Need help with using a transistor or triac as a switch

[MAJ]

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.

 

[Nigel Goodwin]

Your general knowledge is wrong, it takes about 0.7V to turn a silicon transistor ON.

 

[AnalogKid]

What is the current required by the relay for activation? Or, manufacturer and part number? Can you post a datasheet?

ak

 

[MAJ]

Your general knowledge is wrong, it takes about 0.7V to turn a silicon transistor ON.

And? where is your help?

 

[MAJ]

What is the current required by the relay for activation? Or, manufacturer and part number? Can you post a datasheet?

ak

Hello AK, Attached is the datasheet. The model is SRD-06VDC-SL-C.

 

[Nigel Goodwin]

And? where is your help?

How much more help do you need?, your original premise was incorrect - just use a bipolar transistor, as with any small relay driver.

 

[audioguru]

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]

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]

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]

Providing your timer can source about 6mA a circuit like this should be able to operate the relay.

 

[crutschow]

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.

 

[audioguru]

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.

 

[Nigel Goodwin]

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.

Presumably it's an FET switch, so no voltage drop as such.

 

[MAJ]

Hello Elec_t,
your circuit worked like a charm with the 1.2V signal. Many thanks.

Providing your timer can source about 6mA a circuit like this should be able to operate the relay.
View attachment 120481

 

[MAJ]

Thanks everyone.

 

[alec_t]

Glad you got it working.