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Simple switch circuit for 5v dc fan?

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  • Dave C
    In a small home video system it gets pretty hot. Regardless how critical this is (and how ôrobustö these are supposed to be) IÆd like to add a tiny (50 mm?)
    Message 1 of 11 , Jun 25, 2014
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      In a small home video system it gets pretty hot. Regardless how critical this is (and how “robust” these are supposed to be) I’d like to add a tiny (50 mm?) 5v fan I have.

      I want to turn this on and off at some threshold temperature (empirically determined), probably by adjusting a pot. Sense would be— what, a thermistor?

      I’ve searched but it seems that the microcontroller has taken over this task completely. I do see some stand-alone pwm circuits but I’m looking for maybe a transistor and a few resistors or even a small PC-mount relay?

      Supply is 5v so I know the fan will have to run on something less that due to loss in the switch if I go with transistor solution.

      2-wire fan draws 72 ma at 5v.

      Ideas?

      Thanks,
      Dave
    • John Popelish
      On 06/26/2014 02:07 AM, Dave C davec2468@yahoo.com ... At 72mA, the switch losses would be very small, maybe 0.1 volt. I would probably go with a low voltage
      Message 2 of 11 , Jun 25, 2014
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        On 06/26/2014 02:07 AM, Dave C davec2468@...
        [Electronics_101] wrote:
        > In a small home video system it gets pretty hot.
        > Regardless how critical this is (and how “robust” these
        > are supposed to be) I’d like to add a tiny (50 mm?) 5v
        > fan I have.
        >
        > I want to turn this on and off at some threshold
        > temperature (empirically determined), probably by
        > adjusting a pot. Sense would be— what, a thermistor?
        >
        > I’ve searched but it seems that the microcontroller has
        > taken over this task completely. I do see some
        > stand-alone pwm circuits but I’m looking for maybe a
        > transistor and a few resistors or even a small PC-mount
        > relay?
        >
        > Supply is 5v so I know the fan will have to run on
        > something less that due to loss in the switch if I go
        > with transistor solution.
        >
        > 2-wire fan draws 72 ma at 5v.

        At 72mA, the switch losses would be very small, maybe 0.1 volt.

        I would probably go with a low voltage opamp and a switching
        transistor, like a 2N3904 or a small mosfet like a 2N7000.
        A pair of resistors (or a potentiometer) set the temperature
        setpoint (as a fraction of the 5 volt supply, with a
        thermistor and a fixed resistor measuring the temperature.
        An opamp is a high gain amplifier that amplifies the
        difference between two voltages. It compares the setpoint
        voltage with the measured temperature voltage and switches
        the transistor on or off.

        Add a little positive feedback, to provide for clean switching.


        --
        Regards,

        John Popelish
      • Stefan Trethan
        I have a fan control circuit that works very well in several pieces of equipment: Sorry about the
        Message 3 of 11 , Jun 25, 2014
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          I have a fan control circuit that works very well in several pieces of
          equipment:
          <http://tinypic.com/view.php?pic=2nss26a&s=6#.U6vAeSgqinE>

          Sorry about the picture quality, I can't find a better one at the moment.
          Obviously you will already have stable voltages in the home video
          system, so you do not need the left half of the schematic.

          R1 is adjusted so that the fan just starts to turn at the temperature
          you want to hold.
          R2 provides some negative feedback to prevent oscillations.
          The mosfet is not critical, but may need to be bolted to a heatsink
          for large fans.
          The NTC resistor can be 10k, and is mounted in the airstream or to the
          heatsink you want to hold constant.


          This is a linear speed controller, the fan goes faster as the
          temperature increases.
          Much preferable to an on/off controller because of reduced noise and
          thermal cycle stress.

          ST




          On Thu, Jun 26, 2014 at 8:07 AM, Dave C davec2468@...
          [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
          > In a small home video system it gets pretty hot. Regardless how critical this is (and how “robust” these are supposed to be) I’d like to add a tiny (50 mm?) 5v fan I have.
          >
          > I want to turn this on and off at some threshold temperature (empirically determined), probably by adjusting a pot. Sense would be— what, a thermistor?
          >
          > I’ve searched but it seems that the microcontroller has taken over this task completely. I do see some stand-alone pwm circuits but I’m looking for maybe a transistor and a few resistors or even a small PC-mount relay?
          >
          > Supply is 5v so I know the fan will have to run on something less that due to loss in the switch if I go with transistor solution.
          >
          > 2-wire fan draws 72 ma at 5v.
          >
          > Ideas?
          >
          > Thanks,
          > Dave
          >
          >
          >
          >
          >
          > ------------------------------------
          >
          > ------------------------------------
          >
          > Please trim excess when replying
          > ------------------------------------
          >
          > Yahoo Groups Links
          >
          >
          >
        • Frank Mead
          here is a temperature control circuit you might find useful http://electronics-diy.com/electronic_schematic.php?id=1036 good luck, Frank On Thu, Jun 26, 2014
          Message 4 of 11 , Jun 26, 2014
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            here is a temperature control circuit you might find useful
            good luck, Frank


            On Thu, Jun 26, 2014 at 1:53 AM, Stefan Trethan stefan_trethan@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
             

            I have a fan control circuit that works very well in several pieces of
            equipment:
            <http://tinypic.com/view.php?pic=2nss26a&s=6#.U6vAeSgqinE>

            Sorry about the picture quality, I can't find a better one at the moment.
            Obviously you will already have stable voltages in the home video
            system, so you do not need the left half of the schematic.

