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100MHz voltage controlled current sink


I am trying to build a voltage controlled current sink which can sink a current up to 300mA from DC to 100MHz. In my first draft i used one OpAmp in combination with an npn transistor to achieve the required current amplification. A Resistor 5Ohm (10R || 10R) between emitter and ground is used to build the negative feedback to close the loop. (see picture, C_in = 0pF)

There are two problems:     

  • transistor power disapation is to high (FZT651)
  • bandwidth only 10MHz (FZT651: ft = 150MHz; OpAmp: GBP = 600MHz)

Whats the matter for such a low bandwidth?

Any ideas for reducing power disapation?


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