Stuck at amplifying output of a flip flop to drive a relay

[saurabh_m]

hi guys,
I have to drive a mechanical relay from an edge Triggered D-flip flop. output voltage from the flip flop at max when using IC 4013 is 17.27 volts at 40.6 mA. My relay coil rating is 24 volts, although i can drive it using 16 volts because minimum driving voltage is 70% of the max rated coil voltage. i have tried transistor 2N5296 but i am not able to bias it properly i guess. so basically i'm stuck. Any suggestions. thanks

 

[ericgibbs]

hi guys,
I have to drive a mechanical relay from an edge Triggered D-flip flop. output voltage from the flip flop at max when using IC 4013 is 17.27 volts at 40.6 mA. My relay coil rating is 24 volts, although i can drive it using 16 volts because minimum driving voltage is 70% of the max rated coil voltage. i have tried transistor 2N5296 but i am not able to bias it properly i guess. so basically i'm stuck. Any suggestions. thanks

hi,
What type of D flip flop is it,? 17V seems very high.

Also what is the current rating of the 24v relay

 

[saurabh_m]

Hey,
its a positive edge trigger D- flip flop, instead of a clock i'm using a momentary push button.Basically to power up the IC i am using a Battery eliminator which can regulate from 1.5 volts to 12 volts at 500 mA. By applying a max of 12 volts from the the eliminator i'm getting 17.27 volts at 40.6 mA at Q output of the flip-flop.
The coil rating is around 55 mA

 

[ericgibbs]

Hey,
its a positive edge trigger D- flip flop, instead of a clock i'm using a momentary push button.
The coil current rating is around 55 mA

hi,
The max recommended voltage for a CD4013 is 15V at which it can source or sink approx 6mA.

The gain of a 2N5296 at 100mA is approx 30.

So for a relay coil that requires 50mA at 24V the 2N5296 will be OK.

So I would suggest a transistor base resistor of approx 15V/.005 = 3.0K , say 2.7K

Connect the output of the 4013 to the 2k7 and the other end of the 2k7 to the base of the 2N5296.
Connect the emitter of the transistor to 0V and the collector to one end of the relay coil.

Connect a diode across the relay coil, to protect the transistor, cathode of the diode to +24v and the anode to the transistor collector.

Do you follow OK.

 

[saurabh_m]

Thanks a ton buddy. will try it and let u knw.

 

[saurabh_m]

hi,
it worked like a gem, although i had decrease the resistance value and make it to nearly 1.7k to drive the transistor.

 

[Hero999]

Yes, it's not surprising you needed to reduce the base resistor. Eric probably didn't notice that the gain of 30 was specified with a collector-emitter voltage of 4V so the voltage drop was probably too high.

 

[ericgibbs]

Yes, it's not surprising you needed to reduce the base resistor. Eric probably didn't notice that the gain of 30 was specified with a collector-emitter voltage of 4V so the voltage drop was probably too high.

hi,
I did notice, but as it was quoted in the datasheet for a 100mA collector current and the OP's relay required only 50mA.

Anyway, main point is we have another satisfied customer...

 

[ericgibbs]

hi,
it worked like a gem, although i had decrease the resistance value and make it to nearly 1.7k to drive the transistor.

hi,
Good news, what supply voltage are you powering the CD4013 with.??

Measure the 4013 output voltage on that pin when its driving the transistor, let me know.