            R1 is adjusted so that the fan just starts to turn at the temperature
            you want to hold.
            R2 provides some negative feedback to prevent oscillations.
            The mosfet is not critical, but may need to be bolted to a heatsink
            for large fans.
            The NTC resistor can be 10k, and is mounted in the airstream or to the
            heatsink you want to hold constant.

            This is a linear speed controller, the fan goes faster as the
            temperature increases.
            Much preferable to an on/off controller because of reduced noise and
            thermal cycle stress.

            ST



            On Thu, Jun 26, 2014 at 8:07 AM, Dave C davec2468@...
            [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
            > In a small home video system it gets pretty hot. Regardless how critical this is (and how “robust” these are supposed to be) I’d like to add a tiny (50 mm?) 5v fan I have.
            >
            > I want to turn this on and off at some threshold temperature (empirically determined), probably by adjusting a pot. Sense would be— what, a thermistor?
            >
            > I’ve searched but it seems that the microcontroller has taken over this task completely. I do see some stand-alone pwm circuits but I’m looking for maybe a transistor and a few resistors or even a small PC-mount relay?
            >
            > Supply is 5v so I know the fan will have to run on something less that due to loss in the switch if I go with transistor solution.
            >
            > 2-wire fan draws 72 ma at 5v.
            >
            > Ideas?
            >
            > Thanks,
            > Dave
            >
            >
            >
            >
            >
            > ------------------------------------
            >
            > ------------------------------------
            >
            > Please trim excess when replying
            > ------------------------------------
            >
            > Yahoo Groups Links
            >
            >
            >


          • Jong Kung
            These 2 circuits are working similar theory of operation - use the them sensor as resistor to form a voltage divider. Feed that to a transistor to control the
            Message 5 of 11 , Jun 26, 2014
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              These 2 circuits are working similar theory of operation - use the them sensor as resistor to form a voltage divider. Feed that to a transistor to control the current to the motor.  Then there's additional features (like feedback, led, etc.)

              That's as close to I can figure it. 

              I like ST's circuit since it is so simple. 

              =====

              This is a linear / analog circuit. The transistor will get warm / hot. That is dissipating power. Not very good idea for battery operated control. 


              Jong 



              On Jun 26, 2014, at 2:41 AM, "Frank Mead wa6ujj@... [Electronics_101]" <Electronics_101@yahoogroups.com> wrote:

              here is a temperature control circuit you might find useful
              good luck, Frank


              On Thu, Jun 26, 2014 at 1:53 AM, Stefan Trethan stefan_trethan@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
               

              I have a fan control circuit that works very well in several pieces of
              equipment:
              <http://tinypic.com/view.php?pic=2nss26a&s=6#.U6vAeSgqinE>

            • Stefan Trethan
              Yes, it s the same circuit. I just used a mosfet because I had many on hand with the isolated plastic tab (wanted to bolt it to a heatsink). Also the high gain
              Message 6 of 11 , Jun 26, 2014
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                Yes, it's the same circuit.

                I just used a mosfet because I had many on hand with the isolated plastic tab (wanted to bolt it to a heatsink).
                Also the high gain of the mosfet means you can get away with just one transistor.

                ST



                On Thu, Jun 26, 2014 at 3:28 PM, Jong Kung jongkung01@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:




                These 2 circuits are working similar theory of operation - use the them sensor as resistor to form a voltage divider. Feed that to a transistor to control the current to the motor.  Then there's additional features (like feedback, led, etc.)

                That's as close to I can figure it. 

                I like ST's circuit since it is so simple. 

                =====

                This is a linear / analog circuit. The transistor will get warm / hot. That is dissipating power. Not very good idea for battery operated control. 


                Jong 



                On Jun 26, 2014, at 2:41 AM, "Frank Mead wa6ujj@... [Electronics_101]" <Electronics_101@yahoogroups.com> wrote:

                here is a temperature control circuit you might find useful
                good luck, Frank


                On Thu, Jun 26, 2014 at 1:53 AM, Stefan Trethan stefan_trethan@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
                 

                I have a fan control circuit that works very well in several pieces of
                equipment:
                <http://tinypic.com/view.php?pic=2nss26a&s=6#.U6vAeSgqinE>




              • Jong Kung
                YESSSSSSSS !!!!!! I guessed it right !!!! Jong
                Message 7 of 11 , Jun 26, 2014
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                  YESSSSSSSS !!!!!!

