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G8MNY > TECH 22.08.10 09:01l 87 Lines 3640 Bytes #999 (0) @ WW
BID : 60339_GB7CIP
Read: GUEST
Subj: Darlington & Quasi Darlington
Path: IZ3LSV<IK2XDE<DB0RES<ON0AR<UA6ADV<GB7CIP
Sent: 100822/0110Z @:GB7CIP.#32.GBR.EU #:60339 [Caterham] $:60339_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
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 & even the odd RF signal amp.
Two separate devices can be used or in a single package.
NORMAL Collector
DARLINGTON ÚÄÄÄÄ´ /|\
T1 ³/ ³ |
Base ÄÄÄÄÄ´ ³ 1V Current
/|\ ³\e ³/ Saturated Gain HFE = T1 x T2
| ÀÄÄ´ T2 |
1-1.5V ³\e |
À - - -> ³ \|/
Emitter
This method has the 2 transistors of the same type, & has the disadvantage of
higher bias voltage.
QUASI ³ Collector!
DARLINGTON ³/e /|\
NPN ÚÄÄ´ T2 |
T1 ³/ ³\ PNP 1V
Base ÄÄÄÄÄÄ´ ³ Saturated Gain HFE = T1 x T2
/|\ ³\e ³ |
0.6V ÀÄÄÄÄ´ \|/
À - - -> ³ Emitter
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 ê is often used base to emitter
in either configuration.
AS USED IN A PUSH PULL AMP
DARLINGTON 3A
Quasi ÚÄÄÄÄÂÄÄRbsÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄo-oÄÄÄÄÄÄÂÄÄÄÄ<+70V
Complementary ³ Rc ³/ T3 ³ Fuse ³ From Bridge
Class B Output ³ ÃÄÄÄÄÄÄ´ NPN ³ +³ Rectifier
=== ³ 6mA ³\e ³/ T5 ===
Cbs³ _³_ ÃÄÄÄÄÄÄ´ NPN Cpower³ e.g. 50V @ 2A
³ \_/ D1 ³ .2A³\e ³ transformer
³ ³Bias 100ê ³ ³
³ ³ ³ Re 4A Pk ³
ÚÄÄÂÁÄÄÄÄ)ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÂÄÄÄÄÄ¿ ³
Rnfb ³ _³_ D2 Re ³u1 ³+ ³
³+ ³ \_/ ÚÄÄÄÄÄÄÄÄ´ === === Cls ³
=== ³ ³ ³/e T2 ³ ³ ³ ³
Cnfb³ Rb ÃÄÄÄÄÄÄ´ PNP ³ ³ ÚÁ¿/³LS ³
³ ³ ³/ ³\ ³/ T4 8ê ÀÂÙ\³8ê ³
AF>ÄÄRinÄ´ÃÄÁÄÄÁÄÄÄ´NPN ÃÄÄÄÄÄÄ´ NPN 1W ³ 50W RMS ³
Input Cin T1 ³\e 100ê ³\e ³ ³ ³
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÄ<0v
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. TIP29/30
T4 & T5 = 15A 100V 20x 115W on heatsink, e.g. 2N3055
100ê 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. 0.22ê 2W
Rc sets the peak +ve output current (e.g. « 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 &
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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