switching small 5vdc load with 110vac

[Mike]

I need to switch a very small 5vDC load with a 110vAC trigger. I wish to
keep my solution simple, and small. The 5vDC load is actually the button
contacts on a PC joystick. With my limited electronics experience, I would
typically use a transformer to get the 110vac down to something usable (like
12vdc). Then, I would use a 12vdc relay. While this is simple, it is not
small. Is there a single component solution, or even an IC that could do
this?? I was looking for a small (less than 1" cubed) 110vac relay but
could find nothing (my local dealer said that there isn't really an
application where 110vac is used to switch something that small, therefore
most 110vac relays will be larger to handle a larger load).
Any suggestions appreciated.
-Mike

 

[Jimmy]

Use an opto isolator. connect the LED to 110 AC through the appropriate
droping resistor and connect the transistor output across the contacts. A
light bulb and a photo transistor may work better.

 

[nemo]

I need to switch a very small 5vDC load with a 110vAC trigger. I wish to
keep my solution simple, and small. The 5vDC load is actually the button
contacts on a PC joystick. With my limited electronics experience, I would
typically use a transformer to get the 110vac down to something usable (like
12vdc). Then, I would use a 12vdc relay. While this is simple, it is not
small. Is there a single component solution, or even an IC that could do
this?? I was looking for a small (less than 1" cubed) 110vac relay but
could find nothing (my local dealer said that there isn't really an
application where 110vac is used to switch something that small, therefore
most 110vac relays will be larger to handle a larger load).
Any suggestions appreciated.
-Mike

You could use low voltage, sub-minature printed-circuit mounting relay with
a diode across the coil (they're DC) and driven by 110V through a suitable
resistor to drop the Voltage. You could easily fit all this on a 1" square
piece of Veroboard.

You'll need a bit of maths to work out the value and get the Wattage right
otherwise the resistor will get hot.

For example: using a 12V relay, measure the resistance of the relay coil and
use a resistor ten times that value. Work out the current flowing, multiply
this by the Voltage drop across the resistor, add a bit for luck and that
will give you the Wattage of the resistor you need.

A 1N4001 diode will do across the coil.

If the relay buzzes a bit, bung a 47 or a 100micro-farad electrolytic
capacitor across the coil too. Observe the polarity though or it'll go bang!

Try http://rswww.com/

They stock a good range - of everything.

Nemo

 

[Robert]

I might be completely wrong here, very possible, but I would have
thought the use of a fly-back converter, or even just a buck converter
would be perfect. I am pretty sure there are buck ICs out there that
need the resistors and caps added to your specifications, and should
easily fit on a 1" square PCB. Maybe this isn't what you are looking
for but its just an idea I would have thought of to do your job. But
don't listen to me I don't know that much as most of you are probably
thinking right about now.

Rob

 

[Robert]

I am back again I just found a product at ON Semiconductor go here if
you want to look, I think it would do what you require. Maybe you can
rip the idea has all the design layout and stuff so see what you
think!

http://www.onsemi.com/pub/Collateral/AND8099-D.PDF

Rob

 

[nemo]

Is that some sort of Switched Mode device? A bit of a technological overkill
over a resistor, a diode and a capacitor surely?

("Oy!! Don't call me Shurely!!")

)

 

[Mike Scott]

Did you read this PDF? Yikes! This is way beyond my electronics
experience. All I'm hoping to find is a miniature device that is a relay
(or acts like a relay) with my specified input (110vac). Even though your
response is OVER my head, I do appreciate the input -thanks!
-Mike

 

[Robert]

No worries mate, yeah its similar to stuff I learnt at uni thats why i
mentioned it. Our lecturer made us learn heaps about Swith Mode
Regulators.

Hope you get something working.

