Power Supply Design 2 - the Fuse and thermistor
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- Опубликовано: 7 июл 2024
- Continuing with the power supply design guide; power cord to DC output. This video covers the fuse and thermistor selection.
Power Supply Design #8 How Much Power? • Power Supply Design #8...
Power Supply Design #7 Capacitor - How Big? • Power Supply Design #7...
Power Supply Design #6 Capacitor • Power Supply Design #6...
Power Supply Design #5 Full Wave Rectifier • Power Supply Design #5...
Power Supply Design #4 diode rectifiers • Power Supply Design #4...
Power Supply Design #3 the Toroidal Transformer • Power Supply Design #3...
Power Supply Design 2 - the Fuse and thermistor • Power Supply Design 2 ...
Power Supply Design 1 - the Power Cord • Power Supply Design 1 ... 
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I love this attention to detail ! (Though you could speed it up a tad, you know...)
Tho' a plain desktop power-supply is a bit unworthy of your attentions, sir, because most times the job will get done anyway.
Not to say that design sloppiness is OK, but the applications will usually condone it. However, I have a suggestion :
Please take up a more critical gadgets such as 1) UPS 2) DC Welding-Inverter 3) AC TIG Welding Inverter
wherein your attention to detail will make a difference of working or dead gadget, which is satisfying !
As I said before, we would end up with useful gadgets as well as an education this way.
I like that idea - thank you for this input!!
@@KissAnalog i think your speed is fine
Old vid but good material. I missed the relationship between Fuse & Thermistor preceding Filter Caps. Thanks for posting.
Great stuff again thanks!
Thanks Adam - I appreciate you!
Eddie...I am lovin' your power supply series!
That's great Steve! I'll have plenty more. I have an SMPS design (AC/DC for audio amps) that I want to do very soon.
Nice info, thanks :)
You bet! Thanks for the feedback!
If I’m running 220v ac to use a thermistor do you need to hook only 1 thermistor to one side of the hot line? Or do you need to hook to one to each hot line being 220v? It’s hard to find any info on this topic.
Great question! No, it is still a series circuit, but the current will be higher with the higher voltage so the thermistor needs to be rated for that current. Thanks for asking.
Great and clear info! What if we used a 1,000V 1A in a circuit using 1.5V 1.5A, would the fuse still blow?
I mean, there are a lot difference in power between 1,000W and 2.25W.
Yes you are right there is a lot of difference in the power, but fuses melt with current heating and then blow open - finally opening the circuit when the gap is big enough to quinch the arc. As long as the fuse is rated for enough voltage - then it should be good. Higher voltage could result in more force opening the fuse, but then the arc might last longer too. It would be interesting to test an extreme case that you present;) I should do a short video on a fuse I invented;) I will do a video on how you can make a fuse from wire and/or trace on a Pcb.
I was wondering replacing a slow blow fuse for two fast blow in parallel not sure the formula for this, would it be half the current rating of the slow blow for each fast blow fuse?
I wouldn't recommend using 2 fuses in parallel. They will not share perfectly and then you have to compensate by making them larger current ratings, and then you lose protection. Try using a fast blow at the next higher current rating, or at the same current rating and see if it isn't slow enough;) Even fast blow fuses are slow...
Very interesting video, thanks. Looking at subsequent videos where you deal with inrush current, it’s obvious that the thermistor is providing quite some protection - IIRC, it drops the current from around 68A to 12A. I assume that the rating of the fuse you would use is based on that value? More generically, having calculated the thermistor to use and its operating characteristic, you determine an appropriate fuse? I further assume that the downstream current that the load can draw also plays a part - does the thermistor play a limiting role across the whole circuit in terms of current that can be supplied (I may have confused myself totally here!!)? I liked the way you went through the data sheets - I find them really hard - and it would be useful to have some worked examples for choosing the fuse and thermistor in relation to the power supply characteristics being designed for, including taking account of tolerances (for example, that thermistor you chose has a tolerance of +/- 20% so you’re somewhere between 8Ohms and 12Ohms.). Really informative video, thanks
Thank you for watching and for the great suggestions! You are right on point. I’m working on the follow up videos now and should post later today and tomorrow.
do these NTC fail over time or should they last forever unless damaged by the power?
Great question! I do think the NTC, if not overly stressed, should last very long without any issue. They are used in many power supplies without issue.
@@KissAnalog the reason I ask is my dac PSU is tick tick ticking and I hear its because a cap that charges it failed... but I'm a total noob so just checking things. Any ideas on that? It's not ticking now that's gone but the unit still won't power on
Capacitors are a common failure point. Any cap that shows any bulging should obviously be replaced. If aluminium electrolytic capacitors were used in the signal path, then these should be swapped out with poly caps.
@@KissAnalog thanks
Pen and Paper
Thanks for the feedback! ;)