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).
bobenge...@gmail.com 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
** 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.
bobenge...@gmail.com 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
On 8/30/2021 2:31 AM, Phil Allison wrote:
bobenge...@gmail.com wrote:Thanks again - I will take some measurements on the tranny.
** 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
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