Old 09-11-2012, 04:50 PM #1
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Exclamation Dummy load help!!!

Hi LPF, I built a dummy load and done some preliminary tests (don’t have driver yet) with a battery. The battery’s voltage is 7.65 volts and I was doing some test for a 650nm diode (4 diodes in series). When I tested the dummy load and read the voltage in mV on DMM across the 1 ohm resistor it gave me only 700mV??? Is this normal, is it because I used a battery instead of a driver? I got the circuit from bobhaha’s “How to build a selectable dummy load” tutorial and I use 1N4001 diodes and a low tolerance 0.5 watt resistor. Any help would be appreciated!!!!


Circuit (component side):


Solder joints:




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Old 09-12-2012, 03:06 PM #2
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Default Re: Dummy load help!!!

Why don't you do some other voltage measurements around the circuit? Also provide a drawn circuit, as trying to debug some random board with components isn't a walk in the park.
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Old 09-12-2012, 04:21 PM #3
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Default Re: Dummy load help!!!

used this circuit: Got it from bobhaha



Voltage across the 4 diodes is 3.35 volts and the voltage across each diode is 0.83 volts. again the voltage across the resistor stays the same but decreases the longer I keep it running
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Old 09-12-2012, 06:05 PM #4
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Default Re: Dummy load help!!!

Dummy loads are for drivers. If you hook it up to a battery like that, it just acts as a short.

Use a driver.
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Old 09-12-2012, 09:03 PM #5
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Default Re: Dummy load help!!!

^Sorry, just realized that (I feel so stupid!!) Thank you for correcting me!!!
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