Zv6-t?

[Cloth Ears]

Parts and eagerness abound,
But knowledge is lacking.
Sadly, I wait.

Gents,

I'm trying to teach an old dog (me) new tricks. But I'm trying to learn a bit of knowledge first before I embark on a path than may lead to danger.

To this end, I've been trying to grasp some of the Zen variations by reading various tutorials available on the net, and I thinks I've got a bit of a handle on Son of Zen (SOZ) and the variation 6 (ZV6).

But I've been looking at variation 7 (ZV7-R), where an active current source is used and I'm back in the dark ages again.

So, is there a good place to read about active current sources and why they work? I've looked for this on the site, and it generally assumes knowledge and is asking for improvements (or showing them).

Also, is it possible to inductively load ZV6 without resorting to an active current source? Would this also provide efficiency benefits along the lines of variation 7 (ZV7-T), without the added complications (for me)?

[Zen Mod]

Originally posted by Cloth Ears
Parts and eagerness abound,
But knowledge is lacking.
Sadly, I wait.

Gents,

I'm trying to teach an old dog (me) new tricks. But I'm trying to learn a bit of knowledge first before I embark on a path than may lead to danger.

To this end, I've been trying to grasp some of the Zen variations by reading various tutorials available on the net, and I thinks I've got a bit of a handle on Son of Zen (SOZ) and the variation 6 (ZV6).

But I've been looking at variation 7 (ZV7-R), where an active current source is used and I'm back in the dark ages again.

So, is there a good place to read about active current sources and why they work? I've looked for this on the site, and it generally assumes knowledge and is asking for improvements (or showing them).

Also, is it possible to inductively load ZV6 without resorting to an active current source? Would this also provide efficiency benefits along the lines of variation 7 (ZV7-T), without the added complications (for me)?

just download ( if you aren't already ) all zen articles and read them.
after that ,shoot with questions

[Nelson Pass]

Originally posted by Cloth Ears
[i]So, is there a good place to read about active current sources and why they work?

The latest copy of AudioXpress has a great article on current
sources written by Walt Jung. Lesser examples can be found
in pieces at www.passdiy.com

[GRollins]

You're familiar with the idea of a voltage regulator, right? An ideal voltage regulator would deliver any arbitrary amount of current from 0 amps to infinite amps while maintaining an absolutely steady voltage. That's why it's a voltage regulator--the voltage remains constant, no matter what, but the current varies.
Now...call the current source by its alias: current regulator. What's a current regulator do? It locks the current and lets the voltage vary. Suppose you want a steady 1 amp. If you give a 1A current source a 1 ohm load, it will develop exactly 1V across the load. Simple application of Ohm's Law: I*R=E...1A*1 Ohm=1V. But what happens if you give it a 2 Ohm load? It will do whatever it has to do to force 1A through the load. In this case, it will develop 2V of output. 1A*2 Ohms=2V. An ideal current source could develop 1kV across a 1k resistor, simply because you told it to deliver 1A, no matter what.
Naturally, real current regulators have limitations, just as voltage regulators do. They can only deliver current up to a certain voltage, after which they run out of steam.
It's all a matter of perspective. Think of a current regulator (aka current source) as an "upside down" voltage regulator and all will be clear.

Grey

[Cloth Ears]

Originally posted by Zen Mod
just download ( if you aren't already ) all zen articles and read them.
after that ,shoot with questions

Zen Mod, I think that after 43 years of only building passive circuits (x-overs) that my intuitive understanding of what a FET or bp transistor does, or what an active circuit does, is just not what it should be. Take this bit from the original Zen article on the current source:

Dealing first with the current source, we note the circuitry associated with Q2. Q3 is used to regulate the gate drive for Q2. It is fed current (biased) by R6/R7, with C5 used to filter out power supply ripple. As current passes through Q2, it develops a voltage drop across R1, and when this voltage drop reaches about .66 volts (2 amps through Q2/R1), it turns on the junction of Q3, and Q3 then limits the voltage appearing at the gate of Q2 to about 4 volts. This little loop operates to keep the current through Q2 at a constant 2 amps. R3 and R4 are there to add stability to the loop and prevent parasitic oscillation of the Mosfet Q2.

OK, I understand that 2 amps through the .33ohm R1 is a voltage drop of .66V - but why does that turn on the junction of the Q3 (is that just how the MPSA92 works)? And why does Q3 limit the voltage appearing at the gate of Q2 to 4V? It seems like a water-flow system, where the water is flowing through Q2, but when it reaches a certain cfm rate, another element (Q3 - like a tap, maybe) comes into play that ensures that only a certain amount goes through Q2.

