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  • Confirmation needed

    From Phil Allison@21:1/5 to [email protected] on Sun Aug 29 17:48:23 2021
    [email protected] wrote:
    =======================

    I'm going to make a 12v DC power supply with a linear reg. I will
    half-wave rectify 12v AC and have a smoothing cap. The load is only 10ma.

    So: 12v RMS is 17v peak, minus the diode drop of 0.7 is 16.3v peak.
    Using a 47uF cap, the ripple will be 3.5v p-p. So the min voltage into
    the regulator will be 16.3-3.5 = 12.8. Ripple calculated from Vpp =
    i/fC (.010/(60*47e-6).


    ** Yep two:

    1. The drop out voltage of a standard 12v reg IC is not 12.8 - more like 13.8.
    2. The AC supply varies and may be be 10% low on occasion.


    So, you need a 15VAC tranny.

    OR you can make a "voltage doubler" supply with two diodes and two electros.

    That will give about 33V DC - minus the same deductions.




    ..... Phil

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  • From Bob Engelhardt@21:1/5 to All on Sun Aug 29 20:15:49 2021
    I'm going to make a 12v DC power supply with a linear reg. I will
    half-wave rectify 12v AC and have a smoothing cap. The load is only 10ma.

    So: 12v RMS is 17v peak, minus the diode drop of 0.7 is 16.3v peak.
    Using a 47uF cap, the ripple will be 3.5v p-p. So the min voltage into
    the regulator will be 16.3-3.5 = 12.8. Ripple calculated from Vpp =
    i/fC (.010/(60*47e-6).

    Am I missing anything?

    Thanks, Bob

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  • From Bob Engelhardt@21:1/5 to Phil Allison on Sun Aug 29 22:41:27 2021
    On 8/29/2021 8:48 PM, Phil Allison wrote:
    [email protected] wrote:
    =======================

    I'm going to make a 12v DC power supply with a linear reg. I will
    half-wave rectify 12v AC and have a smoothing cap. The load is only 10ma.

    So: 12v RMS is 17v peak, minus the diode drop of 0.7 is 16.3v peak.
    Using a 47uF cap, the ripple will be 3.5v p-p. So the min voltage into
    the regulator will be 16.3-3.5 = 12.8. Ripple calculated from Vpp =
    i/fC (.010/(60*47e-6).


    ** Yep two:

    1. The drop out voltage of a standard 12v reg IC is not 12.8 - more like 13.8.
    2. The AC supply varies and may be be 10% low on occasion.


    So, you need a 15VAC tranny.

    OR you can make a "voltage doubler" supply with two diodes and two electros.

    That will give about 33V DC - minus the same deductions.




    ..... Phil


    Thank you - that is helpful in 2 ways: pointing out what I missed &
    was wrong about, and even more helpful is not having to correct my analysis.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to [email protected] on Sun Aug 29 23:31:10 2021
    [email protected] wrote:

    ** Yep two:

    1. The drop out voltage of a standard 12v reg IC is not 12.8 - more like 13.8.
    2. The AC supply varies and may be be 10% low on occasion.

    So, you need a 15VAC tranny.

    OR you can make a "voltage doubler" supply with two diodes and two electros.

    That will give about 33V DC - minus the same deductions.


    Thank you - that is helpful in 2 ways: pointing out what I missed &
    was wrong about, and even more helpful is not having to correct my analysis.

    ** If your 12v tranny is really small, like say 100mA - it will output about 15V to 16v AC off load.

    So would do at a pinch with a puny 10mA DC load .


    ....... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bob Engelhardt@21:1/5 to Phil Allison on Mon Aug 30 14:55:18 2021
    On 8/30/2021 2:31 AM, Phil Allison wrote:
    [email protected] wrote:

    ** Yep two:

    1. The drop out voltage of a standard 12v reg IC is not 12.8 - more like 13.8.
    2. The AC supply varies and may be be 10% low on occasion.

    So, you need a 15VAC tranny.

    OR you can make a "voltage doubler" supply with two diodes and two electros.

    That will give about 33V DC - minus the same deductions.


    Thank you - that is helpful in 2 ways: pointing out what I missed &
    was wrong about, and even more helpful is not having to correct my analysis.

    ** If your 12v tranny is really small, like say 100mA - it will output about 15V to 16v AC off load.

    So would do at a pinch with a puny 10mA DC load .


    ....... Phil





    Thanks again - I will take some measurements on the tranny.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bob Engelhardt@21:1/5 to Bob Engelhardt on Tue Aug 31 20:08:16 2021
    On 8/30/2021 2:55 PM, Bob Engelhardt wrote:
    On 8/30/2021 2:31 AM, Phil Allison wrote:
    [email protected] wrote:

    ** Yep two:

    1. The drop out voltage of a standard 12v reg IC is not 12.8 - more
    like 13.8.
    2. The AC supply varies and may be be 10% low on occasion.

    So, you need a 15VAC tranny.

    OR you can make a "voltage doubler" supply with two diodes and two
    electros.

    That will give about 33V DC - minus the same deductions.


    Thank you - that is helpful in 2 ways: pointing out what I missed &
    was wrong about, and even more helpful is not having to correct my
    analysis.

    **   If your 12v tranny is really small, like say 100mA  -  it will
    output about 15V to 16v  AC off load.

          So would do at a pinch with a puny 10mA DC load .


    .......  Phil





     Thanks again - I will take some measurements on the tranny.

    Thanks again - that's good to know. The OC voltage is 15v & it doesn't
    drop below 12v until loaded to 200ma. That gives me a lot of working room!

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