Sziklai configuration complementary Darlington transistor

[Winfield Hill]

Group: sci.electronics.design
Title: Re: amplifiers with flywheel diode protection
Author: Winfield Hill <[email protected]>
Date: 5 Feb 2004 16:04:33 -0800

Winfield Hill wrote...

Jim Thompson wrote...

[ with reference to the circuit-designation in H&H AoE page 95. ]
Win, Do you have a reference for first use of "Sziklai pairs"?

Your recent postings were the first I'd heard that the
configuration had a name.

Sziklai was an early consumer TV-receiver-circuits pioneer.
http://216.239.53.104/search?q=cach...cial_sect/people3.html+Sziklai&hl=en&ie=UTF-8

He filed a patent for the first complementary-output amplifiers
in 1953, # 2,762,870, granted in 1956. Also # 2,791,644 filed
in 1952. These are for the usual complementary push-pull
amplifier output stages that we're all familiar with.

Here's a site where H. C. Lin tells the story of his invention
of the quasi-complementary amplifier output stage for CBS in the
mid 50s. He says he invented it because they didn't have good
germanium NPN power transistors, so they couldn't use Sziklai's
usual circuit. He filed for a patent on this push-pull amplifier
May 3, 1955 (# 2,896,029 issued July 21, 1959) and also wrote an
article which appeared in Electronics, v 29, pp 173-175, Sept 1956.
http://www.semiconductormuseum.com/Transistors/RCA/OralHistories/Lin

Lin's 1955 quasi-complementary push-pull amplifier contains within
it a complementary Darlington (see page 7 of the web pages above),
but his patent cites only the full push-pull amplifier. He does
reference two 1953 Sziklai articles from Electronics Engineering
and Proc. of the I.R.E. Hmm, I'll need to read those next.

It's nice to have a real name, not just "complementary Darlington,"
but now I wonder if using Sziklai's name is proper. It's certainly
rather widely used. Gotta go read those 1953 Sziklai articles.

OK, reporting back, having read those old articles.

George C. Sziklai was indeed the first to report the complementary
Darlington configuration that now bears his name, in a lecture to
the Royal Society of Arts, "Transistor Circuits and Applications,"
in London on July 1, 1953. The text and illustrations of his talk
comprise a 7-page article in Electronic Engineering, Sept 1953,
p358-364. There's a different, slightly more detailed article,
"Symmetrical Properties of Transistors and Their Applications,"
Proc IRE 41, 717-724 (1953), where he repeats the circuit, saying
it operates with dc feedback. "The low output impedance and the
stable operation is made possible by the over-all feedback which
extends down to dc. This feedback was suggested by R.D. Lohman."
I'm not sure what that means, did Lohman suggest the circuit?

| ,--o---------,
| |/V | +
| ,---| _-_
| |/ |\ _-_
| ,---| | |
| | |\V | |
| ---o--+ |-----+--o SPKR ---+
| | |/V | |
| '---| | | +
| |\ |/ _-_
| '---| _-_
| |\V |
| '--o---------'

I've turned Sziklai's drawing upside-down because these days
we like the + voltage at the top of our drawings. The circles
show the four terminals of a four-transistor plastic 1/2-watt
amplifier module they made, which looks just like a vacuum tube.

There was no class-AB bias, so it must have sounded terrible.
Maybe that's why Sziklai didn't patent this circuit, although
he applied for patents on several much more simple and not as
useful circuits the same year. Sziklai noted that the circuit
drew zero quiescent current. Push-pull biasing concepts came
along a year or so later...

Here's H. C. Lin's circuit, which he patented for RCA several
years later. It was intended to get around the fact that in
the 50's they didn't have good NPN germanium power transistors.

He used a regular Darlington, plus a Sziklai on the other side.

| ,-----------,
| |/V | +
| ,---| _-_
| |/ |\ _-_
| ,---| | |
| | |\V | |
| -----+ |-----+-- SPKR ---+
| | | |
| 100 |/V | +
| ohms ,---| _-_
| | |/V |\ _-_
| +---| | |
| | |\ | |
| bootstrap '-----+-----------'
| circuit

(Although he uses Sziklai's configuration for an important half
of the circuit, he doesn't reference Sziklai's earlier articles,
but he references a few other 1956 articles that should be read.)

BTW, back in those days they didn't yet call two-transistor emitter
followers Darlingtons, nor does the phrase emitter follower appear
in the three articles I have written by these two famous engineers.

