Hello everybody!
I'm trying to build an arbitrary signal generator for my lab.
To make things interesting, for a first test we'll drive a sinewave 0..250kHz, >10Vpp, >1..2A into reactive loads (motor coils, RFID coils).
The actual challenge is the power stage. Some experimentation with the OPA544 (inverting Amp, G=2, Rin=1k, Rfb=2k) shows bad distortion above 50kHz (see pic).
Browsing the web I ran across the PA02A, which I'm really tempted to order. On the other hand - why not try and design an power-amp, suitable as building block for later applications.
I like the concept of a fast Opamp driving a complementary darlington power stage (see PA02A datasheet, page 1, http://www.apexanalog.com/wp-content/uploads/2012/08/PA02U_S.pdf). Does anybody have suggestions concerning the power transistors? Couldn't find any complementary darlington pairs fast and powerful enough. I guess we'll have to build them from single transistors. - If we accepted 20mA running through R15, the darlingtons would have to provide the rest of the 2A output load over the whole frequency range and a gain of 100. (see screenshot from datasheet).
BTW: The amp will be mounted on a big slab of aluminum and only be running for short bursts, thus an AB-power stage is acceptable.
Has anybody tackled this type of problem before and is willing to share the results?
Looking forward to your ideas.
Thanks,
-lungfish-
I'm trying to build an arbitrary signal generator for my lab.
To make things interesting, for a first test we'll drive a sinewave 0..250kHz, >10Vpp, >1..2A into reactive loads (motor coils, RFID coils).
The actual challenge is the power stage. Some experimentation with the OPA544 (inverting Amp, G=2, Rin=1k, Rfb=2k) shows bad distortion above 50kHz (see pic).
Browsing the web I ran across the PA02A, which I'm really tempted to order. On the other hand - why not try and design an power-amp, suitable as building block for later applications.
I like the concept of a fast Opamp driving a complementary darlington power stage (see PA02A datasheet, page 1, http://www.apexanalog.com/wp-content/uploads/2012/08/PA02U_S.pdf). Does anybody have suggestions concerning the power transistors? Couldn't find any complementary darlington pairs fast and powerful enough. I guess we'll have to build them from single transistors. - If we accepted 20mA running through R15, the darlingtons would have to provide the rest of the 2A output load over the whole frequency range and a gain of 100. (see screenshot from datasheet).
BTW: The amp will be mounted on a big slab of aluminum and only be running for short bursts, thus an AB-power stage is acceptable.
Has anybody tackled this type of problem before and is willing to share the results?
Looking forward to your ideas.
Thanks,
-lungfish-
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