Electronics > Beginners
Linear regulator boost with NPN transistor
<< < (5/5)
sureshot:
I think the npn collector should be the regulated input potential, not sure how there's a third terminal. I didn't notice that until you mentioned it. My full rectifier voltage multiplier mock up had the two terminals from the capacitors + - one from each capacitors.
Zero999:

--- Quote from: not1xor1 on July 10, 2018, 03:09:58 pm ---
--- Quote from: Hero999 on July 09, 2018, 10:43:42 am ---Yes, the base emitter voltage increases the drop-out voltage and worsens the regulation.

No base resistor is required, because the base current is self-limiting. When the transistor turns on, the voltage at the emitter rises, reducing the potential difference between the base-emitter junction, therefore the base current, until an equilibrium is reached. This is an example of negative feedback. Look up emitter follower.

An NPN transistor can be  used, with a PNP transistor, as per the schematic I posted in the other thread.
https://www.eevblog.com/forum/beginners/voltage-multiplier-120443/msg1648847/#msg1648847

--- End quote ---

Hi Hero999
I do not understand how that circuit is supposed to work.
If the purpose is to get a low dropout (through an higher voltage to the NPN base) then the input Voltage labels have been exchanged.

The PNP + the IC should be supplied by the voltage doubler solving the problem of the higher dropout, while the NPN collector (or that of an array of power NPN transistors + ballast resistors) should be connected to the rectified voltage. Then the minimum dropout would be the saturation voltage of the NPN transistor(s + ballast resistors drop).

--- End quote ---
You're right. I got them the wrong way round. Here's the correct schematic.



--- Quote from: sureshot on July 10, 2018, 06:18:08 pm ---I think the npn collector should be the regulated input potential, not sure how there's a third terminal. I didn't notice that until you mentioned it. My full rectifier voltage multiplier mock up had the two terminals from the capacitors + - one from each capacitors.

--- End quote ---
The VDoubler terminal is for the voltage doubler, which can be used to reduce the drop-out voltage to just the tranistor's saturation voltage. If you don't have a voltage doubler, just connect it to the VRectifier and it will work, but with a higher drop-out voltage of about 3V, at full load.
sureshot:
Yes ok I get it, thanks for putting me straight on that, I might, only might, lol have been doing some head scratching somewhere down the the line.
Navigation
Message Index
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod