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G8MNY > TECH 11.03.08 03:00l 85 Lines 3612 Bytes #999 (0) @ WW
BID : 49706_GB7CIP
Read: GUEST
Subj: Darlington & Quasi Darlington
Path: IZ3LSV<IW2OHX<OE6XPE<DB0RES<ON0AR<GB7CIP
Sent: 080311/0003Z @:GB7CIP.#32.GBR.EU #:49706 [Caterham] $:49706_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)
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 O/P terminated at HF when the LS is O/C, 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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