Hi,
Could you please list all your requirements. Searching through a couple of posts/threads to find out what you want to achieve needs a lot of time.
Voltage range, current range, frequency range, waveform .... and so on
And an additional draft could also help to clarify things.
It's not clear what you mean by "ClassAB for current and voltage amplifier"
Independent of amplifier class ... the (filtered) output will follow the input signal and will amplify voltage as well as current.
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.
For example: in an AB amplifier all reactive load power needs to be dissipated as heat, with an class D amplifier it is pused between load and DC supply path of the amplifier.
Connecting a C to an AB amplifier causes much heating ... but with a class D amplifier the heating is low.
The average current in a class D DC supply is low (but the AC current, RMS may be fairly high)
*****
Maybe you want 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.
Klaus
Does this mean you want to build a "current amplifier"? ... where with varying load resistance it automatically adjusts output voltage to get constant output current? = amplifier with "current" as feedback value?Now let us move to a individual solution on for "Current"( what you have said loop)
Waveform = sine?1. The amp input should be plus and minus 7volt AC, 45-65Hz( 1 Hz has been converted to 1024)
DC? Single supply?2. Amp operating voltage should be more or less 24v.
What do you mean by "single channel" and "both side"?3. Only single channel "current" signal should be amplify on both side.
If sinewave: do you mean 16.5V RMS?5. Output should be 16.5 V/1.5 A. 25 Watt.
This could mean a lot.6. SC protection and current sensing capabilities.
I'm also confused with this. A CT usually has no "input voltage specification" .. because it just "sees" the current.CT, current transformer primary winding has to be 16.5 V/1.5 A(Amplified signal), secondary should have 4.125v/6A output!
Take a look my previous work in form of ClassAB. Darlington pair brings current.Sadly still there is a lot unclear to me.
I strongly recommend to draw a draft of what you want to achieve. Some kind of block diagram where we can see signal flow, amplifier filter (if any), feed back (if any), and so on.
Overcome "heating and avoiding crossover distortion"Even the most important is unclear to me: What's your target...
See the dia gram kindly. Yes its has feedback, shunt, high frequency cancelation.Does this mean you want to build a "current amplifier"? ... where with varying load resistance it automatically adjusts output voltage to get constant output current? = amplifier with "current" as feedback value?
SureWaveform = sine?
May be. Some one suggest me this kind of application.DC? Single supply?
--> If yes, then this means you need full bridge output topology.
From my STM 32 board 2 channel current and voltage signal, comes from D8812 may be.What do you mean by "single channel" and "both side"?
May be peak to peak 16.5V( just after amplification)If sinewave: do you mean 16.5V RMS?
This equals to +/-23.33V.
--> This would mean a too low margin to a 24V DC supply.
After amplification. 25W may not currect.25W on an ohmic load of 7.5 ohms gives 13.69V RMS and 1.83V RMS. How does this comply with your 16.5V / 1.5A?
This could mean a lot.
Short circuit protection. What do you want to protect? Mainly the load, or mainly your amplifiers output stage?
How should it work? Like a fuse ... to stop operation until the user resets? In hickup mode ... in a way that it stops operation, but automatically retries? Just as limiter ... how fast? Before or after the filter?
I'm also confused with this. A CT usually has no "input voltage specification" .. because it just "sees" the current.
And usually the output current is much less than the input current (let's say in a range of 5mA ... 100mA depending on type), but in your case it is the other way round.
Did you go through usual CT datasheets and CT application notes? If not, please do this to understand operation.
So if you need exactly this .... why don't you just replace the AB stage with a class D stage with filter?I need exactly those parameters to amplify my signal
The question was: "current feedback" vs "voltage feedback". But it's clear now.Yes its has feedback,
For you. But there are milllion applications that don't use sine shape.Sure
OK. Full bridge class D. For sure you know this schematic is not complete. The whole Mosfet gate control is missing.May be. Some one suggest me this kind of application.
