How to replace relay with transistor

Other Hardware General Electronics
1

hello friends,

i am doing a project in it i need to use two realys.need to switch 5v and the load is a 3.7v battery for one relay ,and another load is a gas sensor for next relay .it make my pcb bulky.. i need to reduce the product size... so any one can say how to replace a relay with transistor...thank you very much....

2

What is the maximum current you need to switch for each?

3

thanks for your reply "strykeroz"....here i attached my circuit for your kind perusal

ckt.jpg
ckt.jpg1836×3264 939 KB

4

How does the booster enjoy having 5V at the input?

5

strykeroz:
How does the booster enjoy having 5V at the input?

More to the point, how does the battery like having 5 V connected directly? You should be using a proper charging circuit. You could then leave the 3.7 to 5 V converter permanently connected to the sensor/controller and no need for relays at all.

Russell.

6

russellz:
More to the point, how does the battery like having 5 V connected directly? You should be using a proper charging circuit. You could then leave the 3.7 to 5 V converter permanently connected to the sensor/controller and no need for relays at all.

Russell.

hello sir.. thanks for your reply,i forgot to mention that there is charging ckt TP4056 between adapter and the battery..but i do not understand completely you said.. you think if i use a charging ckt then no need of any relays and always take power from the battery not directly from the adapter so no need of switching ,,,isnt it sir?...

7

ecworks:
you think if i use a charging ckt then no need of any relays and always take power from the battery not directly from the adapter so no need of switching ,,,isnt it sir?...

Quite.

Russell.

8

russellz:
Quite.

Russell.

ok no problem