Various Transistors Tested for Ic and Vce(sat)

side

Circuit description:

Yes, I read that. I didn't realize that the saturation voltage could be that high, and I always considered it to be a limiting parameter, rather than an operating parameter. I went scurrying back to my textbooks and refreshed myself on how Vs varies with the Ic/Ib ratio. Apparently that is the clue here. As the collector current increases, assuming a fixed supply voltage, the circuit current ratio changes causing Vsat to rise.

I'm still not impressed, eben though the circuit appears to work.

R2 wastes a lot of power.

John

Never did like those aluminum jobbies. All my K&E ever needed was a little talc on the slides periodically.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Real men use a yellow Pickett.

John

My superficial observation is that the inductor is charged up to the 2.4 mA base current of Q2 times its beta, and the whole thing is dumped into the LED. I may not know enough to design a good one, but just that much is enough to see this is a bad one.

I also see what you mean about duty cycle, but I can't compute it.

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You are the first person to note that the device comes out of saturation based upon *BETA*! *NOT* the saturation rating of the transistor!

Congratulations!

I tried to give Watson some measurement hints, but he ignored them, citing Electronic Design as the "authority"... ROTFLMAO!

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Here is the circuit explanation from their website

"The circuit description is cyclical, meaning there's a series of events that loops back on itself. The cycle starts with the battery voltage slightly above Q2's VBE. This creates a positive Q2 base current: iB = (battery voltage ? VBE)/R2

and Q2 turns on, thus switching inductor L1 to ground. Q1 is off. Energy stored within L1's magnetic field builds as L1's current rises with a positive di/dt. As this current rises, it also flows through Q2's RSAT (D1 is off). Q2's collector voltage becomes sufficiently large to turn on Q1. Q1's base voltage is connected to Q2's collector by the feed-forward network of R1 and C1. R1 also serves as Q1's base current limit.

As Q1 turns on, the previous base drive to Q2 is then shunted to ground and Q2 turns off. The switching off of Q2 discharges L1's energy into the LED (D1) as the magnetic field collapses. This flyback action of L1 forward-biases D1, which gives up photon illumination in the form of white light. With L1 discharged, Q1 turns back off. The self-oscillating action repeats until the battery voltage falls below Q2's VBE.

L1, Q2's RSAT, and the switching characteristics of Q1 and Q2 dominate the period and duty cycle of this oscillation. LED brightness depends directly on the average current flow through D1. D1 is on while Q2 is off and off while Q2 is on.

The oscilloscope waveforms

show the battery current, D1 current, and D1 voltage during the switching period of 10.8 µs (93 kHz). With a 1.0-V battery voltage, the average battery current is 41 mA, and the average LED current is 14 mA. Using a Coilcraft DO1608-104 inductor and a Nichia BSPW500BS LED, the nominal input/output power efficiency is 23%, 34%, and 72% with a battery voltage of 0.8 V, 1.0 V, and

1.5 V, respectively."

But a lot more is wasted through Q2, right? Looking at Fig 2 (graphs) you can see that most of the integral of the supply current is during the period when the LED is off. The text admits that the efficiency is

34% with a 1 volt supply.

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Marvelous! "...the battery voltage falls below Q2's VBE"... ROTFLMAO!

Tom Del Rosso properly pointed out that BETA is a key element.

All phases of this oscillator ARE CALCULABLE. Please attempt to do so instead of giving a hand-waving re-description of the nonsense in the Electronic Design article. For instance, please write out...

Tsat = f(beta, Vcc, L, RL, rsat, etc.)

Likewise...

Toff = g(beta, Vcc, L, RL, rsat, etc.)

BTW, the *only* restraint on battery voltage is that is must be less than the VF of the LED. The ED article is just plain BS!

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I must have stumbled into the truth then. :)

I used to badger Win about putting more analysis into AoE instead of lots of example circuits (and what he describes as "bad circuits" also) that come with no analysis at all. I'm not sure, but I think he KF'ed me. (When he responds to me it's always via answering another responder.) Maybe it was because of politics though.

Pease and Frederickson books offer more insight, but I've only started on them. I spend too much time reading here.

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I read in alt.binaries.schematics.electronic that Watson A. Name - Watt Sun, Dark Remover wrote (in ) about 'Various Transistors Tested for Ic and Vce(sat)', on Sun, 4 Jan 2004:

I don't find it any problem with this EF76 I have here.

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I read in alt.binaries.schematics.electronic that Jim Thompson wrote (in ) about 'Various Transistors Tested for Ic and Vce(sat)', on Sun, 4 Jan 2004:

Moisture from damping resistors gets into the package. This often makes the transistor permanently saturated, as you can tell by Vce being very nearby zero under all conditions.

When it gets hot enough to evaporate the moisture.

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I read in alt.binaries.schematics.electronic that John Larkin wrote (in ) about 'Various Transistors Tested for Ic and Vce(sat)', on Sun, 4 Jan 2004:

Use a 0.1 W type, then.

-- Regards, John Woodgate, OOO - Own Opinions Only.

Interested in professional sound reinforcement and distribution? Then go to PLEASE do NOT copy news posts to me by E-MAIL!

No, I don't consider it stumbling to notice that the collector current has to less-than or equal-to beta*Ib... sort of a fundamental observation!

Win is a *collector* of circuits... there really is *no* analysis in AoE.

Hey! That's an honor, you've been KF'd by a leftist wienie! (I just love yanking Win's chain ;-)

Tom Frederiksen (note the spelling) and I shared a cubicle at Motorola in the early '60's. We both learned a lot by critiquing each other's circuits. And a lot of crazy coffee bets... I came up with the MC1554 all-NPN output stage on a coffee bet, also the composite lateral-PNP-NPN scheme (posted on a.b.s.e previously) which gave us predictable-performing lateral PNP's.

I'm referenced in Tom's OpAmp book on page 14.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

2.4

into

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network

and

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directly

µs

and

At least they're consistent...a BS explanation for a BS circuit! Purrrfect! I can't even get the simulation to work :-(

[snip]

Make sure you have some resistance in the inductor. Depending on simulator, you may need an initial-condition statement.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

"Baphomet" schreef in bericht news: snipped-for-privacy@corp.supernews.com...

Purrrfect!

It simulates fine here. Start with 0V from the battery. I don't find it a bad circuit, considering the low part count etc.

The average current through the LED isn't that bad either, given the duty-cycle.

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Thanks, Frank.
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Or an RK5744 or 5703. :)

Tim

-- "That's for the courts to decide." - Homer Simpson Website @