Hello everyone,
I am trying to design an amplifier for some physics experiment, it's not really for audio but I think audio amplifier designs is the closest thing to what I'm trying to do. Bandwidth needed is no more than 20KHz, with less than 40 milli amps load. However the need for output voltage swing is quite higher than audio amps: something between 600 and 800 V peak to peak.
I have simulated the typical design with an input stage consisting of a differential pair with current mirror at the collector, I noticed the differential pair sees almost half the entire output swing. Base and emitter are near 0 but collector is close to the negative rail. This bjt could work https://www.diodes.com/assets/Datasheets/ZXTP08400BFF.pdf but I am not sure it is meant to be used in a differential pair.
Should I try to isolate the input differential pair from seeing such high voltage difference between collector and base,emitter? Any ideas on how that could be done?
Thank you.
I am trying to design an amplifier for some physics experiment, it's not really for audio but I think audio amplifier designs is the closest thing to what I'm trying to do. Bandwidth needed is no more than 20KHz, with less than 40 milli amps load. However the need for output voltage swing is quite higher than audio amps: something between 600 and 800 V peak to peak.
I have simulated the typical design with an input stage consisting of a differential pair with current mirror at the collector, I noticed the differential pair sees almost half the entire output swing. Base and emitter are near 0 but collector is close to the negative rail. This bjt could work https://www.diodes.com/assets/Datasheets/ZXTP08400BFF.pdf but I am not sure it is meant to be used in a differential pair.
Should I try to isolate the input differential pair from seeing such high voltage difference between collector and base,emitter? Any ideas on how that could be done?
Thank you.
You can use a cascode in the collector side of the LTP.
But then the cascode needs to have >40V rating.
What devices are you planning to use for the VAS and output stages?
Looks to me that you will need 1000Vce0 devices !
Or maybe copy the valve/tube guys who insert an output transformer to change the output voltage. Instead of a step down output transformer you could use a step up transformer. A 1:4 step up means your amplifier could operate on +-100Vdc supplies
But then the cascode needs to have >40V rating.
What devices are you planning to use for the VAS and output stages?
Looks to me that you will need 1000Vce0 devices !
Or maybe copy the valve/tube guys who insert an output transformer to change the output voltage. Instead of a step down output transformer you could use a step up transformer. A 1:4 step up means your amplifier could operate on +-100Vdc supplies
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Do you *really* need an input differential pair?
Not indispensable if all you need is "an amplifier which can swing 800/1000Vpp and supply 40mA peak into load".
What will you be driving?
What range of frequencies? ... DC?
Do you need vanishing low distortion as in Hi Fi amplifiers or can stand, say, 1% or 2% distortion?
Because in that case you can build a simple power stage which can do the muscle work, and AC drive it through capacitors, separating the very high voltage output from a more reasonable input stage.
We need more details 😉
Not indispensable if all you need is "an amplifier which can swing 800/1000Vpp and supply 40mA peak into load".
What will you be driving?
What range of frequencies? ... DC?
Do you need vanishing low distortion as in Hi Fi amplifiers or can stand, say, 1% or 2% distortion?
Because in that case you can build a simple power stage which can do the muscle work, and AC drive it through capacitors, separating the very high voltage output from a more reasonable input stage.
We need more details 😉
you could use a tube output transformer to step up a 100w audio amp
8 ohm to 6K would deliver about that swing
8 ohm to 6K would deliver about that swing
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