• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need help with using a transistor or triac as a switch

MAJ

New Member
Hello everyone,

I have a digital programmable timer with signal output of 1.2V DC. It runs on rechargeable battery of 1.2V. I need to use this small output to run a small 6V relay. To my general knowledge, I need at least 3 volts to trigger a small transistor. Is there a transistor that can be triggered by 1.2V signal? or can I use a photoisolator triac to drive the relay with the small 1.2V signal? Thanks.
 

AnalogKid

Well-Known Member
Most Helpful Member
What is the current required by the relay for activation? Or, manufacturer and part number? Can you post a datasheet?

ak
 

audioguru

Well-Known Member
Most Helpful Member
The input of a transistor needs at least 0.7V with a current of at least 6mA for it to turn on your 60mA relay coil.
Can your timer produce this voltage and current? Please post the datasheet of your timer.
 

alec_t

Well-Known Member
Most Helpful Member
1.2V is plenty to turn on almost any bipolar transistor to act as a switch but, from the relay datasheet, a minimum of 4.5V is needed to operate the 6V relay. Do you have a 4.5V (or higher) supply as well as the 1.2V cell?
 

MAJ

New Member
Yes, I have a 6V DC supply board that I can fit inside the timer box, so that it powers the relay, and (after stepping down the voltage) charge the rechargeable 1.2V battery.
 

alec_t

Well-Known Member
Most Helpful Member
Providing your timer can source about 6mA a circuit like this should be able to operate the relay.
RelayDriver.png
 

crutschow

Well-Known Member
Most Helpful Member
If the timer can't source 6mA, you can add a PNP transistor gain stage (below) to reduce the required input current to about 0.6mA.

120484
 

audioguru

Well-Known Member
Most Helpful Member
What is the timer that can have a load and an output at its supply rail of 1.2V when the battery powering it is only 1.2V?
Most electronic circuits have a voltage drop when driving a load.

An old Ni-Cad cell or modern Ni-MH cell is 1.2V when half discharged. Then the transistor might not work when the battery drops to 1V.
 

alec_t

Well-Known Member
Most Helpful Member
Glad you got it working.
 

EE World Online Articles

Loading

 
Top