+ Post New Thread
Results 1 to 18 of 18
  1. #1
    Newbie level 3
    Points: 429, Level: 4

    Join Date
    Oct 2010
    Posts
    4
    Helped
    0 / 0
    Points
    429
    Level
    4

    Relay control circuit

    I need to control a simple relay with a push button; push on/push off. I found this circuit online which seems simple enough except it's for +6-19 VDC. I need to run it with 24-28VDC. It's been a very long time since my basic electronics and semi-conductors training in the Navy. What, if anything, do I need to do to this circuit to use %30 higher operating voltage? Assuming the coil in K1 is a 24 volt coil, can I just raise the value of R3 and R6 to say, 5.6 K or would I need to do more?

  2. #2
    Advanced Member level 5
    Points: 13,738, Level: 28
    nandhu015's Avatar
    Join Date
    Feb 2006
    Location
    India
    Posts
    1,961
    Helped
    299 / 299
    Points
    13,738
    Level
    28
    Blog Entries
    18

    Re: Relay control circuit

    Use a positive voltage regulator, For example 7812.


    1 members found this post helpful.

  3. #3
    Newbie level 3
    Points: 441, Level: 4

    Join Date
    Jul 2010
    Location
    Tunis
    Posts
    3
    Helped
    0 / 0
    Points
    441
    Level
    4

    Re: Relay control circuit

    Use a positive voltage regulator, For example 7812.
    why?

    I need to control a simple relay with a push button; push on/push off. I found this circuit online which seems simple enough except it's for +6-19 VDC. I need to run it with 24-28VDC. It's been a very long time since my basic electronics and semi-conductors training in the Navy. What, if anything, do I need to do to this circuit to use %30 higher operating voltage? Assuming the coil in K1 is a 24 volt coil, can I just raise the value of R3 and R6 to say, 5.6 K or would I need to do more?
    I think you can feed your circuit without changing the values of R3 and R6



    •   AltAdvertisment

        
       

  4. #4
    Advanced Member level 3
    Points: 4,912, Level: 16
    Achievements:
    7 years registered
    KJ6EAD's Avatar
    Join Date
    Oct 2010
    Location
    Earth
    Posts
    709
    Helped
    196 / 196
    Points
    4,912
    Level
    16

    Re: Relay control circuit

    Just run it. The transistors can handle 40 volts and 1 amp. In this circuit, to switch the transistors, it's more about the relative voltages than absolute voltages. I think the numbers were originally for a 6 or 12 volt relay coil.
    Last edited by KJ6EAD; 21st October 2010 at 18:13. Reason: Add note about current.



  5. #5
    Newbie level 3
    Points: 441, Level: 4

    Join Date
    Jul 2010
    Location
    Tunis
    Posts
    3
    Helped
    0 / 0
    Points
    441
    Level
    4

    Re: Relay control circuit

    vce only 30V
    Last edited by keith1200rs; 22nd October 2010 at 04:39. Reason: Signature violation



  6. #6
    Advanced Member level 3
    Points: 4,912, Level: 16
    Achievements:
    7 years registered
    KJ6EAD's Avatar
    Join Date
    Oct 2010
    Location
    Earth
    Posts
    709
    Helped
    196 / 196
    Points
    4,912
    Level
    16

    Re: Relay control circuit

    I must have been looking at the datasheet for the new and improved model.



    •   AltAdvertisment

        
       

  7. #7
    Newbie level 3
    Points: 429, Level: 4

    Join Date
    Oct 2010
    Posts
    4
    Helped
    0 / 0
    Points
    429
    Level
    4

    Re: Relay control circuit

    Quote Originally Posted by KJ6EAD View Post
    Just run it. The transistors can handle 40 volts and 1 amp. In this circuit, to switch the transistors, it's more about the relative voltages than absolute voltages. I think the numbers were originally for a 6 or 12 volt relay coil.
    I see what you're saying about the relative versus absolute voltage. So if I do build it and run it as is with a 24-28V source, the circuit will work with a 24V relay coil that draws maybe 50ma?



  8. #8
    Advanced Member level 3
    Points: 4,912, Level: 16
    Achievements:
    7 years registered
    KJ6EAD's Avatar
    Join Date
    Oct 2010
    Location
    Earth
    Posts
    709
    Helped
    196 / 196
    Points
    4,912
    Level
    16

    Re: Relay control circuit

    Yes. The transistor that's driving the relay coil can handle it easily.



