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Old 16th April 2012, 10:18 AM   #101
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Quote:
Originally Posted by Lazy Cat View Post
Mostly any 5 mm IR LED is okay.

At current If=3,5 mA, forward IR LED voltage is app. 1,2 V and that is too low for proper cascode, so please provide two of them in series on the PCB. That will provide Vce=1,8V for VAS BC transistor.
Ok i will do the modification.

Marc
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Old 16th April 2012, 10:18 AM   #102
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what is the benefit from the BIGBT...??
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Old 16th April 2012, 10:40 AM   #103
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Quote:
Originally Posted by MiiB View Post
what is the benefit from the BIGBT...??
Hi MiiB

Mhmm I simply love this BIGBT

Easy to drive (low input gate capacitance) output transistor (yes I consider BIGBT as one joint part only), very stabile output transistor as integrity (balanced conditions for NPN/PNP), IRF conduct only one base current for both outputs, so for one base current (and it is the same for both outputs) through IRF driver you get two parallel collector curents for the output (doubled hFE). Linear transconductance dIout/dVg, high speed ... you should try it once.

Last edited by Lazy Cat; 16th April 2012 at 10:44 AM.
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Old 16th April 2012, 01:09 PM   #104
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Exclamation TSSA BIGBT HP update

Update released

Changes:

- VAS cascode - two IR LED per cascode
- "ON" RED LED added - indicates bias-on state

Regards Andrej
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Old 16th April 2012, 03:22 PM   #105
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Quote:
Originally Posted by AndrewT View Post
the simplest !

post71 shows ~75 components.
I couldn't even count it.
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Old 16th April 2012, 03:24 PM   #106
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What happens when R6 and R7...are modulated with the input signal...??
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Old 16th April 2012, 03:51 PM   #107
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R6, R7 are voltage dumpers to CCS, necessary to use because 2N j-fets have too low Vds/power dissipation specs. Current through R6, R7 is constant as CCS-s are capable of, so ideally no modulation should be present on these resistors. Of course it would be better to use source/sink transistors without voltage dumpers (double cascoded CCS). CCS are not ideal and there's always tendency to have increasing level of distortions according to higher frequencies. Separate measurements of CCS shows their capability to maintain the current to be constant. If you suggest to replace the resistors with improved CCS-s you are invited to do so.

Possible ripple suppression would be to add small parallel caps across R6, R7, just to prevent AC modulation (low level ripple) as voltage drop on them.

Last edited by Lazy Cat; 16th April 2012 at 04:00 PM.
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Old 16th April 2012, 03:54 PM   #108
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Quote:
Originally Posted by terranigma View Post
I couldn't even count it.
Question
Quote:
Originally Posted by Bigun View Post
jeez, this is supposed to be the Simplest ? I think this thread has lost the plot along the way. Pitty, I like really simple.
Answer
Quote:
Originally Posted by Lazy Cat View Post
Hi Bigun

I can not manage more than two threads simultaneously, so logically one would be full of stuff.

From simple to more complex version, all based on the same TSSA base core. It is the same like in school, gradually progressing the knowledge.

Regards Andrej
I hope you find it reasonable.
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Old 16th April 2012, 04:52 PM   #109
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what if you reverse the positions.. so you place the resistors at the rails and the current sources where they belong. then you get both....reduced dissipation and no signal induced current modulation.
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Old 16th April 2012, 06:07 PM   #110
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Think you should rearrange the driven VAS cascode... make the connection inside the Rail resistors for the input pair.
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