class D amp

I don't know the TPA3251... Says 13.2 V_max?,  maybe you mean the 
tpa3221?  

Is it a one of?  (I would do class A, a heat sink and fan...
('cause that's what I know.))
Is the class D partly for fun and future profit?  

George H. 

John Larkin wrote:

---------------------------

> I want to build an AC source to test synchros/resolvers/RVDTs. The
> target is 400 Hz 30 VRMS at maybe 30 VA, but we might want to simulate
> aircraft "wild power" and drive LVDTs, so maybe 250 Hz to a few KHz.
> 
> I'm thinking of using half of a TPA3251 audio amp and a step-up
> transformer. Like this maybe:
> 
> https://www.dropbox.com/s/eikiu79jv4cjxqp/P548_WB_1.JPG?raw=1
> 
> The transformer DCR is low, so a blocking cap might be prudent to
> prevent DC current in the primary. I have a cute little 1000 uF 2.5V
> polymer cap in stock, so I could use a few of those in parallel. The
> diodes keep the cap from exploding if the h-bridge ever rails.
> 
> How does that look? Any advice?
> 

** I designed a very similar set up for producing 240VAC with variable frequency and enough power to operate the synchronous motor in a TT - it was published in Electronics Australia mag in July of 1998. Output power came from a TDA1514A and step up from a standard 240V to 9V, 30VA toroidal operating in reverse. 

The obvious problem is core saturation, if the input frequency goes too low PLUS inrush surge if the drive signal starts suddenly or is interrupted. The variable sine wave oscillator was on the same PCB and thus permanently connected. 

Powering up produced misbehaviour of the power IC which was solved by adding a fade-up feature in the signal path consisting of a red LED and CdS cell. The cell was in series with the signal and the LED came on delayed and gradually but would go out fast if the supply was interrupted. A few diodes, a zener and a 1000uF cap did the job.



..... Phil 



 

 






> I've heard horror stories about "the devil's staircase" progressive
> saturation, which I don't really understand. The transformer is a
> toroid, low resistance and pretty dramatic saturation behavior.
> 
> 
> -- 
> 
> John Larkin         Highland Technology, Inc
> picosecond timing   precision measurement 
> 
> jlarkin att highlandtechnology dott com
> http://www.highlandtechnology.com

 George Herold wrote:

-------------------------
>
> I don't know the TPA3251... Says 13.2 V_max?,  maybe you mean the 
> tpa3221?  
>


** FFS learn to READ !!! 

 13.2V is the *analog* supply. 

 The class D power stage spec is 36V  !! 


> 
> Is it a one of?  (I would do class A, a heat sink and fan...
> ('cause that's what I know.)

** Class A ???  WTF for ? 
 
   Class AB not good enough for you ? 


> Is the class D partly for fun and future profit?  


** It almost eliminates the need for a heatsinking. 

   Only a $10 part but rather complex to use. 


.....  Phil 

On Friday, August 11, 2017 at 9:09:37 PM UTC-4, Phil Allison wrote:
> George Herold wrote:
> 
> -------------------------
> >
> > I don't know the TPA3251... Says 13.2 V_max?,  maybe you mean the 
> > tpa3221?  
> >
> 
> 
> ** FFS learn to READ !!! 
> 
>  13.2V is the *analog* supply. 
> 
>  The class D power stage spec is 36V  !! 

Ouch, sorry Phil, no need to yell.  
(I only looked at the first stage of the spec 
sheet and misunderstood.)  
> 
> 
> > 
> > Is it a one of?  (I would do class A, a heat sink and fan...
> > ('cause that's what I know.)
> 
> ** Class A ???  WTF for ? 
>  
>    Class AB not good enough for you ? 
Sorry, my own hammer/nail problem.  I've  used someone else's  
AB and complained about the cross-over.  
(I'm assuming you by class AB you also mean a push-pull output.)
(Well i've done push-pulls for one of stuff, just never sold one.)

> 
> 
> > Is the class D partly for fun and future profit?  
> 
> 
> ** It almost eliminates the need for a heatsinking. 
Of course, I mean I don't know a lot, but I'm not a 
complete idiot.  
> 
>    Only a $10 part but rather complex to use. 

Complex from the micro-p programming side...
(ignore that I'll go read the spec sheet.)

George H. 
> 
> 
> .....  Phil

On 08/11/2017 04:27 PM, John Larkin wrote:
> 
> I want to build an AC source to test synchros/resolvers/RVDTs. The
> target is 400 Hz 30 VRMS at maybe 30 VA, but we might want to simulate
> aircraft "wild power" and drive LVDTs, so maybe 250 Hz to a few KHz.
> 
> I'm thinking of using half of a TPA3251 audio amp and a step-up
> transformer. Like this maybe:
> 
> https://www.dropbox.com/s/eikiu79jv4cjxqp/P548_WB_1.JPG?raw=1
> 
> The transformer DCR is low, so a blocking cap might be prudent to
> prevent DC current in the primary. I have a cute little 1000 uF 2.5V
> polymer cap in stock, so I could use a few of those in parallel. The
> diodes keep the cap from exploding if the h-bridge ever rails.
> 
> How does that look? Any advice?
> 
> I've heard horror stories about "the devil's staircase" progressive
> saturation, which I don't really understand. The transformer is a
> toroid, low resistance and pretty dramatic saturation behavior.
> 

Why even filter prior to the xfrmr at all? Since you're going to be 
generating the signal using DDS on a uP anyway, why not use a part like:

<http://www.ti.com/lit/ds/symlink/tas5612la.pdf>

that takes a PWM input to begin with? Then you get significantly lower 
offset voltage specs and should be able to ditch all the caps n such on 
the primary side and not worry about that "devil's staircase" stuff.