    •   AltAdvertisment

        
       

  9. #9
    Newbie level 3
    Points: 429, Level: 4

    Join Date
    Oct 2010
    Posts
    4
    Helped
    0 / 0
    Points
    429
    Level
    4

    Re: Relay control circuit

    Okay so I built this thing up last night and tried it at 12 and 24 volts and nothing worked. So I went back over everything this morning and all is correct. I started checking voltages in various places and found that all three transistors appear to be partially conducting all the time. I even disconnected the base on Q3 to get it to stop conducting and nothing changed. Once I adjust the source voltage up to about 14-15 volts, the relay energizes regardless of what the rest of the circuit is doing. So I'm thinking I have a shorted transistor or something. I pulled another one out of the bag and looked at it more closely. It said 2N2907 on it. I looked that up on Google and found it to be a PNP transistor, the complement transistor for the 2N2222 which of course, is NPN. The package says they are suppose to be NPN switching transistors but guess what? They aren't. That will teach me not to buy parts from Radio Shack. So I am thinking that once I get the correct transistors in there it should work.



  10. #10
    Advanced Member level 1
    Points: 4,606, Level: 16
    Achievements:
    7 years registered

    Join Date
    Jan 2006
    Location
    Singapore
    Posts
    425
    Helped
    45 / 45
    Points
    4,606
    Level
    16

    Re: Relay control circuit

    Some reference to interface the digital logic signal to control a relay.
    Switch



  11. #11
    Member level 3
    Points: 1,397, Level: 8
    mehtadhaval's Avatar
    Join Date
    Sep 2010
    Posts
    56
    Helped
    7 / 7
    Points
    1,397
    Level
    8

    Re: Relay control circuit

    This circuit should work....

    Click image for larger version. 

Name:	IRreceiver.GIF 
Views:	20 
Size:	6.5 KB 
ID:	50161

    It uses a digital counter and the last bit of the output is used to drive the relay through 2n2222 transistor. But be careful, when using 40 v. Because I think the 7805 voltage regulator is not able to withstand 40 volts i/p. So either u have to lower the operating voltage (around 30v). Or u have to find some other means to generate 5v from 40v.



  12. #12
    Member level 4
    Points: 939, Level: 6
    sam185's Avatar
    Join Date
    Aug 2009
    Location
    India
    Posts
    72
    Helped
    18 / 18
    Points
    939
    Level
    6

    Re: Relay control circuit

    first you need to select appropriate relay ,transistor rating for that & I think the pulse-width is based on r1,r2 and c what ever value you calc for r3,r6:- r3=r6 for proper output. That's all.
    Last edited by sam185; 23rd October 2010 at 09:42.



  13. #13
    Full Member level 2
    Points: 2,872, Level: 12
    Achievements:
    7 years registered

    Join Date
    Aug 2007
    Location
    Indonesia
    Posts
    125
    Helped
    13 / 13
    Points
    2,872
    Level
    12

    Re: Relay control circuit

    I suggest you use ULN2001-ULN2003, with common GND. It's effective and easy.



  14. #14
    Newbie level 3
    Points: 429, Level: 4

    Join Date
    Oct 2010
    Posts
    4
    Helped
    0 / 0
    Points
    429
    Level
    4

    Re: Relay control circuit

    Okay so once I got the correct transistors installed (the package was labeled wrong) the circuit works okay except that it seems to require a second or two between button pushes to change state. If I push the button to quickly, it does nothing untill I give it a second or two and then push the button again. I don't expect the circuit to be operated all that quickly when it's in operation but you never know. Is there something in the circuit that can be changed to eliminate this required two second pause? Decrease the size of R2 or C1 perhaps?



    •   AltAdvertisment

        
       

  15. #15
    Super Moderator
    Points: 49,672, Level: 54
    Achievements:
    7 years registered
    keith1200rs's Avatar
    Join Date
    Oct 2009
    Location
    Yorkshire, UK
    Posts
    10,877
    Helped
    2075 / 2075
    Points
    49,672
    Level
    54

    Re: Relay control circuit

    Yes, reduce C1.

    Keith



  16. #16
    Member level 4
    Points: 939, Level: 6
    sam185's Avatar
    Join Date
    Aug 2009
    Location
    India
    Posts
    72
    Helped
    18 / 18
    Points
    939
    Level
    6

    Re: Relay control circuit

    You can reduce either c1 or r2, but if you reduce r2 that will be more better.



  17. #17
    Super Moderator
    Points: 49,672, Level: 54
    Achievements:
    7 years registered
    keith1200rs's Avatar
    Join Date
    Oct 2009
    Location
    Yorkshire, UK
    Posts
    10,877
    Helped
    2075 / 2075
    Points
    49,672
    Level
    54

    Re: Relay control circuit

    I suggested C1 because if you reduce R2 too much then there is a risk of upsetting the collector voltage on Q1 which is in turn the base voltage for Q2. There isn't that risk in reducing C1.

    Keith.



  18. #18
    Member level 4
    Points: 939, Level: 6
    sam185's Avatar
    Join Date
    Aug 2009
    Location
    India
    Posts
    72
    Helped
    18 / 18
    Points
    939
    Level
    6

    Re: Relay control circuit

    Yes you are right keith. i have not seen that part.



--[[ ]]--