Re: Newly Designed DX Buck Driver (Kennan Like) 90% Efficiency
Built an LED Turbo Tower for use in SureFire TurboHeads.
I'm a little disappointed with the KD1640 driver that I used. Ordered six of them and this is the only one I've used so far. Driving an XP-G R4, which also underperforms compared to some other XP-G R4s I've gotten.
The KD1640 delivers about 1.05A, so that's good. Right in line with what you'd expect based on the sense resistors.
The first disappointment is that the XP-G R4 Vf ~
[email protected]. True that this is basically in agreement with what is in the datasheet. But I had previously measured about 3.1V for another XP-G at essentially the same drive current. Hot spot lux at 1 meter is also about 10% lower vs the same XP-G with Vf~3.1V. Measuring the XP-G die height is difficult, but the two towers look to be the same within 0.003", so I don't think LED focus is the issue. The reason might be due to LED lumens variation in the R4 bin.
The second disappointment is that the KD1640 seems to have lower efficiency than expected -- about 80%-83% vs the expected ~90%.
The third disappointment is that the KD1640 seems a little unstable for Vin of about 5.0V +0.3V/-0.2V. Power-in takes a repeatable dip starting at about 4.8V, hits the bottom of the dip at 5.0V (~15% drop in power-in), and finally returns to the steady state value at about 5.3V. At least for this specific driver board, using 2x123A might be less desirable than 2x16340 Li-ion. The Power-in vs Voltage-in curve is otherwise reasonably flat when running in regulation (I measured out to 12V).
The last disappointment is that the KD1640 voltage overhead is slightly higher than expected at about 0.7V. Still reasonably good.