[SOLVED] Basic MOSFET switch design

[skywalker898]

Hi, I would like to use a use the +5V digital output of an arduino to control a MOSFET switch, that simply has a +20V DC power supply attached to the drain in series with a 2k ohm load; the source is grounded. I have never used a MOSFET as a switch, so I am wondering if the circuit diagram I have uploaded will work **broken link removed**, and what parameters on a MOSFET datasheet I should be concerned about to make sure this works. If the circuit will work, does anyone know of any standard MOSFETs that I could use to build this?

Thanks,
Brandon

 

[goldsmith]

Dear Brandon
Hi
If your command signal is 5 volt , you can use the mosfets that called logic level series . but i suggest you to increase it's voltage with a simple ICL7667 , and then give it to uyour usual mosfet ( with 15 volt will be on ) . and another advantage of my suggestion is that , if your frequency , is a bit high , your mosfet will need some currents for gate capacitor , thus ICL7667 can support it simply , because of totem pole out put .
Best Wishes
Goldsmith

---------- Post added at 23:32 ---------- Previous post was at 23:31 ----------

BTW : you'd better to use a 47 k ohms resistor in parallel with GS junction.

 

[skywalker898]

Thanks goldsmith. I have a couple questions. For the 47k resistor at the GS junction, I believe this is used to drain any charge from the MOSFET after it is turned off. Is there any reason in particular you said a 47k resistor, or will just about any resistor work?

Also, I am confused about what voltage is necessary to saturate a given MOSFET. In general, how much higher than Vgs does the voltage need to be in order to saturate (fully turn on) a MOSFET? For example, I am looking at the logic level MOSFET FDP7030BL with a typical Vgs of 1.9V. Would the 5V output from my arduino fully turn on this MOSFET? See link for MOSFET: https://www.newark.com/fairchild-semiconductor/fdp7030bl/n-channel-mosfet-30v-60a-to-220/dp/38C7149?Ntt=FDP7030BL

Thanks,
Brandon

 

[goldsmith]

Again Hi
At first , about the reason of that resistor :
As we know , when the GS junction capacitor charged , the impedance of gate is infinite ( approx) , thus it can't become discharge ! and it will be dangerous . that resistor can discharge it . and it's value is depends on the value of Ciss and your time .
and you can test this behavior . take a mosfet , and give a voltage across it's GS junction and then , you'll see , it's DS is turn on , and if you remove that voltage , you'll see still DS is on ! but if you touch it , it will turn off ! test it , please , it will be lovely effect that you can use it on your projects!
And about saturation , i think this name is wrong ( in opposition to the BJT ) , you can say , it is on , simply !
And the reason of +15 volt for usual mosfets or +5 volts for logic level mosfets :
As we know , if you , give the voltage more than threshold voltage , your mosfet will start conduction . but not totally ! it means if you don't get it +15 for usual mosfets or +5 for logic level mosfets , your mosfet will be at linear region , and it means dissipation ! and heating ! and i don't think , that you like it !
Good luck
Goldsmith