench at the moment (in the 5 - 10KW range), which is connected directly in series with the load:
View attachment 121285

The blue item in this photo are the current transducers use for feedback in a rather larger servo drive (possibly 50 - 100KW), again in the current path to the load:
View attachment 121286

Those are all variations of switched mode or PWM power systems, which could be called Class D if intended for audio.


My company has been installing and repairing such equipment for several decades and I have an extremely good understand of how such power control systems operate.

As you insist things do not work as they factually do, there is no point continuing.
Again - I'm done.
My God is Kind enough that you have " stop". Thanks.
 

audioguru

Well-Known Member
Most Helpful Member
The two Mosfet class-D 400W audio amplifiers you showed have no control of the output current. If the current becomes too high then they overheat or the amplifier and/or the power supply become destroyed.

I think you need a current transformer for isolation so that it can sense the current in the high voltage secondary output of the output transformer you are using. The primary of the current transformer will be in series with the high voltage load.

You do not need a current transformer if you sense the current through a low value resistor in series between the amplifier output and the primary of the output transformer.
 
The two Mosfet class-D 400W audio amplifiers you showed have no control of the output current. If the current becomes too high then they overheat or the amplifier and/or the power supply become destroyed.
Sure. Since, FET or MOSFET works same here( They have some differences). Last post you suggest me to find a classD which provide more current.
Now take a look my ClassAB which is used for current AMP, it has shunt, it has feedback .....see how darlington works

current_ab_amp.PNG

I think you need a current transformer for isolation so that it can sense the current in the high voltage secondary output of the output transformer you are using. The primary of the current transformer will be in series with the high voltage load.
Kindly post a similar circuit ! or reference.

The filtered output of a class D should be identical to the output of a class AB (except side effects like distortion, noise, phase shift...)
This is true for voltage as well as current.
The difference between both is how the signal is generated within the amplifier... and the expected power dissipation.
 

audioguru

Well-Known Member
Most Helpful Member
I do not know what you are doing with a voltage amplifier and a current amplifier.
 

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