The problem is that I'm still in kindergarden, and you guys (even dumbing it down for me) are still talking at high-school level.

Originally posted by Nelson Pass
The latest copy of AudioXpress has a great article on current
sources written by Walt Jung. Lesser examples can be found
in pieces at www.passdiy.com

Nelson, now I'm really embarrassed. I've read all the articles from A40 to ZV9 - some of which are still over my head, and some like SOZ which are almost completely understood by my little grey cells. "Lesser examples" indeed!

Originally posted by GRollins
You're familiar with the idea of a voltage regulator, right? ...

Grey, thank you. I am familiar with the idea, and could follow your post. And, I can understand that the current source from Zen would deliver what it says it will. I think I need to look for some tutorial on the Internet (and there must be one out there) that will explain why these transisters do what they do. And how.

I'm pretty sure I could get some parts together and copy what someone else has already done. But I'm not really into "monkey see, monkey do" - so even if I do copy someone's work, I'd like to know why I'm doing it.

I'll come back to this when I know a bit more about what questions to ask. When? Well, hopefully before "..., the sun will cool to a white dwarf, and after that the universe will experience heat death."

[Zen Mod]

Originally posted by Cloth Ears

................

are you on broadband?


if yes-mail me and I'll shoot you with few forbidden books

[Cloth Ears]

Zen mod - 2 mails sent. The second contains my (unlimited) email address. I think hotmail is limited to 2Mb.

[GRollins]

The thing to note about current sources is that the control element (grid/base/Gate) is held constant. As such, the pass device isn't amplifying a signal, it's passing a steady current.
It's just a question of sitting down and staring at it for a while.

Grey

[jupiterjune]

It seems like a water-flow system, where the water is flowing through Q2, but when it reaches a certain cfm rate, another element (Q3 - like a tap, maybe) comes into play that ensures that only a certain amount goes through Q2

Actually, pretty much every part has an analogous water flow system part. A mosfet is like a valve - with a "check valve" (backflow preventing valve) attached to one side of it. The mosfet gate is analagous to the valve handle, which turns your flow on and off.
Voltage is pressure, amperage is the water flow rate. The mathematical equations for the two systems are largely identical.

I found the DIY op amps article to be quite helpful in describing exactly how that current source works. For bipolar transistors, the .65 volts is a constant, it is the voltage gate to source required to turn the device on.
As long as you are willing to do a lot of reading, and ask questions, you will get this stuff no problem. But don't hesitate to build some of this stuff even though you don't understand everything that is going on -- you will probably learn a lot more if you build some simple circuits and look at what is going on with them--via a DC meter and an oscilloscope if you can get your hands on one. I can only learn so much by just reading.

JJ

[RoboMan]

Originally posted by Cloth Ears


OK, I understand that 2 amps through the .33ohm R1 is a voltage drop of .66V - but why does that turn on the junction of the Q3 (is that just how the MPSA92 works)? And why does Q3 limit the voltage appearing at the gate of Q2 to 4V? It seems like a water-flow system, where the water is flowing through Q2, but when it reaches a certain cfm rate, another element (Q3 - like a tap, maybe) comes into play that ensures that only a certain amount goes through Q2.

Agree that you shouldn't just build it without knowing how does it work. You will not be able to do troubleshooting without a thorough understanding.

Let me try to answer your question:
As you may already know that a diode will start conduct when a forward voltage of 0.66 voltage is applied to it. The B-E junction of Q3 acts like a diode. When the voltage across B-E of Q3 gets to about 0.66V, then current start to flow through the B-E junction and the current is amplified and causes a current between C-E. Since the current at C of Q3 is supplied from two fixed resistors R11 and R12, if current passes through Q3, the voltage will drop. When the voltage drops, the gate voltage of Q2 will also drop, current passing through Q2 will drop too, so does the current passing through R1. This will cause Q3 to conduct less current in turn. So Q3 is keeping the DC current of Q2 to a constant level. The value of R1 will determine the current of Q2. The voltage across R1 is always 0.66V. The current of Q2 is equal to 0.66V / R1.

(The part no. are based on Zen-V4.pdf)

I would say that this forum is better than any book can supply. Feel free to list your questions here. (That will also benefit other people who are too shy to ask.)