Re: Help. Transistor circuit that connect or disconnect 75ohm terminator for video application

Mark,

Oops!  Your right. But my schematic is wrong.  The actual circuit on
my breadboard does have the 75 ohm on the collector.  Also, I have
tried the colector to GND.   Unfortunately, the video signal does dip
to the negative and that the reason I had to pull the emitter to -5v.
Also, 75 ohm is at the drain and not at the sourcefor the FET.  I
still get the unfavorable frequency response and the wobble.  Thanks
to bring out the mistake on my schematic.

Caesar 
On 1 Feb 2006 19:22:57 -0800, "Mark" <makolber@xxxxxxxxx> wrote:

>
>LCR
>
>if the emitter is at -5 volts and the base is being pulled to 0 or +5
>then the transistor never turns off ..... no?
>
>Its not the base voltage to ground that you need to think about but the
>base voltage relative to where the emitter is, and the emiiter is at
>-5.
>
>I think you want to put the emitter at ground, and put the 75 Ohm term
>resistor in series with the collector....
>
>and you are probably better off using a FET for this as it will conduct
>current in both directions.... but also think about the GS voltage  to
>be sure you are turning the FET on and off when you want it to...
>
> imagine connecting a volt meter acorss the GS or BE junction, not from
>the Gate or base to ground...
>
>have fun
>Mark

.

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