Hello everyone,
I designed and built a circuit but made some mistakes during the design process and now would like to get some help before trying to fix them.
Basically I have a MCU which outputs a specified voltage with a DAC. After the DAC I wanted to have a way to switch where the output voltage goes to. Because relays are big and bulky, cost much etc, I decided to make a switch using MOSFETs. I found a schematic on the internet and designed my schematic based on it.
(I have many of these in parallel for switching.)
ADC shows where my DAC (yes, I accidentally drew ADC on the schematic) output voltage goes to. FET is P channel depletion MOSFET.
Now I see that there are 2 problems with this schematic:
1) If my DAC output voltage is low, then resistor bridge formed with 10k resistor and NPN transistor does not function
2) P channel depletion MOSFET is almost impossible to find (I was a genius an used enchancement MOSFET..)
Now I have to idea to make following changes to my schematic:
Instead of MOSFET I am thinking on using a JFET. (Have not added the bleed resistor on the schematic.)
I would need to have as small voltage drop on the FET as possible (milliOhms preferred). It needs to work when DAC output is low as 0.1V for example.
So I am open for suggestions. Maybe someone knows a good P-channel depletion MOSFET I could find (would be great if is available in SO-8). Or should I change to JFET or maybe there are other good options.
I designed and built a circuit but made some mistakes during the design process and now would like to get some help before trying to fix them.
Basically I have a MCU which outputs a specified voltage with a DAC. After the DAC I wanted to have a way to switch where the output voltage goes to. Because relays are big and bulky, cost much etc, I decided to make a switch using MOSFETs. I found a schematic on the internet and designed my schematic based on it.
(I have many of these in parallel for switching.)
ADC shows where my DAC (yes, I accidentally drew ADC on the schematic) output voltage goes to. FET is P channel depletion MOSFET.
Now I see that there are 2 problems with this schematic:
1) If my DAC output voltage is low, then resistor bridge formed with 10k resistor and NPN transistor does not function
2) P channel depletion MOSFET is almost impossible to find (I was a genius an used enchancement MOSFET..)
Now I have to idea to make following changes to my schematic:
Instead of MOSFET I am thinking on using a JFET. (Have not added the bleed resistor on the schematic.)
I would need to have as small voltage drop on the FET as possible (milliOhms preferred). It needs to work when DAC output is low as 0.1V for example.
So I am open for suggestions. Maybe someone knows a good P-channel depletion MOSFET I could find (would be great if is available in SO-8). Or should I change to JFET or maybe there are other good options.
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