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Old 11th June 2007, 07:54 AM   #1
roender is offline roender  Romania
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Default Strange LTP cascoding circuit

What are the role of D501 and D503 in this schematic?
Have something to do with high tempco of jfet ccs?
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Old 11th June 2007, 08:10 AM   #2
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Roender,

Compensation..... helps trim OLG to near unity close to the pole.....

Hugh
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Old 11th June 2007, 08:18 AM   #3
roender is offline roender  Romania
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Thank you sir Hugh Dean

Can you be more specific, please.
It is hard to believe that 1n4148 diode can be used for frequency compensation

Mihai
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Old 11th June 2007, 10:23 AM   #4
AKSA is offline AKSA  Australia
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Mihai,

My mistake; I apologise, I was thinking of the highlighted capacitor between the LTP collectors!!'

These diodes are used to thermally compensate the BE junctions of TS15 and TS15 since both are fed from a current source and only one of the voltage reference diodes compensates the BE voltage of the CCS.

To be honest, I don't believe they are really necessary, particularly if you replaced the two diodes of the CCS with a green LED, which has almost the same tempco as the be junction of the CCS transistor.

Again, I'm sorry Mihai, I mistook the cap for your question!

Cheers,

Hugh
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