PWM Control of a 24Volt (20W) Light Bulb
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Posts: 46,084
I would like to control the brightness of a 24 volt (0.8amp, 20Watt)
halogen light bulb using a BS2P and the PULSOUT command. Looking on page
128 of the Earth Measurements V1.2 shows how to control a low current
5vdc pump using a transistor. Will this approach work using the
appropriately sized transistor (FET, SCR, etc.)? If anyone can point me
towards example circuits I'd appreciate it. I have a solid 5VDC supply
and between 22 and 28VDC for the lamp depending on battery levels
available.
Thanks
Chris
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halogen light bulb using a BS2P and the PULSOUT command. Looking on page
128 of the Earth Measurements V1.2 shows how to control a low current
5vdc pump using a transistor. Will this approach work using the
appropriately sized transistor (FET, SCR, etc.)? If anyone can point me
towards example circuits I'd appreciate it. I have a solid 5VDC supply
and between 22 and 28VDC for the lamp depending on battery levels
available.
Thanks
Chris
________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!
Comments
Yup, it will work the same, and the circuit is the same. The only
diffenrence will be the transistor and the resistor
values. You could use a 2N3055, easily found at Radio Crack. It's a little
over kill, but will last forever.
Jonathan
www.madlabs.info
Original Message
From: "Christopher Dundorf" <cdundorf@j...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, February 14, 2004 11:31 AM
Subject: [noparse][[/noparse]basicstamps] PWM Control of a 24Volt (20W) Light Bulb
> I would like to control the brightness of a 24 volt (0.8amp, 20Watt)
> halogen light bulb using a BS2P and the PULSOUT command. Looking on page
> 128 of the Earth Measurements V1.2 shows how to control a low current
> 5vdc pump using a transistor. Will this approach work using the
> appropriately sized transistor (FET, SCR, etc.)? If anyone can point me
> towards example circuits I'd appreciate it. I have a solid 5VDC supply
> and between 22 and 28VDC for the lamp depending on battery levels
> available.
>
> Thanks
> Chris
>
> ________________________________________________________________
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>
>
>
>
>
>halogen light bulb using a BS2P and the PULSOUT command. Looking on page
>128 of the Earth Measurements V1.2 shows how to control a low current
>5vdc pump using a transistor. Will this approach work using the
>appropriately sized transistor (FET, SCR, etc.)? If anyone can point me
>towards example circuits I'd appreciate it. I have a solid 5VDC supply
>and between 22 and 28VDC for the lamp depending on battery levels
>available.
>
>Thanks
>Chris
No, that circuit is designed to control a 3 volt pump, and you will
need a different circuit to control your 24 volt lamp.
The circuit you referred to uses the transistor in a "common emitter"
configuration to turn the pump ON and OFF. It would also work with
the PWM command to control the speed or power of the pump.
,
Vdd
| /
|'
P3 --/\/\---| ZTX1049 (superbeta e-line)
100 |>
| \ 10ohm
`--/\/\--3vPUMP---Vss
There are a number of circuits you could use to control the 24 volt
lamp. One is a power n-channel mosfet with the lamp in the drain
circuit to 24 volts:
d
||
LAMP
24V
100 g|
P3 --/\/\--o--||--; IRL520
PWM | ||--|
| |s
| 22k |
`-/\/\-|
|
Vss
The 22k resistor pulls the gate of the transistor to ground when P3
happens to be an input. That turns the lamp off. The maximum power
dissipation in the IRL520 would be 12 watts if by some chance the
gate floats, and that would be HOT! With PWM control, the transistor
should not get too hot, because in simple terms it is switching in
PWM between full ON and full OFF, both of which are zero power
dissipation in the mosfet. I reality, the switching takes time and
the transistor warms up.
The Stamp can only do one thing at a time. It can vary the brightness
with a PWM command, but it has to leave the lamp either full on or
full off while it executes other pbasic commands. If you want to set
a medium brightness and then have the Stamp go off and do other
stuff, you will have to look into an external PWM generator.
-- regards,
Tracy
service life. You might look into how they work - Quite
different from incandescents.
regards, Jack
http://www.geocities.com/jimforkin2003/
jim
Original Message
From: Christopher Dundorf [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=YTjoSMBtIJ1bAaGbMpZIG3NWntJOUWtC_gi83l5ZSxBYH6Opb4kKeXw1RLo2VztvaUnAW7-eUs43NA]cdundorf@j...[/url
Sent: Saturday, February 14, 2004 2:31 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] PWM Control of a 24Volt (20W) Light Bulb
I would like to control the brightness of a 24 volt (0.8amp, 20Watt)
halogen light bulb using a BS2P and the PULSOUT command. Looking on page
128 of the Earth Measurements V1.2 shows how to control a low current
5vdc pump using a transistor. Will this approach work using the
appropriately sized transistor (FET, SCR, etc.)? If anyone can point me
towards example circuits I'd appreciate it. I have a solid 5VDC supply
and between 22 and 28VDC for the lamp depending on battery levels
available.
