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I'm not that current on the latest opamps. But I use a lot of OPA134's (mostly dual 2134's) 20V/us slew rate. But a 'tad' more expensive than a LM358.
What about a standard push-pull to save power.... or class D? (I never done a class D thing.)
George H.
You could call it "Output stage that oscillates fiercely with no load, and melts transistors rapidly" ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
This circuit is very poorly designed.
I wouldn't even punch this circuit into a machine to simulate it, it is obviously so bad.
One thing that stands out right away is that it runs off a single supply and generates reference voltages using unbypassed voltage dividers, which is a naive practice that begs for oscillation.
The flipped-about push-pull arrangement seems not to be operating the transistors near cutoff like a conventional push-pull design, which is the main idea behind class AB.
I haven't done the calculations, but at a glance, I can tell this thing will have a lot of current flowing through the transistors at quiescence.
I wouldn't even bother thinking about cross-over distortion. That can't be a factor here, because it doesn't look like the transistors are not going to be cut off simultaneously.
For instance if we look at Q2, you have half the supply voltage dropping through a 560/120 divider providing the base bias. This is likely enough to turn on the transistor, given enough supply voltage and the same thing is happening in the upper half, which is a PNP mirror-image. Resistor R11 provides only very modest feedback to limit the current because it is small.
Let's assume a supply of 12, so the midpoint is 6V. 120/560 * 6 gives us
1.3V. This is way above VBE so transistor will turn on. We can estimate maximum collector current using (1.3V - 0.7V)/0.2 Ohms = 3A (!). There isn't nearly enough current-limiting by the tiny emitter resistors.
OSOF or OSOF-MT ?
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OK that was a silly idea. (Two pass elements is not going to save any power.)
(It isn't any fun to google before posting... :^) So a sliding class A is also called class H? A variable (switch mode) power supply rail run a volt or two above the linear pass element.
That's a pretty cool!
So how fast can you oscillate a SMPS and how fast can you swing it's output voltage?
George H.
=A0 =A0 ...Jim Thompson
=A0 =A0| =A0 =A0mens =A0 =A0 |
=A0 | =A0 =A0 et =A0 =A0 =A0|
=A0|
=A0 =A0 =A0 =A0 |
|Hide quoted text -
The gain is set with the two 2K resistors and the 10K for a gain of
There is cross-over distortion which doesn't seem to be related to the bias current since I ran the supply voltage up to increase the bias current with no effect on distortion.
The tiny resistors are only there to measure the bias current. Thermal stability is another problem.
-Bill
Indeed, that looks like what the circuit is shooting for.
I found a this schematic which has a similar configuration of transistors as the OP's circuit, also single supply, but seems better:
Here, a pair of diodes and resistor R5 are used to set up the collector current through the transistors, instead of a resistive voltage divider bias. Since diodes are used, there is independence from fluctuations in the rails. R5 at
39 ohms is much larger than the 0.2 ohm emitter resistors in the circuit discussed in this thread, so the quiescent current is kept to about 18 mA. (Approximation: 1.4V diode stack minus 0.7 forward voltage, divided by 39 ohms).The OP's circuit could be improved by adopting some of these ideas, and also with the addition of some bypass caps on those voltage dividers around the op amp.
t -
Grin... maybe a good heater then.
Bill, I hope you'll take this as good natured kidding. We all make mistakes.
(I can only learn by making mistakes, so the faster I make 'em the more I know.)
When I've got something new to design, I like to think of a bunch of ways to solve the problem. Then if you try a hair-brained one and it fails, you've got something to fall back on.
George H.
[snip]
Google or Wiki are not always reliable sources of information.
Check out...
as one way I've done it.
Normal class-A has one active signal device loaded with resistance or a fixed current mirror of value I. Say your supplies are +V and -V, load to ground. So the peak power that can be driven into the load is I*V. Quiescent power 2*I*V.
Now imagine a current mirror load whose value decreases when the active signal device increases its current (and vice versa). Say the quiescent condition is the same as above. But now you can drive peak power of 2*I*V, twice what the normal class-A can do. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
While you are amusing yourself, what is it that determines the output Q-point... quiescent voltage at the + node of C3 ?:-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
current
Looks like R3 should go to the output node. It doesn't make any sense being where it is now. Then DC feedback would make the output sit at about 5 volts, which would be about right for a symmetric swing given the compliance of the upper current source. I also don't know why R3 is connected where it is, it would make more sense connected to the top of R1. I think you'd then have a pretty conventional, but workable amplifier.
current
Too many parts ;-)
What kind of gain is needed? Likewise, what impedance are the headphones? ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
hown
about a
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ok good
rsion
Woah... Some reading material! great.
Yeah I've done plenty of class A.... brute force. Add more voltage and resistance and I can drive that coil faster.
Dang, I've only done one current mirror... doing circuits out of AoE. just a few transitors, stuck into white proto board.
That's OK I'll never run out of circuits to try, or novels to read.
Now I've got some nice hearing aid app note to read... Grin
George H.
=A0 =A0 ...Jim Thompson
=A0 =A0| =A0 =A0mens =A0 =A0 |
=A0 | =A0 =A0 et =A0 =A0 =A0|
=A0|
=A0 =A0 =A0 |
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"Kaz Kylheku" Phil Allison
** Like hell - that has a CCS as half the output stage.The OP's schem is like a donkey with a dog's head.
... Phil
I only made one mistake. That was the time I thought I made a mistake.
-Bill
I would love nothing more than to view that jpg however, It seems that site is so loaded with Flash content and scam ads that It just wants to cover all of my screen with pop up forms all over the place.
You see, I need to click on the actual image to see it properly because it is not sized correctly for view and they know this. You click on it, which normally brings up the image in fall details but, it also starts a whole crap load of other scams, ads and forms to pop up all over.
These free sites in my opinion, are worthless if you really want some one to see the content. They are just lures to get more people to see their useless ads, take advantage of poeple and in many cases makes your PC useless when you're trying to shut down the forms as they keep starting as they attempt to install shopping tool bars and all the other crap.
Just my opinion. These Free sites are nothing but bone yard traps.
You know, most providers of services (ISP)'s provide their customers with a personal webpage or webspace of more than enough with a clean slab to start with.
Jamie
Do this...
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I don 't understand why you don't see it in the sim?
I see all kinds of problems there.
THe outputs are current modes and the beta on the outputs are most likely are not going to match well.
On top of that, LTspice shows the upper output (PNP) going into discontinue state at the cross over. This is going to give you a period of what I call a flat liner and 99% sure this is where your cross over error is coming from.
Plot the current on R12.
Jamie
.
ome
Yeah sorry, It seems to have gotten much worse.
Got a better image hosting site? I tries this tinyurl one. But it wanted me to enter a security code for each image.
I suppose I could try and set up a web page.... Yola?
George H.
I didn't notice.
Ah that's right, I run the NoScript blocker available for Firefox. NoScript identifies all the sites which, for the given page, are being used as sources of JavaScript code. You can individually add them to the good list.
What ads? Adblock! I absolutely do not see a single ad or popup on this site. Just text, a few buttons like "Sign Up" (That one is scripted: clicking on it works) and the image.
Your fault for not getting a clue about what browsers can do for you.
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