Amplifying current without changing voltage

StefanZe

Joined Nov 6, 2019
191
The LM311 is a comperator not an opamp.
You can use other opamps to give you your ciruit more current capabilities. The opamp selection depends on the load you want do drive.
 

Thread Starter

zleepy

Joined Mar 1, 2023
5
Thank you for the clarification! Didnt know that i was using a comparator.
Can i get some advise with respect to the issue i am currently facing? Currently using a port expander PCF8574 as a output and doesnt seem to have sufficient current to drive my 5V relay HRS1H-S-DC5V. So if i were to use the L2722 under the voltage follower configuration, is this a feasible solution
 

StefanZe

Joined Nov 6, 2019
191
Thank you for the clarification! Didnt know that i was using a comparator.
Can i get some advise with respect to the issue i am currently facing? Currently using a port expander PCF8574 as a output and doesnt seem to have sufficient current to drive my 5V relay HRS1H-S-DC5V. So if i were to use the L2722 under the voltage follower configuration, is this a feasible solution
You won't need a voltage follower for this application. Use a transistor to to switch the coil of the relay (don't forget the freewheeling diode). You can use the port expander to drive the transistor. I would use a small n-mosfet, but a npn transistor will work too.

1677668887705.png
 

StefanZe

Joined Nov 6, 2019
191
If you use the BC337 in the circuit i posted, remove R2 and calculate the proper value for R1.
The saturation voltage Vce of the BC337 is between 0,5 and 1V depending on the collector current. If the problem in your design was the voltage drop, the saturation voltage could be a problem in the design i posted. Easiest way to solve this problem is to use a npn with a lower Vce sat or use a n-Mosfet.
 

Ian0

Joined Aug 7, 2020
10,037
The PCF8574 will sink 50mA but it can only source 4mA, so it will work without any buffer if you connect the coil between the output and 5V (but don’t forget the diode across the coil, or you’ll need a new PCF8574 the first time it switches off)
 

Thread Starter

zleepy

Joined Mar 1, 2023
5
Just tried post 5 configuration and it works! Thanks alot!! missed the diagram out previously, my internet did load the diagram out.
 
Top