Controlling 220V ac using 5V analog signal

[shehry]

Hi,

I am looking for a FET which would help me in controlling a 220V ac
signal using a 0-5 V analog signal. i dont know of any transistors with
such characteristics.

i thought of doing this by first using a transformer to bring the 220
down to some reasonable value, then pass it through the FET and then
pass the signal again through a similar transformer. But all this seems
a bit too redundant. there has to be a simpler way to it, i am sure.

i also thought of using a relay but that wouldnt do at all because i
need the output as a function of my input.

i guess all i need is a voltage controlled potentiometre but that 220V
ac is confusing me.

Could anyone help.

 

[Wolfgang Mahringer]

Hi shehry,

I am looking for a FET which would help me in controlling a 220V ac
signal using a 0-5 V analog signal. i dont know of any transistors with
such characteristics.

i guess all i need is a voltage controlled potentiometre but that 220V
ac is confusing me.

May be you should tell us what you are trying to build.
It sounds all too weird....

regards,
Wolfgang

 

[shehry]

sorry if i couldnt explain it correctly.

actually we were trying to make a motor speed controller. i was trying
to use a sewing machine motor.

i thought of generating an analog signal using a microcontroller and
using that signal i wanted to control the amount of voltage that would
go to the motor at the end of the day.

in other words i was trying to replace the pedal of the sewing machine
by an electric signal.

hopefully it clears up the mess i created above

 

[Phil Allison]

"shehry"

sorry if i couldnt explain it correctly.

actually we were trying to make a motor speed controller. i was trying
to use a sewing machine motor.

i thought of generating an analog signal using a microcontroller and
using that signal i wanted to control the amount of voltage that would
go to the motor at the end of the day.

in other words i was trying to replace the pedal of the sewing machine
by an electric signal.

** The usual and most efficient method to control a "universal motor " is
to use a triac.

Try searching Google with "triac" and "phase control".

Also see "opto isolator" & "triac driver ".



.......... Phil

 

[shehry]

Thanks for your help Phil.

i made a search on the keywords that you recommended and i tried to
study the working of the triac in one or two books. But i am getting
confused on one point. Can i make a variable speed controller using
triacs?

The way i see it, a triac will help me in triggering the motor on but
it wont help me in controlling the speed as a "function" of the gate
voltage.

 

[shehry]

sorry...i got the idea.

it has to be dependent upon the width of the gate voltage.

thanks for your help

 

[DaveM]

sorry...i got the idea.

it has to be dependent upon the width of the gate voltage.

thanks for your help

I don't think you have the right idea... yet. The timing of the trigger
pulse in relation to the AC wave is what will control the output.
Think about the plain old light dimmer. It controls a light bulb brightness
by varying the timing of the triac trigger pulse. The closer the trigger to
the start of the AC waveform, the higher the output voltage, thus, the
brighter the light.
Matter of fact, if a sewing machine motor is what you want to control, a
dimmer will probably work just fine. You might want to put a snubber
(series resistor/capacitor) across the triac, but I think it would be your
simplest solution. I've been using light dimmers to control the speed of
ceiling fans for many years.. . never had a failure.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

[Ignoramus9142]

Hi,

I am looking for a FET which would help me in controlling a 220V ac
signal using a 0-5 V analog signal. i dont know of any transistors with
such characteristics.

i thought of doing this by first using a transformer to bring the 220
down to some reasonable value, then pass it through the FET and then
pass the signal again through a similar transformer. But all this seems
a bit too redundant. there has to be a simpler way to it, i am sure.

i also thought of using a relay but that wouldnt do at all because i
need the output as a function of my input.

i guess all i need is a voltage controlled potentiometre but that 220V
ac is confusing me.

What do you mean by controlling? You can turn 220V on and off using a
"solid state relay".

Try searching ebay for "crydom solid state relay".

They are very easy to use.

If you want some other kind of control, then it would be interesting
to see what.

i

 

[Jasen Betts]

Hi,

I am looking for a FET which would help me in controlling a 220V ac
signal using a 0-5 V analog signal. i dont know of any transistors with
such characteristics.

a servo-driven Variac would be one way....

smething involving a triac and an optocupler or two might be cheaper.
ISTR in the depths of time a colour organ (basically 4 low voltage
controlled mains light dimmers) in a Brittish electonics mag,
(so 230V but that should be close enough to 220 for practical purp0oses

I guess all i need is a voltage controlled potentiometre but that 220V
ac is confusing me.

voltage controlled potentiometers that can withstand 220V AV are pretty rare.
most are made for around 1V

Could anyone help.

Bye.
Jasen

 

[Jasen Betts]

Thanks for your help Phil.

i made a search on the keywords that you recommended and i tried to
study the working of the triac in one or two books. But i am getting
confused on one point. Can i make a variable speed controller using
triacs?

The way i see it, a triac will help me in triggering the motor on but
it wont help me in controlling the speed as a "function" of the gate
voltage.

phase control.... if you trigger the triac late then the motor missess out
on some of each half cycle.

what you do is arrange for your microcontroller to get a signal every time
the mains changes polarity (aka zero crossing) and then use one of its
internal timers to delay some amount of time from getting that signal
before triggering the triac.

The longer the delay the slower the motor runs.

 

[scada]

sorry if i couldnt explain it correctly.

actually we were trying to make a motor speed controller. i was trying
to use a sewing machine motor.

i thought of generating an analog signal using a microcontroller and
using that signal i wanted to control the amount of voltage that would
go to the motor at the end of the day.

in other words i was trying to replace the pedal of the sewing machine
by an electric signal.

hopefully it clears up the mess i created above

I have actually made this very thing! I restored a 1922 Singer machine and
cabinet. I used an SCR triggered off the positive peak through a diode and a
pot across an RC circuit to trigger the gate (that's the basic of it, I can
post the schematic if you need it). This is your basic light dimmer circuit,
only they use a triac. I was not interested in speed, or torque at the time
the unit was strictly for show. An off the shelf light dimmer should work
for you, just make sure the motor is the "Universal" type (has brushes - AC
& DC).

 

[Spehro Pefhany]

Hi,

I am looking for a FET which would help me in controlling a 220V ac
signal using a 0-5 V analog signal. i dont know of any transistors with
such characteristics.

i thought of doing this by first using a transformer to bring the 220
down to some reasonable value, then pass it through the FET and then
pass the signal again through a similar transformer. But all this seems
a bit too redundant. there has to be a simpler way to it, i am sure.

i also thought of using a relay but that wouldnt do at all because i
need the output as a function of my input.

i guess all i need is a voltage controlled potentiometre but that 220V
ac is confusing me.

Could anyone help.

Get yourself a module designed to do this. Many will take a 0-10V
signal or a pot to control the speed. Make SURE THAT THE INPUT IS
GALVANICALLY ISOLATED FROM LINE VOLTAGE.

It takes maybe 50-100 components to do a good job of this-- the
modules are relatively cheap, safety-agency approved and work well.

 

[Wiwied]

Hi Shehry...

I'm Dwi, a student of Brawijaya University Malang Indonesia.Now I'm
trying to build a dimmer which use MOSFET to control the 220 Vac.Have
you found the complete circuit?If you have,please help me by sending
the circuit to my email account : [email protected]
For your concern, Thank you very much.