This is my first time designing a High voltage switch, as come up with some interesting thing that I want to ask about. My application needs to short out a signal line to HIGH, with a 3v3 signal from the MCU. Very little current needs to pass through to I thought well, a MOSFET will do! and designed a circuit with 2 N-FET. But the problem was that there was some voltage drop across the line which was big enough(4V for 52V supply) to keep the signal to be realized as HIGH.
This is the first circuit.
The 3V3 signal from the NPN was enough to drive a 2n7000, which got me to build the circuit and test it. But, the output from the actual circuit is when 3.3V square wave goes in, I get 4.5V when the high side voltage is 56V.
So I moved to TINA-TI for another simulation, which gave me a totally different result from PSPICE and my experiment. Here is the schematic and the sim result.
You can see that the FET doesn't even switch at all.
Now I realize that the part i have used(RK7002BM) whichis a 60A, 250mA small signal mosfet might not be getting enough Vgs for a Vds of 56. P-channel is not an option, since I need to make this work some how within a few days, and I don't have any lying around at the moment.
I have considered using relays, but all I have around are rated for 30V so no option here too.
So in conclusion the question is 1. Why would my simulation results be different between themselves and the experiment. Would it be simply due to the different parts? 2. Any help on how to get this thing working? The application, embedded layer is almost done and I really need to get this circuit done fast.
Thank you for baring with such a long question.
Thank you for the comments. I don't know what I was thinking when I wrote this, I was overwhelmed by the fact that I am still working on a Sunday 4pm from Monday, never got a chance to get home....
To clarify, I am trying to build a high voltage, low-side FET switch.
The high voltage is the 50V/56V, that I wish to toggle on/off. I was trying to achieve it through drain of the FET. However, OptoFETs like this seems to do the job. I have tried with PowerFETs, but the resistor got burnt.
This is the circuit with IRF830
I am kinda clueless to what is going on......