That is what I have been saying.Could the reference to DC be the cause of the malfunction? The opams are no longer the rc4558 but the lm4562.
I just looked for a data sheet and J112 specifies 5V max for cut off, so -5.8V should be cut off (high impedance). Have you confirmed that drain and source voltages are 0V ?The measurements are the curious thing, when negative voltage (-5.8Vdc) is applied to the gate of Q14 and Q15 they remain conducting. But if I remove one of the two (or Q14 or Q15), the one that remains in the circuit acts as a switch correctly.
A positive drive to a N channel JFET will cause the gate diode to forward bias and clamp at roughly +0.5V DCHi John,
when I measure the voltages without Q14 or Q15, at Gate they are +6.3Vdc (for driving) and -5.5Vdc (for opening the switch). In source we have a voltage that goes up and down in the order of mVolts. Then in Drain 0Vdc.
Once j112 (Q14 and Q15) are connected to the circuit, we obtain the values: Gate: +0.5Vdc /-5.5Vdc, Source: +2.5mV/-0.5mV, Drain: +2.5mV/+2.5mV.
Thanks for the attention. I've been thinking about this problem for 1 week without solving anything....
Measuring FETs can be funny, it doesn't take any current to switch states, they respond to voltage, if the gate is clearly below pinch off (-5V) the drain/source should be high impedance. Of course the drain and source also need to be proximate to 0V or higher while that is being measured.It is strange because with the voltage of -5.5Vdc I measure continuity between drain and source and I obtain about 25ohm, this in both (Q15 and Q14). Which I don't know what to try. Should I try another Jfet that is more similar to the tis75 or maybe a mosfet?
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