Quote:
Originally Posted by JimF
I agree that the product design was mostly smoke and mirrors b/c power is power. In a conversation w/ a 'technical' person, I never could get an answer to how it could dissipate less power than a 'standard' regulator.
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I cannot tell you how that particular piece works, but I can tell you how this could be done.
The stock regulator has a power transistor that controls a partial load by imposing a constant restriction to the current. That is, the transistor runs at a partial conductance at all times.
Computer power supplies have a similar circuit to control the voltage to the system, but the industry left partial-saturation devices in the dust bin long ago. Rather, they use what is called a "switching" supply, which runs the transistors with either zero or full conductance. When you quickly switch a MOSFET to control the power (with PWM, for example), the only time the MOSFET actually uses any power is during the switch itself, and that switch is very, very fast.
If you never have partial conductance, you aren't doing any work and you don't have to release heat. Computer power supplies went this way to save power. Of course, since the MOSFETs aren't perfect and do actually have a (small) switching time, there is some heat released. But that heat is minimal compared to a similar circuit using a bipolar transistor in partial-saturation mode.
06-10-2008, 01:56 PM
Hybrid Mode
