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Old 2nd May 2013, 11:32 PM   #21
Telstar is offline Telstar  Italy
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Old 2nd May 2013, 11:55 PM   #22
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If SPICE models are the reason simulated performance is worse, try using these models for the C5200/A1943 and C5171/A1930:

New 2SC5200 and 2SA1943 SPICE models

Finding SPICE Models
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Old 3rd May 2013, 08:19 AM   #23
astx is offline astx  Austria
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Default Output protection / SOA

Attached a SOA plot of 8, 4, 2 R load. Short circuit starts too late at about 1.7R load.
Sorry - my fault :
I changed the emitter resistor values the last days from 0.22R to 0.47R and adapted the short circuit values not correctly.
Thanks michaelkiwanuka for reporting this to me.
Give me some time to correct these values - or feel free to help here.

BR,

Toni
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File Type: png 2ef_soa_simulation.png (136.5 KB, 1078 views)
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Old 3rd May 2013, 08:20 AM   #24
astx is offline astx  Austria
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Quote:
Originally Posted by keantoken View Post
If SPICE models are the reason simulated performance is worse, try using these models for the C5200/A1943 and C5171/A1930:

New 2SC5200 and 2SA1943 SPICE models

Finding SPICE Models
Thank you - will try these models on weekend!

BR, Toni
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Old 3rd May 2013, 10:32 AM   #25
AndrewT is offline AndrewT  Scotland
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where is R79?
The output stage and the feeds to the protection are hidden.

Ratio of R22 to R56 is liable to entering triggering while still handling a valid audio signal into a valid audio load. R56 > R22*2 and preferably 3times to 4times. 27>12*2
If you split R22 into R22a+r22b=R22 and tap of the junction, you can experiment with different R22a:R56 ratios.
R22a < 27/3 or < 27/4 will delay the onset of triggering and still protect the VAS from overheating.
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Last edited by AndrewT; 3rd May 2013 at 10:37 AM.
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Old 3rd May 2013, 11:18 AM   #26
astx is offline astx  Austria
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Quote:
Originally Posted by AndrewT View Post
where is R79?
The output stage and the feeds to the protection are hidden.

Ratio of R22 to R56 is liable to entering triggering while still handling a valid audio signal into a valid audio load. R56 > R22*2 and preferably 3times to 4times. 27>12*2
If you split R22 into R22a+r22b=R22 and tap of the junction, you can experiment with different R22a:R56 ratios.
R22a < 27/3 or < 27/4 will delay the onset of triggering and still protect the VAS from overheating.
If you can't open the asc file: R79 in ltspice simulation file is R53 in the schematic picture in post #1.

Thx for checking VAS load.

Will check your findings at weekend.

BR, Toni
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Old 3rd May 2013, 12:24 PM   #27
astx is offline astx  Austria
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Default Simulation of VAS short circuit protection

why the hell is there a trigger spike at 7,37V Voutput. Sim error?
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Old 3rd May 2013, 12:26 PM   #28
AndrewT is offline AndrewT  Scotland
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check operation of Q37.
By the time you apply 400mVbe there will be some triggering effect building up.
That why I said 3 to 4 times for that resistor ratio.

It might be something else.
Check the output protection. Again 400mVbe could be approached at that particular point in the waveform.
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Old 3rd May 2013, 12:47 PM   #29
astx is offline astx  Austria
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Quote:
Originally Posted by AndrewT View Post
check operation of Q37.
By the time you apply 400mVbe there will be some triggering effect building up.
That why I said 3 to 4 times for that resistor ratio.

It might be something else.
Check the output protection. Again 400mVbe could be approached at that particular point in the waveform.
You are correct - the output protection is the source of this trigger spike. Sim load was 4R.

We have to do some rework to meet the SOA of the 2 EF stages to drive 4R loads. A lower supply voltage is required for safe 4R usage.

BR, Toni
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Old 3rd May 2013, 01:03 PM   #30
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by astx View Post
........A lower supply voltage is required for safe 4R usage.......
Is this true?

Or do you mean that the transient pass capability of the protection threshold needs to be increased to closer match the output device capability for short term transients.
The DC SOAR is very different from the transient SOAR.
The protection locus should take account of this.
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