These are valuable old articles that should be in among today's
literature, so I'll scan and post them in an accessible place.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[N. Thornton]

George C. Sziklai was indeed the first to report the complementary
Darlington configuration that now bears his name, in a lecture to
the Royal Society of Arts, "Transistor Circuits and Applications,"
in London on July 1, 1953. The text and illustrations of his talk
comprise a 7-page article in Electronic Engineering, Sept 1953,
p358-364. There's a different, slightly more detailed article,
"Symmetrical Properties of Transistors and Their Applications,"
Proc IRE 41, 717-724 (1953), where he repeats the circuit, saying
it operates with dc feedback. "The low output impedance and the
stable operation is made possible by the over-all feedback which
extends down to dc. This feedback was suggested by R.D. Lohman."
I'm not sure what that means, did Lohman suggest the circuit?

| ,--o---------,
| |/V | +
| ,---| _-_
| |/ |\ _-_
| ,---| | |
| | |\V | |
| ---o--+ |-----+--o SPKR ---+
| | |/V | |
| '---| | | +
| |\ |/ _-_
| '---| _-_
| |\V |
| '--o---------'

I've turned Sziklai's drawing upside-down because these days
we like the + voltage at the top of our drawings. The circles
show the four terminals of a four-transistor plastic 1/2-watt
amplifier module they made, which looks just like a vacuum tube.

There was no class-AB bias, so it must have sounded terrible.

Was it for audio? Presumably they would have added some overall nfb.
Note that true class B was normal in the 50s for cost reasons, so such
circuits had a market, primarily for announcement PA systems and other
low quality jobs. Even old tape recorders sometimes had class B
output.


Regards, NT

 

[Jim Thompson]

On 5 Feb 2004 20:00:02 -0800, Winfield Hill

Sziklai was an early consumer TV-receiver-circuits pioneer.
http://216.239.53.104/search?q=cach...cial_sect/people3.html+Sziklai&hl=en&ie=UTF-8

He filed a patent for the first complementary-output amplifiers
in 1953, # 2,762,870, granted in 1956. Also # 2,791,644 filed
in 1952. These are for the usual complementary push-pull
amplifier output stages that we're all familiar with.

[snip]

| ,--o---------,
| |/V | +
| ,---| _-_
| |/ |\ _-_
| ,---| | |
| | |\V | |
| ---o--+ |-----+--o SPKR ---+
| | |/V | |
| '---| | | +
| |\ |/ _-_
| '---| _-_
| |\V |
| '--o---------'

[snip]

The version I did at Motorola had voltage gain:

,--o---------,
|/V | +
,------------------| _-_
|/ |\ _-_
,---| | |
| |\V | |
---o--+ |-----o----/\/\/\----+--o SPKR ---+
| |/V | R2 | |
'---| \ | | +
|\ R1 / |/ _-_
| \ o-------| _-_
| / | |\V |
| | | '--o---------'
o----(-----o
|
GND

since the driving chip could only swing to within 1.4V of rail.

...Jim Thompson

 

[Tom Del Rosso]

In Winfield Hill typed:

Jim Thompson wrote...

[ with reference to the circuit-designation in H&H AoE page 95. ]
Win, Do you have a reference for first use of "Sziklai pairs"?

"A small resistor from base to emitter of Q2 is advisable." That should
read "collector", no?

 

[Winfield Hill]

Tom Del Rosso wrote...

[ with reference to the circuit, fig 2.62 in H&H AoE page 95. ]

"A small resistor from base to emitter of Q2 is advisable."
That should read "collector", no?

No! The output transistor needs a base-charge-drain pathway to
improve high-frequency performance (and high temperature, too).
This is true for both Darlington and Sziklai transistor pairs.
The resistors establish a minimum operating current for input
transistors Q1 Q3 and a base-leakage-current pathway for the
output transistors Q2 Q4, which must have been doubly important
in the 50's with hot germanium power transistors.

| ,-----+------------,
| R | |
| | |/V | +
| +---| Q2 _-_
| |/ |\ _-_
| ,---| Q1 | | 20V
| | |\V | |
| | | | 16-ohm |
| -----+ +-----+--+- SPKR --+
| | | | | |
| | R | | |
| 100 | |/V | | +
| ohms +---| Q4 | _-_
| | |/V |\ | _-_
| +---| Q3 | | | 20V
| | |\ | | |
| | | | | |
| 2.7k '-----+--| --+-----'
| | 50uF | |
| +----||--------' |
| | bootstrap |
| 1.0k |
| '------------------'

They had learned this by 1955 or so, and all five resistors
shown above were in the output stage of H.C. Lin's amplifier.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Tom Del Rosso]

In Winfield Hill typed:

Tom Del Rosso wrote...

[ with reference to the circuit, fig 2.62 in H&H AoE page 95. ]

"A small resistor from base to emitter of Q2 is advisable."
That should read "collector", no?

No! The output transistor needs a base-charge-drain pathway to
improve high-frequency performance (and high temperature, too).
This is true for both Darlington and Sziklai transistor pairs.

Now I see what happened! The diagram 2.62 has "C" above the output
emitter, meaning that it's the collector of the combined pair, and "E"
below. I didn't look too carefully.