                  I guessed it right !!!!


                  Jong

                  On Jun 26, 2014, at 3:52 AM, "Stefan Trethan stefan_trethan@... [Electronics_101]" <Electronics_101@yahoogroups.com> wrote:

                  > Yes, it's the same circuit.
                • Jong Kung
                  Does the R2 prevent oscillation or more linear current flow ramp (gradual turn on) to the fan ? (Just trying to learn and understand the circuit) Jong
                  Message 8 of 11 , Jun 26, 2014
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                    Does the R2 prevent oscillation or more linear current flow ramp (gradual turn on) to the fan ?

                    (Just trying to learn and understand the circuit)


                    Jong


                    On Jun 25, 2014, at 8:53 PM, "Stefan Trethan stefan_trethan@... [Electronics_101]" <Electronics_101@yahoogroups.com> wrote:

                    > I have a fan control circuit that works very well in several pieces of
                    > equipment:
                    > <http://tinypic.com/view.php?pic=2nss26a&s=6#.U6vAeSgqinE>
                    > ....
                    > R1 is adjusted so that the fan just starts to turn at the temperature
                    > you want to hold.
                    > R2 provides some negative feedback to prevent oscillations.
                  • alienrelics
                    I was going to suggest a TTL 555 timer (like the NE or SE555) as a one-chip solution, but I rather prefer the linear ramp up of speed with temperature in
                    Message 9 of 11 , Jun 27, 2014
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                      I was going to suggest a TTL 555 timer (like the NE or SE555) as a one-chip solution, but I rather prefer the linear ramp up of speed with temperature in Stefan's circuit.

                      Although I'm sure I could rig up a 555 timer as a PWM fan speed controller with a thermistor, and get linear speed with temperature with less heat/power loss.

                      But at that point, you might as well use one of the 8 pin microcontrollers. There is information on how to transfer an Arduino program onto one of the 8 pin Atmel ATtiny45 or ATtiny85 chips. Using the internal clock (4MHz) and an external transistor switch, an analog input, and analogWrite, which is about a 490Hz PWM output, you get a one chip, one transistor solution. An external potentiometer or a few buttons (one pin with several series resistors), so you can adjust the setpoints and speed.

                      The person who made a video and write-up about doing this calls it "shrinkifying" your Arduino. He gives credit to MIT Media Lab's High-Low Tech Group.

                      How-To: Shrinkify Your Arduino Projects

                       







                      Arduino Shield Makes 8-Pin Chip Programming a Snap

                       



                      Steve Greenfield AE7HD
                    • alienrelics
                      Probably both. As the voltage to the gate rises, the voltage on the drain drops, so R2 tends to pull the gate lower. So if you look at a graph of temperature
                      Message 10 of 11 , Jun 27, 2014
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                        Probably both. As the voltage to the gate rises, the voltage on the drain drops, so R2 tends to pull the gate lower. So if you look at a graph of temperature vs fan speed, the fan should speed up more gradually with temperature.

                        This is negative feedback to linearize the amplification properties of the MOSFET.

                        Steve Greenfield AE7HD


                        ---In Electronics_101@yahoogroups.com, <jongkung01@...> wrote :

                        Does the R2 prevent oscillation or more linear current flow ramp (gradual turn on) to the fan ?

                        (Just trying to learn and understand the circuit)


                        Jong


                        On Jun 25, 2014, at 8:53 PM, "Stefan Trethan stefan_trethan@... [Electronics_101]" <Electronics_101@yahoogroups.com> wrote:

                        > I have a fan control circuit that works very well in several pieces of
                        > equipment:
                        > <http://tinypic.com/view.php?pic=2nss26a&s=6#.U6vAeSgqinE>
                        > ....
                        > R1 is adjusted so that the fan just starts to turn at the temperature
                        > you want to hold.
                        > R2 provides some negative feedback to prevent oscillations.
                      • Stefan Trethan
                        That sounds a lot better than the fan oscillated, so I stuck another resistor in . Thank you. ST On Fri, Jun 27, 2014 at 6:10 PM, alienrelics@yahoo.com
                        Message 11 of 11 , Jun 27, 2014
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                          That sounds a lot better than "the fan oscillated, so I stuck another resistor in".
                          Thank you.

                          ST

                          On Fri, Jun 27, 2014 at 6:10 PM, alienrelics@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:


                          Probably both. As the voltage to the gate rises, the voltage on the drain drops, so R2 tends to pull the gate lower. So if you look at a graph of temperature vs fan speed, the fan should speed up more gradually with temperature.

                          This is negative feedback to linearize the amplification properties of the MOSFET.

                          Steve Greenfield AE7HD

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