Intuitively it seems like you'd get the best performance by keeping 
everything digital/PWM until the last moment via an LC on the secondary 
side.

George Herold wrote:

----------------------



> > >
> > > I don't know the TPA3251... Says 13.2 V_max?,  maybe you mean the 
> > > tpa3221?  
> > >
> > 
> > 
> > ** FFS learn to READ !!! 
> > 
> >  13.2V is the *analog* supply. 
> > 
> >  The class D power stage spec is 36V  !! 
> 
> Ouch, sorry Phil, no need to yell.  


** Hardly your first such offence - pal. 



> > > 
> > > Is it a one of?  (I would do class A, a heat sink and fan...
> > > ('cause that's what I know.)
> > 
> > ** Class A ???  WTF for ? 
> >  
> >    Class AB not good enough for you ? 
>
> Sorry, my own hammer/nail problem.  I've  used someone else's  
> AB and complained about the cross-over. 
>


** This class AB amplifier IC from ST is my weapon of choice: 

  http://www.st.com/content/ccc/resource/technical/document/datasheet/4f/18/a6/c8/21/33/41/8d/CD00001887.pdf/files/CD00001887.pdf/jcr:content/translations/en.CD00001887.pdf




..... Phil 

On Fri, 11 Aug 2017 18:09:29 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

> George Herold wrote:
>
>-------------------------
>>
>> I don't know the TPA3251... Says 13.2 V_max?,  maybe you mean the 
>> tpa3221?  
>>
>
>

>
> 13.2V is the *analog* supply. 
>
> The class D power stage spec is 36V  !! 
>
>

No, No, it's 50 volts max. Or maybe 38.

>** FFS learn to READ !!! 


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On Fri, 11 Aug 2017 22:05:03 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>On 08/11/2017 04:27 PM, John Larkin wrote:
>> 
>> I want to build an AC source to test synchros/resolvers/RVDTs. The
>> target is 400 Hz 30 VRMS at maybe 30 VA, but we might want to simulate
>> aircraft "wild power" and drive LVDTs, so maybe 250 Hz to a few KHz.
>> 
>> I'm thinking of using half of a TPA3251 audio amp and a step-up
>> transformer. Like this maybe:
>> 
>> https://www.dropbox.com/s/eikiu79jv4cjxqp/P548_WB_1.JPG?raw=1
>> 
>> The transformer DCR is low, so a blocking cap might be prudent to
>> prevent DC current in the primary. I have a cute little 1000 uF 2.5V
>> polymer cap in stock, so I could use a few of those in parallel. The
>> diodes keep the cap from exploding if the h-bridge ever rails.
>> 
>> How does that look? Any advice?
>> 
>> I've heard horror stories about "the devil's staircase" progressive
>> saturation, which I don't really understand. The transformer is a
>> toroid, low resistance and pretty dramatic saturation behavior.
>> 
>
>Why even filter prior to the xfrmr at all? Since you're going to be 
>generating the signal using DDS on a uP anyway, why not use a part like:
>
><http://www.ti.com/lit/ds/symlink/tas5612la.pdf>
>
>that takes a PWM input to begin with? Then you get significantly lower 
>offset voltage specs and should be able to ditch all the caps n such on 
>the primary side and not worry about that "devil's staircase" stuff.
>
>Intuitively it seems like you'd get the best performance by keeping 
>everything digital/PWM until the last moment via an LC on the secondary 
>side.

Sometimes the signal could come from our VME module, so I need the
option to accept an analog input.

The LC on the primary keeps the HF stuff out of the toroid. I'd expect
it to be very lossy at 600 KHz.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

John Larkin wrote:

------------------------------
>
> >>
> >> I don't know the TPA3251... Says 13.2 V_max?,  maybe you mean the 
> >> tpa3221?  
> >>
>  
> >
> > 13.2V is the *analog* supply. 
> >
> > The class D power stage spec is 36V  !! 
> >
> >
> 
> No, No, it's 50 volts max. Or maybe 38.
>
>

** TI say 36V is the safe max. 

 50V is *absolute max* not recommended for actual use.

 The data sheet make this very clear, Mr Pedant.  




.....  Phil 

I would use the transformer to generate a 90V DC voltage on the secondary side. Then add the class D circuit on the output instead 

No staircasing, and very simple filter

You can do an unregulated DC/DC converter which simplifies the converter. It would add more active components since you need a half bridge and 2 diodes on the converter

You would need communication across the barrier, but you need that anyway to monitor the output voltage 

Cheers

Klaus