Rob

 

[Form@C]

I need to switch a very small 5vDC load with a 110vAC trigger. I wish to
keep my solution simple, and small. The 5vDC load is actually the button
contacts on a PC joystick. With my limited electronics experience, I
would typically use a transformer to get the 110vac down to something
usable (like 12vdc). Then, I would use a 12vdc relay. While this is
simple, it is not small. Is there a single component solution, or even an
IC that could do this?? I was looking for a small (less than 1" cubed)
110vac relay but could find nothing (my local dealer said that there isn't
really an application where 110vac is used to switch something that small,
therefore most 110vac relays will be larger to handle a larger load). Any
suggestions appreciated.
-Mike

Not a single-component solution AFAIK. I could get it down to 2 though...
An AC opto-isolator (i.e. one with 2 leds in it) fed from the 110v line
via a capacitor to limit the LED current. You can calculate the value of
the capacitor! Look up the formula for capacitive reactance and use your
normally calculated LED dropper resistance to find the value of capacitor
needed. This has the advantage over a resistor of not needing to dissipate
a lot of heat.

Go on then - here's the formula:

Xc= 1
--------
2 PI F C

.... and here is the rearrangement to find C:

C= 1
---------
2 PI F Xc

Note: Xc is in ohms and C is in Farads

Try running the opto-isolator input at about 2-3mA.

It might be a good idea to shunt the capacitor with a high value resistor
(say 470k) to discharge it when the supply is switched off.

If you can't find an AC opto-isolator use an ordinary dc one with a diode
(1N4001 is ok) connected in reverse-parallel with the input.

You may have a problem with any opto-isolator system though. The output
from the transistor will be in the form of pulses while the input is on.
Unless you include software filtering, or the PC input is sluggish enough,
these may look like a *very* fast joystick! The ac opto-isolator will
produce a pulse on each half-cycle whereas a dc one will produce a pulse
on each cycle. You stand more chance of success using the AC version.


BE CAREFUL! YOU WILL BE WORKING WITH VOLTAGES THAT COULD INJURE YOU!

---and don't let the 110v into the joystick port!

 

[JeffM]

I need to switch a very small 5vDC load with a 110vAC trigger.

Not a single-component solution AFAIK.
Form@C

Years ago, Teledyne Solid State (solid state relays)
made a 76C* line of 110Vac/220Vac input, ~40Vdc output DIP SSRs.
AltaVista & Lycos didn't spot them. (Google won't take wildcards.)

It appears all SSR companies are run by idiots who want to make
finding the product you need / comparative shopping a nightmare.
Almost everybody's Selection Guide is a PDF.

The only SSR page I could find that wasn't done by a moron was:
http://www.hbcontrols.com/Relay Selection Guide.htm
(smallest 110Vac input unit is 5 amps out--BIG).

If you want to weed thru PDFs and crap:
http://www.google.com/search?num=10...+-DIP-switches+-DIP-switch&btnG=Google+Search

I think somebody makes a tiny SSR that will do what you want
(you might start at Digi-Key),
but everybody seems to be enamored with Adobe documents. (I'm not.)

 

[Tank]

Try a Crydom IAC-5 , $8.00 from Digikey.com

Years ago, Teledyne Solid State (solid state relays)
made a 76C* line of 110Vac/220Vac input, ~40Vdc output DIP SSRs.
AltaVista & Lycos didn't spot them. (Google won't take wildcards.)

It appears all SSR companies are run by idiots who want to make
finding the product you need / comparative shopping a nightmare.
Almost everybody's Selection Guide is a PDF.

The only SSR page I could find that wasn't done by a moron was:
http://www.hbcontrols.com/Relay Selection Guide.htm
(smallest 110Vac input unit is 5 amps out--BIG).

If you want to weed thru PDFs and crap:
http://www.google.com/search?num=10...+-DIP-switches+-DIP-switch&btnG=Google+Search

I think somebody makes a tiny SSR that will do what you want
(you might start at Digi-Key),
but everybody seems to be enamored with Adobe documents. (I'm not.)