Thanks
Chris
________________________________________________________________
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Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!
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Yahoo! Groups Links
Do you have any PWM Duty Cycle vs Hours of Life curves or know where I
could find them. Depending on the the degree of reduction it might not
be an insurmountable problem.
Thanks for the thought, I never considered this until now.
Chris
<<<>>>
Date: Sun, 15 Feb 2004 07:39:00 -0800
From: goflo@p...
Subject: Re: PWM Control of a 24Volt (20W) Light Bulb
Less than 100% duty cycle significantly reduces Halogen
service life. You might look into how they work - Quite
different from incandescents.
regards, Jack
________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!
I had a little trouble visualizing the character based diagram likely due
to my email shifting spacing around but I think I follow your approach.
Is your design the same as what is shown on Al Williams web link with the
exception of a 100 ohm resistor directly coming off of P3 and before the
junction with the 22K resistor? Is the 100 Ohm for overcurrent
protection to the Stamp in the event that the FET failed?
http://www.al-williams.com/fetrly.htm
As for the "cycle time" of the Stamp I was unaware it worked that way.
What you're saying though makes total sense. On this particular project
I have a single Stamp performing many tasks with about 24+ I/Os in use.
Yikes! Therefor I'm going to take your advice on the external PWM
generator. I've seen several of these units described in N&V magazine.
Thanks for your help,
Chris
<<<>>>
Message: 9
Date: Sat, 14 Feb 2004 15:58:45 -0800
From: Tracy Allen <tracy@e...>
Subject: Re: PWM Control of a 24Volt (20W) Light Bulb
>I would like to control the brightness of a 24 volt (0.8amp, 20Watt)
>halogen light bulb using a BS2P and the PULSOUT command. Looking on
page
>128 of the Earth Measurements V1.2 shows how to control a low current
>5vdc pump using a transistor. Will this approach work using the
>appropriately sized transistor (FET, SCR, etc.)? If anyone can point me
>towards example circuits I'd appreciate it. I have a solid 5VDC supply
>and between 22 and 28VDC for the lamp depending on battery levels
>available.
>
>Thanks
>Chris
No, that circuit is designed to control a 3 volt pump, and you will
need a different circuit to control your 24 volt lamp.
The circuit you referred to uses the transistor in a "common emitter"
configuration to turn the pump ON and OFF. It would also work with
the PWM command to control the speed or power of the pump.
,
Vdd
| /
|'
P3 --/\/\---| ZTX1049 (superbeta e-line)
100 |>
| \ 10ohm
`--/\/\--3vPUMP---Vss
There are a number of circuits you could use to control the 24 volt
lamp. One is a power n-channel mosfet with the lamp in the drain
circuit to 24 volts:
d
||
LAMP
24V
100 g|
P3 --/\/\--o--||--; IRL520
PWM | ||--|
| |s
| 22k |
`-/\/\-|
|
Vss
The 22k resistor pulls the gate of the transistor to ground when P3
happens to be an input. That turns the lamp off. The maximum power
dissipation in the IRL520 would be 12 watts if by some chance the
gate floats, and that would be HOT! With PWM control, the transistor
should not get too hot, because in simple terms it is switching in
PWM between full ON and full OFF, both of which are zero power
dissipation in the mosfet. I reality, the switching takes time and
the transistor warms up.
The Stamp can only do one thing at a time. It can vary the brightness
with a PWM command, but it has to leave the lamp either full on or
full off while it executes other pbasic commands. If you want to set
a medium brightness and then have the Stamp go off and do other
stuff, you will have to look into an external PWM generator.
-- regards,
Tracy
________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!
>Jack,
>
>Do you have any PWM Duty Cycle vs Hours of Life curves or know where I
>could find them. Depending on the the degree of reduction it might not
>be an insurmountable problem.
>
>Thanks for the thought, I never considered this until now.
Don Klipstein' lighting page is a *great* resource for lighting info!
Here's a page that talks about (among other things) failure modes of
incandescent and halogen bulbs (and why halogens don't like to
be dimmed)
http://members.misty.com/don/bulb1.html
Steve
[noparse][[/noparse]Non-text portions of this message have been removed]
> could find them.
No, sorry.
I've seen OEM minimum on-time recommendations for rated life
expectancy - IOW, how long the lamp should stay on once turned
on. Don't remember the numbers, but it was minutes, not milli-
seconds.
regards, Jack