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24VAC to DC

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Yansi:
Does not depend on capacitance.

halfwave or fullwave, peak voltage is the same. Regardless if there is some or none capacitance.

mariush:

--- Quote from: joeyjoejoe on January 19, 2020, 08:50:12 pm ---
For the time-delay fuse, something like this? https://www.digikey.ca/product-detail/en/bel-fuse-inc/RST-100-BULK/507-1166-ND/809310

--- End quote ---

If you want to be more user friendly, consider fuse holders

See what sizes are most common and have the most different values in stock.
For example
* 5mm / 5.1mm / 5.2mm  x 20mm and
* 6.35mm x 22mm / 25 mm/25.4mm (0.25" x 0.875"..1" - same distance between 2 holders can be used for all three sizes, the holders are wide enough to accept 3mm of play)
seem to be plentiful and easy to buy in local shops by someone.

There's also 6.3 x 32mm (0.25" x 1.26") that's very common... and the 6.3x25 fits within the footprint of one of these ... so you can make footprints for 3 holders on circuit board but populate only 2, depending on which fuse you end up using.

example of 5mm x 20mm fuse holder (2 of these needed per board) : https://www.digikey.ca/product-detail/en/bel-fuse-inc/FC-211-22/507-1415-ND/622587

example of fuses

~530 results: 5mm or 5.1mm (metal is flexible enough to accept either) : https://www.digikey.ca/products/en/circuit-protection/fuses/139?FV=46%7C13837%2C46%7C14314%2C-8%7C139&quantity=10&ColumnSort=2088&page=1&pageSize=25

~3080 results (919 in stock) : 5.2mm x  20 mm fuses (should fit in 5mm fuse holders just fine) : https://www.digikey.ca/products/en/circuit-protection/fuses/139?k=&pkeyword=&sv=0&pv46=14397&sf=1&FV=-8%7C139&quantity=10&ColumnSort=2088&page=1&pageSize=25


6.3 / 6.35 mm fuse holder example: https://www.digikey.ca/product-detail/en/bel-fuse-inc/FC-102-22/507-1702-ND/622585

6.3 x 22-25mm fuses: https://www.digikey.ca/short/z71rr8

With bigger currents, you can make footprints on board for 6.3/6.35 x 22-25mm and an extra footprint for 6.3 x 32mm distance, so basically 3 holders but only solder 2 holders. If you happen to be "out of stock" of 6.3 x 25 you could solder holder on 6.3x32 footprint and use 6.3 x 32 fuse.

The fuse you chose may work just fine and it has the benefit of being tight package (4.35mm x 8mm) but there's no visual indication if the fuse is blown (user may not have a multimeter) while with a glass fuse user may see the wire blown ... also, user may not buy that fuse on amazon or local store instead you may force him to buy it from you or digikey or other distributor and he may be forced to pay a few dollars in shipping.
In contrast, 5x20mm fuses are easily available on amazon for example : https://www.amazon.com/s?k=fuse+5+x+20+mm&ref=nb_sb_noss_2

The bigger footprint would also allow you to put a sticker (or print on pcb) with current and speed ex "0.1A T / Slow"
(slow blow is time delay more or less)

joeyjoejoe:
 :) Good points. I am so used to designing size-constrained boards - no need to for this one. Fuse holders can be something easily sourced from China as well if needed!

joeyjoejoe:
Here's the relay driver I came up with.



These are dual mosfets (3v3 logic, 200mA continous) so I can get two to drive four relays. Relays are ~50mA. The pulldown is so we have a defined state in case anything happens to the MCU.

Paul Moir:
Presuming K1_EN is a 3.3v output from a uC, watch out:  that MOSFET has a Vgs(th) of up to 3.1volts.  The threshold means that's when it just starts to turn on.  Note that Rds(ON) is specified only down to a Vgs of 4.5 volts (3.3 ohms).  Check out the pg 3 top left graph with drain current vs Vgs.  Pretty marginal at 50mA eh?  Especially if it gets cold?  And what exactly is the voltage on K1_EN when loaded down with a LED there anyway? 
I'm pretty sure you can get a better part for less money.  Sorting by quantity in stock is a quick way of turning up the good ones.  ;)

The 10K resistor is presumably a pull down to keep the MOSFET switched off while K1_EN is booting up?  Maybe LED1 is enough depending on it's colour and the Vgs of the MOSFET you select. 

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