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Old 4th February 2013, 09:05 PM   #1
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Default Is this also a type of Switching Power Supply

I came across topologies for power supplies at
SMPS Power Supply Topologies: Comparison and Selection

How I am not sure will my circuit can be called as SMPS ?

[img=http://s4.postimage.org/82s7hyicp/testbucksmps.jpg]
Click the image to open in full size.

In this circuit the transistor starts charging the capacitor as long as OP voltage is less than the input reference V4 Voltage.
I have been able to run it upto 2amps in LT spice

I have also been able to significantly smooth output by lowering the output capacitor and adding an high value inductor.
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Old 4th February 2013, 09:11 PM   #2
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Its not switching it is a linear regulator.
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Old 4th February 2013, 10:46 PM   #3
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Quote:
Originally Posted by nigelwright7557 View Post
Its not switching it is a linear regulator.
Thank you for your reply. If instead of capacitor there was a resistance then I would agree with you and call it linear.

Linear are inefficient. This is more efficient as it does not waste but store voltage in capacitor and release it. Also it has a switching component to it.
The output actually oscillates between in a narrow range but the oscillations were reduced by using a smaller cap.
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Old 5th February 2013, 02:50 AM   #4
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I saw this
File:Low Drop Voltage Regulator.png - Wikipedia, the free encyclopedia
and it looks same as my circuit, so it must be linear regulator too


I am confused as for a 2ms timescale 100uf C1, I see this switching pattern.

Click the image to open in full size.
images
Current going from transistor emitter

and yet for some values i see a constant drain of 2amps, and if its a constant 2 amp then i agree its a loss as voltage drops n heats up the switching transistor.

But looking at the switching pattern, is it STILL not switched power supply
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Old 5th February 2013, 02:55 AM   #5
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Its linear because Q1 works in linear mode.

In a pure switching supply the transistor is fully on or fully off.
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Old 5th February 2013, 03:11 AM   #6
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Thank you for your patience, 1 last question
I agree with you the Q1 is operating in linear mode.you are awesome
the Vb is constant 3.7volts, Ib is also constant 2.2 mA

Still I wonder why this circuit is running at 100% efficiency.
3 ohm load
input 10 volts to 3 volts
Still 1amp flows, that's 100% efficient

This images shows emitter current
Click the image to open in full size.
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Old 5th February 2013, 03:16 AM   #7
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Quote:
Originally Posted by Amit_112dB View Post
Still I wonder why this circuit is running at 100% efficiency.
It cant be 100% efficient, there must be some losses in Q1 when it is conducting.

Even a switching regulator has some losses even though they are small.
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Old 5th February 2013, 03:22 AM   #8
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Quote:
Originally Posted by nigelwright7557 View Post
It cant be 100% efficient, there must be some losses in Q1 when it is conducting.

Even a switching regulator has some losses even though they are small.
I was wrong. Yes there is a terrible loss and its linear.
Thanks you Nigel. now i can sleep without nightmares
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