Individual power supply smoothing or a dedicated board


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  1. #1
    Fanatical Contributor Tim's Avatar
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    Default Individual power supply smoothing or a dedicated board

    Hi,

    I have a system that powers a number of high power fans at 12v and PWM's them to control the speed.
    The fans run at 12v, the incoming voltage. All that high current fan driving makes noise on the incoming voltage supply.

    In my system I have 2 + sub boards and have the option to either supply them with 12v and smooth out the ripples on each board to get my 5v, 3.3v etc I need. Or I have a purpose built a power supply board with very good smoothing and regs that I can pull the voltages off that for each board as needed.

    Any thoughts?

    Thanks

    Tim
    Tim

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    Senior Member GAMBOA's Avatar
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    Default Re: Individual power supply smoothing or a dedicated board

    Hi Tim,

    I think a DCDC isolated converter can be useful for your application.

    It is usually more expensive but also more effective.
    Regards
    Gamboa
    PowerDCDC.jpg

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    Default Re: Individual power supply smoothing or a dedicated board

    A very cheap solution but with great filtering is the capacitor multiplier.

    A series NPN pass transistor that is bias with a relatively large resistor and a large capacitor from base to ground. The output voltage is 0,6 volts less than the input but with extremely low noise. Even lower that on the 78xx or 317 series regulators.

    Ioannis

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    Senior Member Stephen Moss's Avatar
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    Default Re: Individual power supply smoothing or a dedicated board

    It depends on the situation and what is causing the noise, is it the result of high current spikes from the PWM switching or arcing of the brushes if the fans are using a standard rather than brushless DC motors?
    Are the sub boards you mentioned the ones driving the fans or are they performing other functions?

    If the sub board are performing other functions then personally I would opt for a separate supply as I would think that should give the best isolation but if that was not practical I would try (never actually done it) splitting the 12V out from a single point to each board rather than daisy-chain them. Put filters on the input of any no fan controlling board and a largish capacitor and transzorb on the input of the fan control board to try and reduce noise from switching current spikes being transmitted back along the 12V rail.

    I recently had to redesign a simulation of an electric car drive system which was rather noisy (probably the brushes of the DC motor than the drive boards or 3-phase brushless motor). Just separating out the high (drive boards, motor and 36V, 4A supply) and low current sides (hall effect (BLDCM & current) sensors & Arduino), into separate area's of the PCB, placing nice big ground planes in both area's on both sided of the PCB and only linking the ground planes via a single 0 ohm link just to reference the Arduino ADC reading made a big difference as with high and low current sides powered separately any non radiated noise had to be transmitted down the common ground connection.

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    Fanatical Contributor Tim's Avatar
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    Default Re: Individual power supply smoothing or a dedicated board

    Thanks every one

    The fans are 12v DC Brushless. They can draw up to 2.4 amps each. As can be seen from this AN doc
    http://www.powerampdesign.net/images/AN-24_Eliminating_Circuit_Noise_From_Cooling_Fans.pdf

    You can introduce a lot of noise into the system with them.

    In my system I have a power socket/switch and then a small board with reverse voltage protection and the direct connections for the fans. The board also holds a couple of transistors to drive the PWM lines from one PWM line from the pic controlling the fans speeds.

    Currently I have the 12v from that board then going to a main board with reg and some big caps to smoothing things out. It all seems to work well. A new design will have 3-4 boards and really do not want to duplicate the caps etc on every board. Also some boards will need 2 or more voltages, again see no sense in having multiple sets of regs when perhaps I can just have 1 board that has all the smoothing and multiple power rails.

    Thanks

    Tim

    Tim

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