transistor AND-ing switch

Thread Starter

masa6614

Joined Nov 9, 2008
48
Hi,
Attached is a drawing of what i'm wondering will work. I'd like to make a AND gate to control a switching transistor to close and open a relay. Now my Vcc is too high and i dont want to scale it down in size and provide the smaller supply power for a real logic AND gate to control a transistor. I'm not sure if the first transistor, 'Q1' needs a highside driver or if it will work fine the way it is? Thanks

( and sorry i realize i put it in the wrong forum and cant figure out how to move or delete it from here )
 

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kubeek

Joined Sep 20, 2005
5,795
If you provide both with vcc and most importantly keep the zeners, then it should work. Cmos NAND gate uses the same topology for the AND part I think.
But anyway, what voltage are you talking about? I don´t think this is suitable for high voltage. And also some gate resistors wouldn´t hurt, without them the zener might burn, or oscillation can occur.
 

Thread Starter

masa6614

Joined Nov 9, 2008
48
Okay, thanks, yeah the Vcc is 24V, but what i didnt show in the diagram was the signals are opamp outputs with a series 10k to get the gate voltages to ~12V and limit the zener current.
 

kubeek

Joined Sep 20, 2005
5,795
If you don´t require fast switching, then it should be ok. What voltage are the zeners? I would use 15V for mosfets with 20V Vgsmax.
 
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