Re: Feedback for low frequency PWM regulator


"Jim Thompson" <To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote in message news:b75774tr39mbc1bc79qdatpneq7oo2hovh@xxxxxxxxxx

On Tue, 08 Jul 2008 15:01:22 GMT, "HarryD" <harryd@xxxxxxxxxxxxx>
wrote:


"JMini" <j.minihane@xxxxxxxxxxxxxxxx> wrote in message
news:X9Hck.662$HY.403@xxxxxxxxxxx
On 7/7/2008 4:35:54 PM, "HarryD" wrote:

"JMini" <j.minihane@xxxxxxxxxxxxxxxx> wrote in message
news:TOuck.637$HY.46@xxxxxxxxxxx
On 7/7/2008 4:08:49 PM, "HarryD" wrote:

"HarryD" <harryd@xxxxxxxxxxxxx> wrote in message
news:E9tck.166176$3p2.98604@xxxxxxxxxxxxxxxxxxxxxxxxx

way. A better way may be controlling current thru the lamp. VFF is a
simple current control. We need a plot of lamp current and power vises
luminous intensity. I'm betting on current being the more linear and
best
to control intensity. Where is Don Klipstein when you need him? Sorry
if
this is a rehash.

Cheers,
Harry
I see a chart on Wikipedia (SP?) of efficacy (Lm/W) for 120W lamps
from
5W to 300W and the efficacy changes from 5 to 20.7. Power dissipated in
the lamp is not good intensity control, maybe current control is just
as
good or better? It sure is simpler!
Cheers,
Harry




After further review, VFF (Voltage Feed Forward) would keep the voltage
across the lamp constant with changes of input voltage. The current would
vary with filament resistance. Now, is controlled voltage adequate for
your application? If yes, a simple VFF, one 8 pin IC, will do the trick.
We still need the curves of lamp Voltage, Current and Power vs. Luminous
intensity output to determine the best variable to control.
Cheers,
Harry



There are at least 20 different bulbs that could be used. That's why I'm
hesitant to try controlling luminous intensity or something other than a
basic electrical property. Voltage or current. But would it be possible to
use VFF in a low frequency design and limit RMS current to the bulb?

VFF will control average voltage across the lamp. Since the waveforms are
almost constant, the RMS voltage across the lamp is just a constant factor.
This is the first circuit you should try and then see what else is needed.
Tell me your requirements, input voltage range, switching frequency,
dimming control voltage, lamp current, lamp control voltage range and any
other info necessary. If you have parts already selected, I will try to use
them. A simple pdf design on "alt.binaries.schematic.electronic" will be
posted for your viewing pleasure.
Cheers,
Harry

Brings to mind, why not just regulate the bulb current?

...Jim Thompson
That was my first thought. Slightly harder than VFF because of current sensing. IMHO the OP has not tried the simple things to determine what is adequate for his application. Sometimes you have to put the pencil down and grab the soldering iron. If the human eye is in the loop, it is very insensitive to light intensity changes and control methods must be tried. So the order of progression from simple to difficult control, voltage, current and then power. In most lighting applications I have seen, current is the best parameter to control.
Cheers,
Harry


.

Relevant Pages

  • Re: Feedback for low frequency PWM regulator
    ... A better way may be controlling current thru the lamp. ... simple current control. ... VFF (Voltage Feed Forward) would keep the voltage ...
    (sci.electronics.design)
  • Re: Feedback for low frequency PWM regulator
    ... A better way may be controlling current thru the lamp. ... simple current control. ... VFF (Voltage Feed Forward) would keep the voltage ...
    (sci.electronics.design)
  • Re: Feedback for low frequency PWM regulator
    ... simple current control. ... We need a plot of lamp current and power vises ... to control intensity. ... VFF (Voltage Feed Forward) would keep the voltage ...
    (sci.electronics.design)
  • Re: Feedback for low frequency PWM regulator
    ... He needs to regulate the power in a resistive load. ... cycle is inversely proportional to the square of the supply voltage. ... A better way may be controlling current thru the lamp. ... simple current control. ...
    (sci.electronics.design)
  • Re: Feedback for low frequency PWM regulator
    ... simple current control. ... We need a plot of lamp current and power vises ... to control intensity. ... across the lamp constant with changes of input voltage. ...
    (sci.electronics.design)
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