REGISTER | LOGIN
Home    Bloggers    Blogs    Article Archives    Messages    About Us   
Tw  |  Fb  |  In  |  Rss
Dennis Feucht

High-Efficiency Analog Amplifiers, Part 2: Series and Parallel Segmented Amplifiers

Dennis Feucht
steve.taranovich
steve.taranovich
1/8/2018 4:37:57 PM
User Rank
Blogger
Re: Reverse Vbe problem
I have fixed the error under the text---thanks Dennis

50%
50%
D Feucht
D Feucht
1/8/2018 3:39:43 PM
User Rank
Blogger
Re: Reverse Vbe problem
Brad,
First, there is an error in the text. The line under the first circuit diagram,

"...the diode conducts and QL+ is cut off." should read QU+ instead of QL+.

Second, as to your point, yes, a series base or emitter diode would be required (or some similar fix) to keep from breaking down the b-e junctions.


Actually, I prefer the parallel-segmented scheme, perhaps because I've used it, even though it requires a few more parts. For it, only one BJT conducts per segment and it is thus somewhat more efficient. For an IC implementation, the  extra parts are trivial. The comparator input characteristics can be sloppy; a commodity-grade LM339 would be quite adequate.

50%
50%
bpeeters
bpeeters
1/8/2018 2:49:07 PM
User Rank
Newbie
Reverse Vbe problem
Doesn't look like there are enough diodes in the Series Segmented Amplifier circuit.  With zero signal, for example, QU+ is going to experience most of +Vg1 across its base-emitter junction reverse biased.  Unless +Vg1 is very low voltage, e.g., less than 8 volts or so, this is likely to exceed the reverse-breakdown spec of the NPN QU+ transistor.  This could probably be fixed with another diode in series with the QU+ emitter and some careful biasing resistors to ensure the emitter can follow the base down below the Vg1+ supply voltage.  Alternatively, might be able to protect the base-emitter junction with a diode in series with the base.

It's a neat concept to reduce wasted power in an analog amplifier, but I suspect the schematic shown is "simplified" for illustrative purposes.  A real-world implementation would have a lot of additional details needed to make it actually work and not blow out the transistors, right?

Best, Brad

 

50%
50%
More Blogs from Dennis Feucht
One of the seemingly most difficult aspects of power electronics is how to design power inductors and transformers.
In Part 1, the op-amp was approximated from a single-pole, finite gain amplifier to an infinite-gain, single-pole op-amp, and the gain of the transresistance amplifier circuit, shown repeated below, was derived. In this Part 2 we look at the consequences.
This is a throw-together project using junk box parts that can be useful whenever an interesting-looking waveform is needed for a demonstration or for the beginnings of a video test generator or curve tracer.
A seemingly simple circuit with only two components, an op-amp and a feedback resistor, is commonly used to convert a current to a voltage. This circuit is familiar as a photodetector or impedance-meter current-sense amplifier.
Oscilloscope triggering circuits can be adapted to other applications, as precision synchronizers. Both analog and digital ‘scope triggering has been enhanced by various auto-trigger schemes. This tutorial overview of ‘scope triggering circuits and schemes presents the basics of trigger generators and also some enhancements
flash poll
educational resources
 
follow Planet Analog on Twitter
Planet Analog Twitter Feed
like us on facebook
our partners
Planet Analog
About Us     Contact Us     Help     Register     Twitter     Facebook     RSS