Lossless Load

Smart circuit keeps energy waste low

Published in issue 5/2012 on page 34

While the title might sound controversial (a load always dissipates some power), the concept presented in this article is spot on: it mimics a load to in-vehicle circuitry that checks for lamp faults. The circuit is great whenever a glass lamp gets replaced by an energy-saving LED substitute. Remarkably, it does not torch extra energy like a shunt would do. Instead, the Lossless Load briefly stores the energy needed to trick the fault circuitry and feeds it back into the car’s electrical system when appropriate.

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R1,R4 = 6.8kOhm
R2,R3,R7 = 1kOhm
R5,R12 = 10Ohm
R6 = 22kOhm
R8–R11 = 0.47Ohm 0.5W*
R13 = 0.1Ohm 2W *
* see text
C1,C2 = 100µF 35V, low ESR
C3,C4 = 100nF
C5 = 10nF
C6 = 1nF
C7 = 470pF
C8 = 2.2nF
L1,L2 = 10µH, 5A, Würth type 744711005 or Conrad Electronics # 420284
L3 = 100µH, 5A, Würth type7447070 or Conrad Electronics # 438020
D1,D2 = 1N4148
D3 = MBR1045
D4 = P6KE15A, TVS diode 15V 600W
IC1 = UC3845N
T1 = IRFZ48N
P1 = 470 Ohm trimpot
6.35 mm (0.25 in.) spade terminals for PCB mounting
TO220 thermal insulator kit for D43 and T1
Heatsink, 10K/W *
PCB # 110755