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Hi everyone,

I’ve been trying to build a multiple-load voltage divider that applies a negative voltage to one of the loads. I’ve followed the steps and example given in "Practical Electronics for Inventors" by Paul Scherz.

Using the circuit from the book and the specified load requirements, everything works perfectly. However, when I define my own loads and change the voltages, I can never seem to achieve the desired result using exactly the same technique described in the book.

I’m wondering if I’m missing something fundamental in the way I’m setting up or calculating the circuit.

Has anyone come across this before, or could point me in the right direction?

This is the example from the book:

This is the version I built:

The resistor making the divider should be at least 10 times smaller than the resistance of the "loads". (100 and 1000 times is even better)

As example, if you divide 170V with two one ohm resistors in series, add a load of 1 kilo-ohm in parallel to one of the two initial resistors and the voltage is still close to 170 V/ 2.

But it is definitively a WASTE of energy since a relatively large current will go through the small resistor and the resistor must be small (in comparison to the load) to be an effective voltage divider. Other alternatives are often considered because of that "energy weakness" of resistors to divide voltages (efficiently independantly of the loads), unless the to be applied loads are already large. (But large resistors are known to be "noisy"). Also consider the size of a one ohm resistor if subjected to 170V, ... that makes close to ... 29 kiloWatt !!! You could melt steel with that in less time than to say "rabbit" (or hopefully the in-house breaker will pop-out before without becoming a fire hazard).