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Make a 5V out trigger a 3V in

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panfilero

Member
Hello,

I'm trying to find out, what's the best way to get a logic device that outputs 5V to trigger something that requires 2.8V. Here's my thing:

I'm using an OR gate (74HC32) to trigger an analog switch that requires 2.8V to switch. My switching speeds will be very low (50Hz max). My switch draws little current (maybe 5mA), which the OR gate can source.

I'm thinking I need some kind of transistor set-up here, but I'm not sure what to I need to go with... mosfet? bjt? emitter-follower? pnp? pull-up, pull-down...

if anyone could point me in the right direction I would very much appreciate it.

much thanks!
 

MikeMl

Well-Known Member
Most Helpful Member
Post a link to the data sheet for your analog switch.
 

MikeMl

Well-Known Member
Most Helpful Member
Since the control voltage can go from 0 to Vcc, why not run the entire circuit including the CMOS on 4.7V?

If you really must run the switch on a lower voltage than the CMOS, then a simple interface like this one will work:
 

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audioguru

Well-Known Member
Most Helpful Member
Why not use two resistors to divide the 5V pulses down to 2.8V pulses?
 

panfilero

Member
Thanks for the circuit idea MikeMI, I'm not sure how it works, but it looks really simple and clean, I'm gonna study it for a minute.... I don't drop it all down to 4.7V because there's other chips and logic before my OR-Gate that need the 5V, and I'm trying to run as close to the recommended values as possible for the switch (I'm new at this so maybe it's overkill on my part to try and hit the recommended values... I dunno)

audioguru, I tend to stay away from votlage dividers here because the output voltage would change with the voltage across the divider, and this circuit will be driven by a 9V battery, so as my battery drains it might affect the output of the divider.. but maybe not, I'll look into it some more, thanks for the suggestion
 

audioguru

Well-Known Member
Most Helpful Member
The max allowed supply voltage for the 74HC132 is 6V so it needs a low-dropout 5V regulator if you are using a 9V battery.
The analog switch should also be powered from the 5V regulator. Then you do not need level conversion.
 

panfilero

Member
I do have a 5V regulator powering my OR gate, but I'm not using 5V for the switch because to the switch datasheet the min and max recommended operating conditions are

Vcc 2.7V-4.3V
Vcntrl 0-Vcc

5V is outside of their recommended operating conditions.
 

audioguru

Well-Known Member
Most Helpful Member
The max supply voltage for the switch IC is 6.0V and the max control voltage is its power supply voltage. Its recommended max voltages are 4.3V.

then power the 74HC32 and the switch from 4.7V or less.
 
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