I completely don't understand what this means...and how it is involved in class D problem..From my STM 32 board 2 channel current and voltage signal, comes from D8812 may be.
I only partly agree.A transformer causes a phase shift at low frequencies caused by its inductance.
Dont you mean input high pass filter.So if you need exactly this .... why don't you just replace the AB stage with a class D stage with filter?
Well noticed! In case of current, R1 and C1 has contribution for attinuation.Btw: you say your input frequency is 45Hz ...65Hz, but I see your input high pass filter cutoff freqency is about 160Hz.
.nd now I see your transformer. This is no "classical CT". It rather is a classical power transformer.
A classical CT has sinle turn primary winding and high turn count secondary winding. For sure there may be others.
Classical CT's are not meant to transfer power...and don't need to be efficient
I only partly agree.
In your case what counts is the pri--> sec phase shift, not the V-->I phase shift.
For the pri-->sec phase shift only the (small, series) stray inductance counts. Phase shift is small, but may increase with load current.
(For V-->I phase shift the big parallel inductance counts, phase shift will decrease with load current)
Pri--> sec phase shift is low. Depending on transformer in the low microseconds. For sure you need to take care of it to ensure amplifier stability. I recommend that your circuit operates only to a given frequency in "current feedback mode" and then turns over to "voltage feedback mode" to ensure stability.
So did we agree you're looking for a current regulated class-D amplifier? Any specs for distortion, accuracy or bandwidth (I see now ~60hz?)
It's conceptually easy to wrap a voltage mode controlled amplifier in a current regulation loop, but it's very hard to get good performance if the load has wide variation. Current loop gain in a voltage mode supply depends on load and approaches infinity into a short circuit. Thus the loop must have limited gain if it's going to be stable into a short and would have poor performance into other loads.
You'll find almost no resources on "current mode controlled" class-D but the good news is that standard buck converter techniques work fine (peak, hysteric, average) in general with a class-D full bridge. But you're probably on your own implementing it (no controllers that I'm aware of).
7http://www.ti.com/lit/ds/slus283/slus283.pdf
No, output low pass filter. Connected to the output if tge class D amplifier to make the digital PWM signal a smooth analog signal.Dont you mean input high pass filter.
Why do you bother with complicated class D block diagranms, when there are ready to buy class D amplifiers.Lets post a basic classd dia gram. Do you want me to follow this basic?
I can't see what the amplifier classes have to do with the conduction phases.Phase shift is a reason. Now lets take a look how amplifiers conduction phase varies, does not it relavant ? How slow transformer can pick signal!
Okay. For the previous ClassAB I want to remember that "The first difference between voltage feedback and current feedback—the input impedance of current feedback op-amp inputs is very different. Because the inverting input has low impedance"No, output low pass filter. Connected to the output if tge class D amplifier to make the digital PWM signal a smooth analog signal.
You need the filter, because you need the current feedback signal from the analog signal.
I see no way to get useful current feedback from the PWM pulses.
Not sure what you wanna say!Then just replace your AB amplifier with the class C amplifer and filter.
Okay fine.As written above: just replace the AB amplifier.
I don´t know if this can simulatate, but I gues: yes.Dont you think, this kind of circuit I could simulate
Maybe you want to spend some time to draw an overview of your system: difference amplifier, class AB amplifier, current measurement, load.Not sure what you wanna say!
Current mode control IME is about load-step response.
Class D doesn't have load steps per se, only as much as
output voltage dictates against the fixed(ish) load.
What benefit does anyone claim for current mode control
in a Class D amplifier application, vs. simple voltage mode
(or even open loop direct analog-to-PWM)?
Can you change its frequency range to 45-60Hz? Suggest me a slower medium. Read the post from top to bottom kindly.It's practical to set a faster carrier frequency. CD quality is 41kHz. You get better fidelity, and you can use a lower value inductor.
Can you change its frequency range to 45-60Hz?
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