How I can switch or route -75V & +5V to set of PIN diodes as required

[rajan_pec]

PROJECT DESCRIPTION:

There are 6 different channels or filters ( based on frequency ) to route the RF signal. Each channel or filter is made up of a circuit containing a set of PIN diodes.

To switch on to the particular channel or filter (let say channel-1)PIN diodes of that channel(ch-1)needs to be switch ON (by providing +5V) & simultaneously other channels(ch-2 to ch-6) needs to be switch OFF (by providing -75v to all respective PIN diodes).

To implement this process we are considering MOSFETs as a switch, to switch ON or OFF the channels which is shown in the figure or attachment.

In the initial testing we have powered the gates of IRF6216PBF MOSFETs by using external power supplies instead of controlling through microcontroller.

Gate ,powered with 0V, results in +5.0V at the Drain pin (R33) of the respective MOSFET and gate, powered with +5V, results in -75.0V at the Drain pin (R33) of the respective MOSFET.

PROBLEM:

when using microcontroller (MCU) we are not getting same result as by using external supplies. Using a MCU, MOSFET takes more time to switch from ON to OFF state (in seconds) secondly, all MOSFETs are not behaving equally. Sometimes MOSFET switches to ON state some times it doesnot.

so we are thinking that ,some additional circuitry is required to drive the gate of MOSFET.

So plz suggest simple circuit which may help in building my project.


Regards,




Rajan

 

[BradtheRad]

Do all gates have a definite voltage being sent to them?

Or, do you switch them so the gate is disconnected? A floating gate can pick up stray signals and mains hum out of the air.

Furthermore, is each gate definitely referenced to the device controlling the mosfet?

Advice is to connect a 10k resistor from the gate to the source terminal. The source is the more negative pin of an Nmos. The source is the more positive pin of a Pmos.

 

[rajan_pec]

"Do all gates have a definite voltage being sent to them?"--->> Yes, 0V (low) to provide +5.0V at the Drain terminal of MOSFET & +5.0V (high) to provide -75V at the drain terminal of the MOSFET

" do you switch them so the gate is disconnected?"-->>Switching of each gate terminal is done through MCU
"pick up" can be the reason

"is each gate definitely referenced to the device controlling the mosfet?"---> Yes

I will implement your advice , 10K resistor, and inform u back.

Regards,
Rajan

 

[BradtheRad]

1.

The IRF6216PBF is a P-device. Its positive supply needs to be connected to the same supply which controls the gate. It will not turn off reliably otherwise.

2.

There is a hazard when you apply greater than +/- 40V across a mosfet's gate-to-drain or gate-to-source.

 

[mtwieg]

That circuit is going to be very slow, and dissipate a lot of excess power when in the forward bias state.

I've used the driver circuit presented in **broken link removed** (figure D.1) many times and it works well, and can be driven by a 5V MCU just fine. It is designed to have forward-bias current limiting built into it (set by the value of R3), rather than outputting a fixed 5V, which is usually what a good driver circuit does. It should be plausible to replace T1 with a P channel FET.