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?