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Low drop regulators

Hi,

I'm wondering what are the principles used in low drop regulators.

I 'm trying to make one using standard components, I started by using a zener and a resistance, the closer I could think to a low drop regulator. However there is a constant current draw independant of the load.

I tried then to use a transistor with a fixed voltage at the base (provided by a LED), and then using the fact that VBE is constant =

0.6V. However there is still a voltage drop across the transistor.

So, can one achieve almost 0V drop in some regulators ?

Thanks, vic

Reply to
vic
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Use a PNP for your series pass element (with the emitter going to
your raw +DC and the collector going to your load) and you\'ll be
able to get the voltage drop across the transistor to Vce(sat),
which is a lot better than than you can get with the transistor
wired as an emitter follower.
Reply to
John Fields

The low drop regulators all use a pass element (either bipolar junction transistor or mosfet) operating in inverting mode. For a positive regulator, this implies either a PNP transistor or a P channel mosfet. This also means that the pass element is acting, not as a follower (with its inherent fast negative feedback) but as a voltage amplifier that needs external voltage feedback to control the output voltage. It is also a lot harder to stabilize over a wide range of output current, and in the case of the PNP pass element, adds the base current requirement to the load current requirement to come up with the total input current.

You might look at the equivalent schematics for some of the integrated low drop regulators to see what kind of circuit performs this function.

Reply to
John Popelish

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