Macwarrior
New Member
Hey --
I'm trying to make a small LED lamp that runs on a 9-volt battery. It would use 4 white LEDs, 3.5v each. I can't run them in series (3.5 * 4 = 14), but if I try to run them in parallel (at 20mA nominal current), my calculations tell me that I'll need at least a 1W resistor to dissipate all that extra power. I don't really want a giant hot resistor eating up my battery, so here's my question:
Can I hook the LEDs up in a parallel-series circuit, with 2 sets of LEDs in series, connected in parallel? It simplifies to a pair of (7-volts-drop at 20mA) circuits in parallel, which manages to decrease the resistor requirement to something like 0.08W/56ohm. In addition to less heat and wasted power, it's nice that I can use cheap 1/4Ws.
This seems okay, but seeing as I have very little experience with electronics, I thought I'd check it out here - am I defying any laws of physics or electronics by doing this?
Thanks very much
Macwarrior
(oh, and if the power is backwards in the diagram, ignore it - I always forget which way a diode diagram is polarized)
I'm trying to make a small LED lamp that runs on a 9-volt battery. It would use 4 white LEDs, 3.5v each. I can't run them in series (3.5 * 4 = 14), but if I try to run them in parallel (at 20mA nominal current), my calculations tell me that I'll need at least a 1W resistor to dissipate all that extra power. I don't really want a giant hot resistor eating up my battery, so here's my question:
Can I hook the LEDs up in a parallel-series circuit, with 2 sets of LEDs in series, connected in parallel? It simplifies to a pair of (7-volts-drop at 20mA) circuits in parallel, which manages to decrease the resistor requirement to something like 0.08W/56ohm. In addition to less heat and wasted power, it's nice that I can use cheap 1/4Ws.
This seems okay, but seeing as I have very little experience with electronics, I thought I'd check it out here - am I defying any laws of physics or electronics by doing this?
Thanks very much
Macwarrior
(oh, and if the power is backwards in the diagram, ignore it - I always forget which way a diode diagram is polarized)