Message 29140 in TECH.WW
From: G8MNY
Date: Tue, 01 Sep 26 06:52:00 Z
Newsgroups: TECH.WW
Subject: Darlington & Quasi Darlington
Message-ID: <3868_GB7CIP>
Path: N2MH4|GB7BED|EI2GYB|GB7CIP
R:260901/0653Z 36407@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260901/0653Z 16860@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260901/0652Z 58368@EI2GYB.DGL.IRL.EURO LinBPQ6.0.25
R:260901/0652Z @:GB7CIP.#32.GBR.EURO #:3868 [Caterham Surrey GBR] $:3868_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated May 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This simple way to improve the current gain of a transistor just use 2 in
cascade, often used in PSUs & AF output stages and even the odd RF signal amp.
Two separate devices can be used or in a single package.
NORMAL Collector
Emitter
This method has the 2 transistors of the same type, and has the disadvantage of
higher bias voltage.
This is often used where T1 is a PNP & T2 is a cheaper high power NPN.
To speed up the 2nd transistor turn off, a low R is often used base to emitter
in either configuration.
AS USED IN A PUSH PULL AMP
DARLINGTON 3A
CLASS A STAGE QUASI COMPLIMENT ZOBAL LOAD
COMPONENT VALUES
Input Z = Rin, e.g. 10K
XCin = Rin @ 10Hz, e.g. 2uF
Rb sets 35V on output, ((Rc+Rs) x T1Hfe), e.g. 330K
Gain = (Rnfb//Rb)/Rin, e.g. 10x = 150K
XCnfb = Rnfb @ < 10Hz, e.g. 1uF
T1= 100mA 100V 100x 1W NPN device
T2 & T3 = 1A 100V 30x 5W, e.g. TIP30 PNP & TIP29 NPN
T4 & T5 = 15A 100V 20x 115W on heatsink, e.g. 2N3055
100R in T4 & 5 base-emitter, ensure they turn off properly.
D1 & D2 drop the 1.3V needed to just under bias outputs, e.g. 1N4148
Re maintain thermal stability, e.g. 0R22 2W
Rc sets the peak +ve output current (e.g.1/2 x LS x T5Hfe x T3Hfe) e.g. 2K2 2W
Cbs & Rbs make a bootstrap to maintain current through Rc.
Rbs = Rc/2 e.g. 1K 1W
XCbs = Rbs @ < 10Hz e.g. 30uF @ 50V
XCls = LS @ < 10Hz e.g. 1000uF @ 50V
XCpower = LS @ < 20Hz, assuming 100Hz supply from bridge, e.g. 4700uF @ 80V
Zobal network keeps the output terminated at HF when the LS is open circuit,
for stability.
In practice there would be more gain stages in front providing 3V RMS drive and
more N.F.B. for lower overall distortion, but this circuit should work OK.
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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