[sdiy] Voltage switching. Opamp, MOSFET or BJT.

[harry bissell]

Hi Thomas

The choice depends on if you need to drive the load
both low and high... 

The MOSFET and BJT will usually pull up, or pull down,
but not both (unless you use two per output).

The CMOS 4049 and 4050 buffers have the ability to
sink quite a large current, but the source is not as
good.

You could parallel CMOS gates in the same package and
get larger (and symmetrical) drive currents.

Opamps could be a good choice for higher current as
well.

You might want to scope the output of a good board and
see if it really outputs symmetric square waves... if
the waveform is different you'll want to copy it
exactly... or those notes will sound different...

H^) harry


--- Thomas Blumensath <soundgood at web.de> wrote:
> Hallo,
> 
> I am repairing this old organ and have to replace
> one chip.
> 
> 
> I will use a 4024 CMOS counter but I don't know how
> much current I have to drive into the circuit so I
> want to have same sort of switch, sitching the
> Voltage and the driving current into the circuit.
> I wonder what would be the best switch to drive my
> load. I don't know exactly how low the input
> impedance of my circuit is but there is a 2 kOhm
> resistance in parallel with it so the resistance is
> below this.
> 
> The required Voltage is 6V which is my supply line
> Voltage.
> 
> Would it better to use an OPAmp or should I use
> MOSFETs or even BJT's.
> 
> Space is also an problem cause I want to keep the
> circuit is small as possible. So are there any
> MOSFET ICs out there with say 8 MOSFET switches in
> them?
> 
> Any help and tips would be nice.
> 
> Thanks.
> 
> 
> Thoms
>
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