Zero Feedback Regulator
- Thread starter poynton
- Start date
Andy,
If you really mean "zero feedback", then it is not a regulator.
Even the most basic shunt regulator with only a resistor and zener diode uses negative feedback. If the load current changes, the zener voltage tends to change. This is detected by the zener and, as a result, the zener changes it's current in order to keep the voltage change small. This is negative feedback. Another way to think about this is that the zener has a transfer function between it's voltage (input) and it's current (output), even thought it is non-linear.
Rick
If you really mean "zero feedback", then it is not a regulator.
Even the most basic shunt regulator with only a resistor and zener diode uses negative feedback. If the load current changes, the zener voltage tends to change. This is detected by the zener and, as a result, the zener changes it's current in order to keep the voltage change small. This is negative feedback. Another way to think about this is that the zener has a transfer function between it's voltage (input) and it's current (output), even thought it is non-linear.
Rick
The quote, in post 1, is from an Ebay listing for a "high-end" nos DAC.
http://cgi.ebay.co.uk/ws/eBayISAPI....m=270202929616&ssPageName=STRK:MEWA:IT&ih=017
I asked the question as I could not work out how a regulator could regulate without feedback of some sort.
As you say, even a basic zener / transistor stabiliser could be said to have a degree of feedback.
It's probably BS !
Andy
http://cgi.ebay.co.uk/ws/eBayISAPI....m=270202929616&ssPageName=STRK:MEWA:IT&ih=017
I asked the question as I could not work out how a regulator could regulate without feedback of some sort.
As you say, even a basic zener / transistor stabiliser could be said to have a degree of feedback.
It's probably BS !
Andy
sawreyrw said:
Rick, the zener voltage doesn't change. It works even better if the zener is an ideal voltage source. What is changed is the sample of Vout that goes back to the shunt reg (the base or emitter of a transistor mostly) which increases the difference between that sample and the constant zener voltage. That increase in difference increases (or decreases depending on topology) the 'regulator' output to make Vout again what it was supposed to be.
Jan Didden
caling Charles Hansen
The only other references I have found are on pedja's pages :-
http://www.pedjarogic.com/gc/supplies.htm
( which is a zener stabilised supply )
and a reference by Charles Hansen :-
http://www.diyaudio.com/forums/showthread.php?threadid=115513&perpage=25&pagenumber=5 post 116
( Unspecified )
Andy
The only other references I have found are on pedja's pages :-
http://www.pedjarogic.com/gc/supplies.htm
( which is a zener stabilised supply )
and a reference by Charles Hansen :-
http://www.diyaudio.com/forums/showthread.php?threadid=115513&perpage=25&pagenumber=5 post 116
( Unspecified )
Andy
Jan,
My post regarding the simple shunt regulator is correct. Note that the circuit consists of only a resistor and a zener diode. Yes, the zener voltage does change.
Even if the zener was idea, like a perfect voltage source once it begins to conduct, the decsription would still be correct. The volt change would then be zero because the incremental transconductance (delta I / delta V) would be infinite.
Rick
My post regarding the simple shunt regulator is correct. Note that the circuit consists of only a resistor and a zener diode. Yes, the zener voltage does change.
Even if the zener was idea, like a perfect voltage source once it begins to conduct, the decsription would still be correct. The volt change would then be zero because the incremental transconductance (delta I / delta V) would be infinite.
Rick