Switching a fet from a pic

[hamopp]

Hi
If i supply 12v for 741 will that work ok ?

Regards
Hamopp

 

[audioguru]

Hi
If i supply 12v for 741 will that work ok?

Maybe.
The 44 years old 741 opamp was designed to use ONLY a 30V supply. Its datasheet does not show what happens with a lower voltage. Some might work with only 12V.
Why not use a modern opamp that is guaranteed to work with a 12V supply?
Then you can tell your teacher where to go.

 

[crutschow]

Hi
Here is a circuit that i found on the net that use mmbf170 fets to switch audio from
the detectors to the audio amp.

The gates are fed from a pic (direct).

How can this be ?, When the bs170\mmbf170 has a VGSS Gate-Source Voltage ± 20 V.
you will need about at least 10 volts on the MOSFET gate to turn it fully on?

If you don't need the minimum ON resistance from the transistor, such as for a high impedance audio circuit, 5V Vgs may be sufficient to turn on the MOSFET sufficiently for the circuit requirements. For example Figure 2 in the Fairchild data sheet for the bs170\mmbf170 shows a nominal ON resistance of about 1.5 times minimum at Vgs = 5V at low currents which gives a 7.5 ohm maximum ON resistance. This is low compared to most audio circuit impedances.

 

[hamopp]

Why not use a modern opamp that is guaranteed to work with a 12V supply?
Then you can tell your teacher where to go.

I'am my teacher lol

 

[audioguru]

Why does a teacher use a 44 years old opamp???
GROW UP!

 

[hamopp]

HA HA
That was the part that was used in the mute circuit from 2002

Can you suggest an opamp to use in that circuit ?

 

[audioguru]

There are thousands of modern opamps that work much better than a 741 opamp.

 

[hamopp]

Hi
Will a TL081 FET opamp do ?

Regards
Hamopp

 

[audioguru]

The minimum supply voltage for a TL081 opamp is 7V.

 

[hamopp]

Hi
Was gonna use it at 12v