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Thread: Compact Aux power supply for smps

  1. #1
    .... Silvio's Avatar
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    Compact Aux power supply for smps

    Here I am presenting an auxiliary power supply meant to be fitted with a SMPS of half or full bridge. The output voltage was chosen to be 17v which is quite ideal for this purpose. However this voltage can be varied to suit the particular need . The TOP221P chip is utilized as this comes in various shapes as 8 pin DIL or TO220. The chip comes also in various wattages such as 9 to 20 watts in DIL and SMD form and 12 to 150 watts in TO220 package. The chip has soft start and also short circuit protection built in.

    In my case the output of the chip is not isolated and also the input bridge and bulk capacitor has been omitted as this Aux supply is to be powered from the main bulk capacitor of the smps. The Aux is meant to be fitted on the main pcb.

    Operation
    The chip incorporates basically 3 terminals which are Drain, source and control. In the DIL format pins 1,2,3 and 6, 7, 8 being the source pins. This is meant for the chip to dissipate the heat to the copper clad of the PCB. Pin 4 is the control and pin 5 is the drain.
    With the control pin fitted directly to the output the output voltage is set to 5.6v however this can be varied with the insertion of a zener diode and also with a potential divider. In my case I used both. I used a 10v zener in series with a potential divider and a series diode to trim to the needed voltage of 17 volts. However this voltage can be varied to suit different needs by changing the zener voltage.

    The power absorbed was with a maximum of 8 watts 17v and 500mA. Idle power is 1watt
    The EE transformer details are as follows
    The centre core measurement is 5.7mm X 5.7mm Area 0.32cm^2 and outside dimensions are 20 x 20mm
    Gap is 0.15mm (0.006)
    Primary inductance 2.4mH (125 turns 0.16mm ecw) Secondary inductance is 65uH (10 turns 2X 0.4mm ecw)

    The PDF file in the bottom can be downloaded with the detailed PCB and component layout and schematic

    AUX SMPS 172.jpgAUX SMPS 173.jpgAUX SMPS 171.jpg

    smps 2k-2 aux.pdf

  2. #2
    Why not using a buck convertor for auxiliary supply? We don't need it to be isolated.

  3. #3
    .... Silvio's Avatar
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    Quote Originally Posted by expressel View Post
    Why not using a buck convertor for auxiliary supply? We don't need it to be isolated.
    It is a buck converter and the ground is not isolated

    AUX schematic.JPG

  4. #4
    I meaned that but from 320V instead


  5. #5
    .... Silvio's Avatar
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    Yes I know that this could only have an inductor but then you will need an external mosfet. Also dropping down the voltage from 320 to 15 or 20v is rather high and extra care in design should be taken. I usually see this type of buck converter in smaller amplifiers where the current is small.

  6. #6
    I will try because I have good experience with buck convertors. You are dropping many volts but its not linear, its PWM.
    Last edited by expressel; 01-28-2019 at 06:45 PM.

  7. #7
    In our local markets, this tiny 4cmx8cm board is readily available for a little over $1. It has 5V, +/-12V . Looks well made.
    Uses Viper22 or a Chinese clone IC. For that price, it is a steal - maybe rewind the transformer to get the higher voltage you want.

    https://www.aliexpress.com/item/AIYI...967418778.html

    AIYIMA-1-DVD-EVD-DVD.jpg

    AIYIMA-1-DVD-EVD-DVD.jpg
    Last edited by quadtech; 02-14-2019 at 11:41 AM.

  8. #8
    .... Silvio's Avatar
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    I bought some of these in fact and its true they are cheap. I could not bring the voltage more than 15v. I do not know the schematic of these either and I was afraid that the feedback winding supplying the IC will overload it if I had to rise up the voltage more than that. In my case the chip works off 320v directly so there is no problem about the set output voltage.

    In my aux the peak voltage of the small buck converter rises up to 32v so the output can be risen to over 20v if wanted. The power will always be 8 watts . The current rises and falls according to the output voltage so that 8w can always be drawn from it.

    The supply is meant for smps aux and this can be enhanced also to work with the power shutdown in conjunction with over current. However an NPN transistor can be added to the circuitry this will have the collector and emitter across the zener. when this transistor is switched thus shunting the zener will bring the voltage down to around 5v. This will also shuts down the oscillator chip like the SG3525 etc as these have a threshold voltage which they start or stop operating. Keeping all this in mind this auxiliary supply was built to meet these criteria.

  9. #9
    diysmps Member* res_smps's Avatar
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    dear all,
    I have tried both flyback and buck using TOP224, I got up to 450mA continuous for buck converter
    please this PI's design idea (attached)
    Attached Files Attached Files

  10. #10
    diysmps Member* res_smps's Avatar
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    my schematic
    buck1.jpgtop224-buck1.pngtop224-fly2.jpgtop224flyback.jpg
    note for buck :

    tested up to 450mA, more than that excessive heat on the chip
    1K5 resistor added to the output to prevent voltage surge
    D1 & D2 should be of an ultrafast reverse recovery type (< 50 nsecs) and rated for 1.2 * VIN(MAX) and 3*Io

    Silvio, sorry I did not mean to hijack your thread, because I'm not always online to manage my own thread.
    I think you and other member can iuse this as a reference

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