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Put the transistor back and change to R =50 to 500 Ohms depending on LED string current.

We want to ensure base current = >5% of LED current. Preferably 10%. (never use Vgs(th)2~4V FETS on 3.3V logic. It needs >5V.) All IRFxxx's I think are this way, Now they make Logic level FETS with a different prefix in P/N.

Your design was (3.3V-0.6Vbe)/5k=Ib= 540 uA.

Change Rb to >= 100 Ohms and it will work off any 3.3V logic and NPN open collector. Iout=(3.3-Vbe)/(Rcmos+Rs)= (3.3-0.7)/(33+100)=20 mA so it can drive 200mA to 350mA on collector with low Vce(sat)

Adjust series Rs as required.

^{simulate this circuit – Schematic created using CircuitLab}

When you see a Vgs(th) for a FET. You will need at least 2 to 3x Vgs(th) (threshold) conduct fully.

Change to R = 500 Ohms or less depending on LED string current such that input current is 5~10% of switched output current.

IRFxxx FETs are Vgs(th)=3V +/-1 tolerance This is the threshold for 500uA not Amps !!

So you need >4.5V for Vgs or this IRFxxx family of FETs and preferably 10V for rated RdsOn as shown in specs.

You ONLY get 10% of hFE = Beta as a saturated switch.

We want to ensure base current = >5% of LED current. Preferably 10%. (never use Vgs(th)2~4V FETS on 3.3V logic. It needs >5V.) All IRFxxx's I think are this way, Now they make Logic level FETS with a different prefix in P/N.

Your design was (3.3V-0.6Vbe)/5k=Ib= 540 uA.

Change Rb to >= 100 Ohms and it will work off any 3.3V logic and NPN open collector. Iout=(3.3-Vbe)/(Rcmos+Rs)= (3.3-0.7)/(33+100)=20 mA so it can drive 200mA to 350mA on collector with low Vce(sat)

Adjust series Rs as required.

^{simulate this circuit – Schematic created using CircuitLab}

Put the transistor back and change to R =50 to 500 Ohms depending on LED string current.

We want to ensure base current = >5% of LED current. Preferably 10%. (never use Vgs(th)2~4V FETS on 3.3V logic. It needs >5V.) All IRFxxx's I think are this way, Now they make Logic level FETS with a different prefix in P/N.

Your design was (3.3V-0.6Vbe)/5k=Ib= 540 uA.

Change Rb to >= 100 Ohms and it will work off any 3.3V logic and NPN open collector. Iout=(3.3-Vbe)/(Rcmos+Rs)= (3.3-0.7)/(33+100)=20 mA so it can drive 200mA to 350mA on collector with low Vce(sat)

Adjust series Rs as required.

Put the transistor back and change to R =50 to 500 Ohms depending on LED string current.

We want to ensure base current = >5% of LED current. Preferably 10%. (never use Vgs(th)2~4V FETS on 3.3V logic. It needs >5V.) All IRFxxx's I think are this way, Now they make Logic level FETS with a different prefix in P/N.

Your design was (3.3V-0.6Vbe)/5k=Ib= 540 uA.

Change Rb to >= 100 Ohms and it will work off any 3.3V logic and NPN open collector. Iout=(3.3-Vbe)/(Rcmos+Rs)= (3.3-0.7)/(33+100)=20 mA so it can drive 200mA to 350mA on collector with low Vce(sat)

Adjust series Rs as required.

^{simulate this circuit – Schematic created using CircuitLab}

Put the transistor back and change R =50 to 500 Ohms

We want to ensure base current = >5% of LED current. Preferably 10%. (never use Vgs(th)2~4V FETS on 3.3V logic. It needs >5V.) All IRFxxx's I think are this way, Now they make Logic level FETS with a different prefix in P/N.

Your design was (3.3V-0.6Vbe)/5k=Ib= 540 uA.

Change Rb to >= 100 Ohms and it will work off any 3.3V logic and NPN open collector. Iout=(3.3-Vbe)/(Rcmos+Rs)= (3.3-0.7)/(33+100)=20 mA so it can drive 200mA to 350mA on collector with low Vce(sat)

Adjust series Rs as required.

Put the transistor back and change to R =50 to 500 Ohms depending on LED string current.

We want to ensure base current = >5% of LED current. Preferably 10%. (never use Vgs(th)2~4V FETS on 3.3V logic. It needs >5V.) All IRFxxx's I think are this way, Now they make Logic level FETS with a different prefix in P/N.

Your design was (3.3V-0.6Vbe)/5k=Ib= 540 uA.

Change Rb to >= 100 Ohms and it will work off any 3.3V logic and NPN open collector. Iout=(3.3-Vbe)/(Rcmos+Rs)= (3.3-0.7)/(33+100)=20 mA so it can drive 200mA to 350mA on collector with low Vce(sat)

Adjust series Rs as required.