[sdiy] When to use voltage regulators and when to use resistors?

[Philippe Derenne]

Hi James,

Depending on the current drawn by the 15 V modules, the resistor will need 
to dissipate more or less power.
For 100 mA, R will be 35 ohms, let's say 33, and will handle 0.33 W.
For 500 mA, R will be 7 ohms, let's say 6.8, and will handle  1.7 W.
For 1 A,  R will be 3.5 ohms, let's say 3.3, and will handle  3.3 W.

Another point : when you'll add more modules, you'll need to adjust the 
resistor to keep the right voltage

I would use a resistor (and a zener) for a few mA, but for 50 mA and up, I'd 
go for the 7815, or another discrete components (zener and transistor) 
regulator.

Phil.

----- Original Message ----- 
From: "James R. Coplin" <james at ticalun.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, May 25, 2008 2:09 AM
Subject: [sdiy] When to use voltage regulators and when to use resistors?


> Probably a pretty silly question but I'm wondering when to consider 
> voltage
> regulators versus knocking down voltage with resistors.  In my particular
> case, I'm adding some modules to my rack mounted SEMs.  The SEMs run off 
> of
> 18.5v but the additional circuitry I want to add expects 15v.  Should I 
> put
> a 15v regulator on or can I just pad down the 18.5 volts coming from the
> power supply with appropriate resistor values?  I have plenty of spare
> amperage in the supply to handle the additional modules, I'm just not so
> sure about getting the voltage down to the 15v. Thanks!
>
> James R. Coplin
> (郭杰明)
>
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