I'm trying to connect 30x small incandescent light bulb in parallel (1.5v / 300mA). But I'm having some issue designing the supply and dimming circuit. Does it just work like LED's for the calculations or shall I take other things in consideration ?

So far my plan is to wire everything in parallel, get my lab supply to throw 1.5v and draw 9A (300mA * 30) and use a MOSFET with a pwm signal from a MUC in order to dim the whole thing.

Does that sound like a good route or am I totally wrong ?

Thank you !

  • \$\begingroup\$ Since they are a (mostly) resistive load, you need no way to control the current like you do with leds \$\endgroup\$
    – PlasmaHH
    Apr 21, 2015 at 9:48
  • \$\begingroup\$ Sounds OK but remember the cold resistance of the bulb is smaller than the hot. Is there any reason why they can't be connected in series/parallel, say 6 groups of 5. (7.5V, 1.8A) ? \$\endgroup\$ Apr 21, 2015 at 9:51
  • \$\begingroup\$ I would like to dim the whole circuit at same brightness. How can I do that if I split the groups ? \$\endgroup\$
    – Waz
    Apr 21, 2015 at 10:33
  • \$\begingroup\$ Series is much more sensible, in the style of Christmas tree lights. You can dim the whole lot in just the same way if they're in series. \$\endgroup\$
    – pjc50
    Apr 21, 2015 at 10:42
  • \$\begingroup\$ And they don't work like LEDs - they don't have a defined forward voltage, they look more like resistors. \$\endgroup\$
    – pjc50
    Apr 21, 2015 at 10:43

1 Answer 1


You could easily connect them all in parallel. or in any grid ie (3*10 or 6*5) and just control the input to the grid independently. As others have said incandescent bulbs is mostly a resistive load. If you go with ,say 5 in series and each of those 5 is in parallel then you would require 7.5V @ 1.8A. Choosing a configuration is simply a matter of what you have available.

Except for requiring more power than LEDs the incandescent bulbs can be pwm much easier. You might even be able to get away with a much lower switching frequency because the bulbs will tend to filter higher frequencies.

Series is easier to switch m but if one bulb do fails , the whole light fails. Going parallel you need to switch a higher current but its trivial to find a blown bulb. Using a grid like arrangement mixes these two features partially so you get lower switching current than when all is in parallel and its easier to find faults than when everything is in series.


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