#711 Basics: Power Supply (part 1 of 5)

Episode 711
Back to basics: Power Supply
AC to DC conversion, bridge rectifier
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[JayJay-kimi]

I love your videos because you explain the purpose of the chosen components and why they are there. Over time I see the same patterns in lots of circuits and I can easily spot a voltage divider and rectifier bridge.

[illuminatyinc.]

Sir, I am an electronics engineering student and I must say your videos helped me out a lot. Thank you.

[gabortorok]

Such a wonderful piece of educational content. Friendly tone with lots of insights. It inspires me to look for such things as regulators, time constants, etc. Love it, THANK YOU!

[Savan_Triveda]

Excellent teaching. Even someone who has no idea about electronics can learn something from IMSAI Guy.

[jeffdeez]

This is my 1st tutorial of yours I am watching and it is so helpful as I am a beginner electronics learner. Thank you! 🙏🏼

[sklise]

much better then my electronics 101 class. i am rusty on the math, and appreciate the breakdown!

[aerofart]

I really enjoy (and appreciate) the way you cover every detail in your videos. Thank you and Keep up the great work!

[BeetleJuice]

I built the original smart kit psu back in 1995, and never found any analysis of how it works. Thank you!

[clems]

BTW: I love these types of videos, you do a great job..

[dand]

The bridge diodes at 3A DC out will see about 4.5A RMS, with top-wave spikes above 20A; not just 3A as stated.

[jenntek.]

I have the "fake" version of this board.
I'll watch your whole series...
I have plenty of 5v and 12v fans, and fairly larger heat syncs salvaged from CPUs etc.
I just have to source a nice AC transformer for this...
As I have learned, you can not use a DC transformer.
I'm sure you mention this somewhere along the way...
:)
Dabbling in electronics, and building kits like this is great.
I wish I would have started sooner.

[argcargv]

Even at 12v, the power dissipation in the fan regulator will become problematic. A typical 12v fan will draw over 100ma which is over 2 watts, definitely will need to add a heat sink. I used a small switching buck converter module to run a 12v fan.

[henriaalderink]

Thanks for this interesting video. I am puzzled about the bleeding resistor. Is the capacitor not discharging over the diode bridge and the secondary coil of the transformer? I got triggered by the fact that the bleeding R is just generating heat during normal operation and seems to make the power supply less efficient.

[thomas-ioh]

Wow, I've seen some poorly drawn schematics before, but this one is one of the worst !!! Thank you for translating it using the proper symbols, properly !!!

[carlwedekind]

Don't forget that the resistor across the filter capacitor also serves to discharge the capacitor for safety reasons. Although not really dangerous at this voltage, a capacitor can hold a high voltage for a long time unless discharged. My linear amplifier takes almost 60 seconds to discharge the capacitors from 3700V to below 100V. de WG2E.

[clems]

Can you do a video explaining how to use balance resistors. As often seen across diodes that are in series. . The series diodes are often used to increase the voltage handling capacity. And they use resistors across those diodes to "balance" the voltages. I would love to hear how this works and how to calculate them...

[flemmingchristiansen]

Be careful if you change the 7824 regulator. There can be more than 30 V on the input: Most 7812 can not handle 30V on the input, it is 24V i think, With a 24 V transformer you get about 34V.

[nabzero]

Hi, what again is the purpose of the 3300 uF capacitor? I get how the bleeder resistor works due to the existence of the capacitor.

[gloubiboulgazeblob]

[QUESTION] in one of my PC switching power supplies, the fuse literally EXPLODES. Its replacement does only lead to another magnificent explosion, reducing the fuse to dust...

Obviously there's a short....Ok, now, what did cause this short ?

Trying to find out why, I found and/or saw 6 elements that are broken :

1) a thermistor (SKC-2R56, diameter 13mm, R=2.5 Ohms, 6A), just after the fuse, is broken (the upper part)
2) the bridge rectifier (GBU606 mounted on a heatsink) : it's dead (a test, unsoldered from the PCB, showed only 2 diodes of the bridge are ok)
3) a N-channel MOSFET (MDP13N50, mounted on the same heatsink) seems dead as well (tested off the PCB)
4) an IC has partially exploded (I can see its guts partially), and I can only see it's 2 first ID digits : "A6...". After a research, I found that it's most probably an IC of the STR-A6000 series (Off-Line PWM Controllers with Integrated Power MOSFET, the sixth pin of the normally 8 pins is absent)
5) after a test of the surface components below the PCB, I found one diode that is dead.
6) the big filter capacitor (400V, 180µF ) is dead as well : test gave me 5.5nF

I think it's not a good idea to repair it, too many broken components, but ask myself, what did cause that short-circuit in the first place ?

I suspect the bridge rectifier is the culprit of that disaster, any similar experience ?

[petermikus]

Theoritically speaking if you really wanted to use the 7805 could you hook up a 7812 in front of it you know conect the 12 output to the 7805s input would that do anything usefull would it even be a good idea?