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SImplest way to get a negative voltage to turn a JFET off?

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K3mHtH:
Hey everyone, I have a 9V battery powered circuit for a guitar effect.
I'd like to use a JFET to mute something in the audio path, but I'm already using the 9V battery as a positive power supply for the rest of the circuit. My JFET is across my audio path as a "mute" with the Source at audio-ground, which is also power-ground for the +9V supply. So I'm wondering how I can get at least -6.0V at the JFET's gate.

I see that there are charge-pump IC's like LT1054 that can obtain a negative voltage from a positive one.. awesome. But I really don't need any current here, just enough to turn the the JFET off... is there an easier way that maybe I'm missing? Are there 1:1 transformers maybe where the primary can go across my +9V supply and the secondary winding be used in the reverse direction for a negative voltage to the JFET's gate?


MathWizard:
I think a lot of common JFET's work pretty good with drain and source flipped. But do you have any BJT's ? What's the circuit ? There might be other easy things to tie to GND or there about's, with a BJT, that would mute the output audio.

David Hess:
Biasing the source positive will also turn the JFET off, but you already assigned signal ground and the negative of the battery to ground.

A charge pump can be made with diodes and capacitors if you have a square wave source.

A photovoltaic optoisolator will produce plenty of voltage to bias a JFET off with some current left over:

https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP591B-C-F/2310604

David Hess:

--- Quote from: MathWizard on February 27, 2024, 03:28:31 am ---I think a lot of common JFET's work pretty good with drain and source flipped. But do you have any BJT's ? What's the circuit ? There might be other easy things to tie to GND or there about's, with a BJT, that would mute the output audio.
--- End quote ---

They used to make "chopper" bipolar transistors that could also be used for mute circuits, but a normal bipolar transistor can be used also.

K3mHtH:

--- Quote from: David Hess on February 27, 2024, 03:31:06 am ---
--- Quote from: MathWizard on February 27, 2024, 03:28:31 am ---I think a lot of common JFET's work pretty good with drain and source flipped. But do you have any BJT's ? What's the circuit ? There might be other easy things to tie to GND or there about's, with a BJT, that would mute the output audio.
--- End quote ---

They used to make "chopper" bipolar transistors that could also be used for mute circuits, but a normal bipolar transistor can be used also.


--- End quote ---

I'm open to using other parts to mute the circuit that might not require a negative voltage, but I need the closed resistance to be 22 ohms or less and the device can't draw much power since this is battery powered.

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