I need to connect the transformer to an 5V open-collector source as shown below, but the load must not see a larger impedance than 50Ω. The 5V source is an internal source to the driver and not available outside of it. As it stands, the seen impedance will be 5k when the bjt is off, so this will not work. I need something in between and was thinking of an emitter follower (or maybe a opamp buffer), but my simulations went a bit awry (struggling with my transformer model) so I thought I'd throw this out here in case there is an obvious solution (which there probably is) that I've missed. Any ideas are welcome.