How to decrease 24volts op-amp output convert to TTL input level?

hi guys! if you have idea on this, my problem is i need to input the ouput voltage of my op-amp lm339 with a supply voltage of 25 volts and to NAND GATE IC LS7430..BUT THIS IC NEED ONLY A TTL inout voltage level..

LM339 is a open collector. Just put a 4.7K pull-up resister to out put of LM339 and connect other end of resister to +5v and get out from out put pin of LM339

if output of OP-amp is 25V you can use a voltage divider also then use a series resistance say 2k2 and a zener of 5.1V for safety purpose.

my above solution is just for LM339 only

[Topic moved to Electronics forum]

ah ok..got it! thank you so much for the reply guys!! =D

hi! this circuit i attached is having a problem in the part of voltage comparator, i tested the 12v zener,with a voltage level of 11.8 and the voltage divider in the input and it is working, my lm393 comparator is working, here's the problem, when i input a 24.7 Vin the comparator triggers the 2n3904 transistor after that the when i'm decreasing the voltage input Vin to 22volts, the lm393 is still triggering the 2n3904 base which should not be. the purpose of the circuit is to power up the device using 24 volts input. please advise. thanks in advance.

well it will trigger it anyway.. coz if your input voltage changes... it will change at both the places i mean at inverting and non-inverting end. and inverting will always be more than your non inverting input.

take this example...
if input is 24V, at U3 Pin 2 will have 24v and Pin 3 will have 12V which will trigger your transistor.. now if you change your vcc to 22v then at Pin2 it will 22 and pin 3 will be 11 and again the same case. I hope you're getting my point.

hi! this circuit i attached is having a problem in the part of voltage comparator, i tested the 12v zener,with a voltage level of 11.8 and the voltage divider in the input and it is working, my lm393 comparator is working, here's the problem, when i input a 24.7 Vin the comparator triggers the 2n3904 transistor after that the when i'm decreasing the voltage input Vin to 22volts, the lm393 is still triggering the 2n3904 base which should not be. the purpose of the circuit is to power up the device using 24 volts input. please advise.

80proof

Can you measure for the voltages at the following points at 24.7 ,22 volts and 18 volts.


LM393 pins 2,3 and output.
The base and collector of the 2N3904.

Where it says micro controller ground, is it actually connected to anything ?
If so try disconnecting it.

@ 24.7v pin2 is 11.95v and pin3 is 12,@ 22v pin2 is 11.92v and pin3 is 10.67,@ 18v pin2 11.86 and pin3 is 8.74, the purposed of 2n3904 is designed to give GND on MCu. do you have any suggestion in my circuit for just switching the GND to MCU GND?? or is there any better and cheaper component for switching?? thanks in advance.