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G8MNY > TECH 27.02.05 17:02l 81 Lines 3242 Bytes #999 (0) @ WW
BID : 34401_GB7CIP
Read: GUEST
Subj: Darlington & Quasi Darlington
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0NOS<DB0BI<DB0PRA<DB0LJ<DB0RES<ON0AR<
7M3TJZ<HG8LXL<CX2SA<GB7YFS<GB7WSX<GB7CIP
Sent: 050227/1121Z @:GB7CIP.#32.GBR.EU #:34401 [Caterham] $:34401_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Dec 04)
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
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!
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 PUSH PULL AMP
DARLINGTON 3A
Quasi ÚÄÄÄÂÄRbsÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄo-oÄÄÄÂÄÄÄÄ<+70v
Complementary ³ Rc ³/ T3 ³ Fuse ³ From Bridge
Output ³ ÃÄÄÄÄÄ´ NPN ³ + ³
=== ³ 6mA ³\e ³/ T5 ===
Cbs³ _³_ ÃÄÄÄÄ´ NPN Cpower ³
³ \_/ D1 ³ .2A³\e ³
³ ³Bias 100 ³ ³
³ ³ ³ Re 4A Pk ³
ÚÄÄÂÁÄÄÄ)ÄÄÄÄÄÄÄÁÄÄÄÄÄÄÅÄÄÄÄÂÄÄÄÄ¿ ³
Rnfb ³ _³_ D2 Re ³u1 ³+ ³
³+ ³ \_/ ÚÄÄÄÄÄÄ´ === === Cls ³
=== ³ ³ ³/e T2 ³ ³ ³ ³
Cnfb³ Rb ÃÄÄÄÄÄ´ PNP ³ ³ ÚÁ¿/³LS ³
AF ³ ³ ³/ ³\ ³/ T4 8ê ÀÂÙ\³8ê ³
Input >ÄÄRinÄ´ÃÄÁÄÄÁÄÄ´NPN ÃÄÄÄÄ´ NPN ³ ³ 60w ³
Cin T1 ³\e 100 ³\e ³ ³ ³
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄ<0v
QUASI Zobal
VALUES
Input Z = Rin, eg. 10K
XCin = Rin @ 10Hz, eg. 2uF
Gain = (Rnfb//Rb)/Rin, eg. 10x = 150K
XCnfb = Rnfb @ < 10Hz, eg. 1u
T1= 100mA 100v 100x 100mW
T2 & T3 = 1A 100v 30x 5W, eg. TIP29/30
T4 & T5 = 15A 100v 20x 115W on heatsink, eg. 2N3055
D1 & D2 drop the 1.3V needed to just under bias the O/Ps, eg. 1N4148
Re maintain thermal stability, eg 0.22ê 2W
Rb sets 35V on O/P, ((Rc+Rs) x T1Hfe), eg. 330K
Rc sets the peak +ve O/P current (eg « x LS x T5Hfe x T3Hfe) eg. 3K3 1W
Cbs & Rbs are bootstrap to maintain current through Rc. Rbs = Rc/2 eg 1K5 0.5W
XCbs = RS @ < 10Hz eg. 20uF @ 50v
XCls = LS @ < 10Hz eg. 1000uF @ 50v
XCpower = LS @ < 20Hz assuming 100Hz supply from bridge, eg 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 & more N.F.B. but this
circuit should work OK.
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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