Low Cost PS for 12 Volts, 250ma for a small DC motor

[Fred]

Hi All,

I'm looking for a means to inexpensively implement subject PS from a
240/120 mains supply without using a switch. Yep, I know that a SMPS
would do the job but can the job be done at less cost?

What I've looked at so far:

1) Capacitive Transformer. It looks like it might work except that I end
up needing large 22uF high voltage caps on the front end which are
expensive. Needs a switch.
2) Zener supply. Way too much power dissipated in the resistors. Needs a
switch.
3) CT transformer. Looks good but needs a switch.

Any bright ideas or is SMPS the solution??

Regards,

Fred

 

[Joerg]

Hello Fred,

I'm looking for a means to inexpensively implement subject PS from a
240/120 mains supply without using a switch. Yep, I know that a SMPS
would do the job but can the job be done at less cost?

SMPS is usually the answer here. Unless you are facing a gazillion units
per year I would look for off-the-shelf wall wart type supplies or small
power bricks that are rated for wide input voltage (90V to 260V or so).

Regards, Joerg

 

[Fred]

Hello Fred,



SMPS is usually the answer here. Unless you are facing a gazillion units
per year I would look for off-the-shelf wall wart type supplies or small
power bricks that are rated for wide input voltage (90V to 260V or so).

Regards, Joerg

Hi Joerg,

Thanks for the reply. There could well be a large quantity of these
supplies needed.

Regards,

Fred

 

[Joerg]

Hello Fred,

Thanks for the reply. There could well be a large quantity of these
supplies needed.

Look at power supplies like these:
http://rocky.digikey.com/WebLib/CUI Inc/Web data/DMS120085-P5-IC.pdf

About $15 if you buy 100 and IIRC they even come with adapters for
several countries.

There are many more companies that make such supplies. Astec etc.

Regards, Joerg

 

[Rich Grise]

I'm looking for a means to inexpensively implement subject PS from a
240/120 mains supply without using a switch. Yep, I know that a SMPS
would do the job but can the job be done at less cost?

What I've looked at so far:

1) Capacitive Transformer. It looks like it might work except that I end
up needing large 22uF high voltage caps on the front end which are
expensive. Needs a switch.
2) Zener supply. Way too much power dissipated in the resistors. Needs a
switch.
3) CT transformer. Looks good but needs a switch.

Any bright ideas or is SMPS the solution??

When you say, "without a switch", do you mean, without having to
manually switch a toggle switch or slide switch?

I knew a guy once who made 120/240 battery chargers, and he used
a 240V relay. At 120V line voltage, it didn't pull in, so the
primaries were in parallel. At 240, the relay pulled in, and put
the primaries in series. A relay _does_ do switching, but I've
never heard a relay called a "switch".

Other than that, probably an SMPS, sorry.

Good Luck!
Rich

 

[martin griffith]

When you say, "without a switch", do you mean, without having to
manually switch a toggle switch or slide switch?

I knew a guy once who made 120/240 battery chargers, and he used
a 240V relay. At 120V line voltage, it didn't pull in, so the
primaries were in parallel. At 240, the relay pulled in, and put
the primaries in series. A relay _does_ do switching, but I've
never heard a relay called a "switch".

Other than that, probably an SMPS, sorry.

Good Luck!
Rich

ISTR that the famous legal firm, Dolby Labs had a product that had a
suitably rated light bulb in series with the transformer primary for
just this function. It helps if you have a constant power requirement



martin

 

[John Woodgate]

I'm looking for a means to inexpensively implement subject PS from a
240/120 mains supply without using a switch. Yep, I know that a SMPS
would do the job but can the job be done at less cost?

Dolby Labs made a laboratory noise-weighting filter, with lower power
consumption certainly, that did 120/240 V by putting a filament lamp in
series with the primary of the mains transformer. The primary voltage
stayed at about 90 V irrespective of the input voltage.

 

[martin griffith]

Dolby Labs made a laboratory noise-weighting filter, with lower power
consumption certainly, that did 120/240 V by putting a filament lamp in
series with the primary of the mains transformer. The primary voltage
stayed at about 90 V irrespective of the input voltage.

Ah, The light bulb, probably the worlds' simplest XOR gate


martin

 

[John Fields]

Hi All,

I'm looking for a means to inexpensively implement subject PS from a
240/120 mains supply without using a switch. Yep, I know that a SMPS
would do the job but can the job be done at less cost?

What I've looked at so far:

1) Capacitive Transformer. It looks like it might work except that I end
up needing large 22uF high voltage caps on the front end which are
expensive. Needs a switch.
2) Zener supply. Way too much power dissipated in the resistors. Needs a
switch.
3) CT transformer. Looks good but needs a switch.

Any bright ideas or is SMPS the solution??

Why can't you just use a wall-wart, and what's this "switch" you
keep referring to?

 

[Joerg]

Hello John,

...

Why can't you just use a wall-wart, and what's this "switch" you
keep referring to?

Guess he means the 120/240 selector. Anyway, wall wart or power brick is
the way to go. Much easier during the agency approval.

Regards, Joerg

 

[Pooh Bear]

Why can't you just use a wall-wart, and what's this "switch" you
keep referring to?

He wants a 'universal' PSU without the need to change voltage taps. See "
240/120 mains supply without using a switch ".

For all practical purposes therefore, an SMPS.

Graham

 

[Pooh Bear]

Hello Fred,


Look at power supplies like these:
http://rocky.digikey.com/WebLib/CUI Inc/Web data/DMS120085-P5-IC.pdf

About $15 if you buy 100 and IIRC they even come with adapters for
several countries.

There are many more companies that make such supplies. Astec etc.

Probably about $6 or less if it comes from China.

Graham

 

[Pooh Bear]

Hi All,

I'm looking for a means to inexpensively implement subject PS from a
240/120 mains supply without using a switch. Yep, I know that a SMPS
would do the job but can the job be done at less cost?

What I've looked at so far:

1) Capacitive Transformer. It looks like it might work except that I end
up needing large 22uF high voltage caps on the front end which are
expensive. Needs a switch.
2) Zener supply. Way too much power dissipated in the resistors. Needs a
switch.
3) CT transformer. Looks good but needs a switch.

Any bright ideas or is SMPS the solution??

3 watts makes a simple switcher just about viable.

I googled "power adaptor china".

One interesting hit was this.

http://www.manufacturers.com.tw/electronics/Power-Adapters.html

There's *tons* of outfits making this stuff out there.

Graham

 

[John Fields]

Hello John,


Guess he means the 120/240 selector.

 

[Fred]

Fred wrote:




3 watts makes a simple switcher just about viable.

I googled "power adaptor china".

One interesting hit was this.

http://www.manufacturers.com.tw/electronics/Power-Adapters.html

There's *tons* of outfits making this stuff out there.

Graham

Hello Again,

Thanks to everyone that has contributed to this thread. I do appreciate
the input. To confirm a question back a post or two, yes, we are looking
for a PS that adapts to 120/240 mains input.

Regards,

Fred