[Moved]: Problem with 74ls148, voltage dropping below 5

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darkkey

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i am having a circuit that uses 74LS148 IC, input to the ic's are npn transistors and the circuit is powered by a transformer and a 7805 rectifier is in place. i have a problem, when i check the voltage in the circuit its around 2.5 to 3v. But if any one of the transistor (any one ) is turned on, then the voltage touches 5 and circuit starts working fine.

The ground and vcc to the ic is correct.

also what are the pins iam supposed to tie to ground ? i have E1 pin grounded ? Should i ground like GS or anyother ?

what might be wrong in my circuit ?..

I am having pull up resistors between transitor output and input to The encoder
 

I think you should include a bleeder resistor at 7805 output to draw some constant current. This will help regulator function as desired.
 

Oops sorry. its the other way around.. Emitter to ground collector to Ic input. and their is 10k pull up betweem collector and ic
 



Power comes from 7805.

Input to base of transistor is from some sensors and other things
 

Your schematic shows that your 74LS148 has no +5V supply on pin 16 and has no ground on pin 8. All the pullup resistors also must be connected to +5V.
 

betwixt said:
Probably wants /GS grounding too.....

Brian.
Click to expand...

Well i thought it is an output pin ?? should i ground it ?

- - - Updated - - -

Audioguru said:
Your schematic shows that your 74LS148 has no +5V supply on pin 16 and has no ground on pin 8. All the pullup resistors also must be connected to +5V.
Click to expand...

Brother, my circuit designer software hid them.. and i have mentioned in my post that ground and vcc are connected properly. also the 10k pull ups are connected to +5v itself
 

What's driving the base of your transistors? Don't just tell us "some sensors and other things". What kind of "other things"? Coat hangers? Eggplants?
 

I simulated your circuit and it does work. I use 3 push buttons with a 10K resistor to represent your sensor.

Since this is a priority encoder. Only the highest number would be shown at the outputs. For example, if I press all 3 buttons at the same time the o/p would indicate '011' ie '3'.

I suspect your sensors are not giving enough bias to the transistors to make them conduct.

Allen
 

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