• about Test & Measurement
  • Published in issue 5/2012 on page 34
About the article
Lossless Load

Lossless Load

Smart circuit keeps energy waste low

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