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G8MNY > TECH 08.01.06 00:15l 87 Lines 3275 Bytes #999 (0) @ WW
BID : 12161_GB7CIP
Read: OE5RCO OE7HNT DL1LCA DJ9UI GUEST OE7FMI
Subj: Adjusting 78xx/79xx Regulators
Path: DB0FHN<DB0FOR<DB0SIF<DB0BID<DB0EAM<DB0SMG<DB0RES<ON0AR<GB7YKS<GB7PZT<
GB7YFS<GB7CIP
Sent: 060107/2259Z @:GB7CIP.#32.GBR.EU #:12161 [Caterham] $:12161_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Feb 05)
There are 3 way to simply increase the regulator voltage.
1/ Add a series zener or diodes or a mixture in the common leg. Most makes of
regulator put about 50uA down the common leg, this may affect the zener/diode
drop. A pull up R of a few Kê from the zener to the output could be needed with
slightly leaky zeners/diode to get the desired drop.
in ÚÄÄÄÄÄÄÄ¿out
+12V >ÄÄÄÄÄÄÂÄÄÄÄ´ 7805 ÃÄÄÄÄÄÂÄÄÄ> +8V
RAW DC ³ ÀÄÄÄÂÄÄÄÙ ³
FROM >2200uF ³+ comÃ Ä ÄRÄ Ä ´
BRIDGE 16V === _³_ ³
RECTIFIER ³ /_\` 3v === 0.1u
& 10V AC ³ ³ ³
0V >ÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄ>
Thermal stability fair, as it is dependent on Reg + Zener, 3 Ä 5V zeners
generally have the best stability!
in ÚÄÄÄÄÄÄÄ¿out
+12V >ÄÄÄÄÄÂÄÄÄÄ´ 7805 ÃÄÄÄÄÄÂÄÄÄ> +5.5V
RAW DC ³ ÀÄÄÄÂÄÄÄÙ ³
FROM ³ com³ ³
BRIDGE >2200uF ³+ _³_ ³
RECTIFIER 16V === \_/ 0.5v === 0.1u
& 8V AC ³ ³ ³
0V >ÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄ>
If the diode is an LED, the voltage increase could be 1 Ä 1.5V depending on the
colour & current fed through it.
Thermal stability poor, as it is dependent on Reg + diode, the diode drop will
alter quite a lot hot to cold.
in ÚÄÄÄÄÄÄÄ¿out
+24V >ÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ´ 7805 ÃÄÄÄÄÂÄÄÄ> +15.5V BOOST
³ ÀÄÄÄÂÄÄÄÙ ³ +15.0V NORMAL
RAW DC >2200uF³+ com_³_ ³
FROM 30V === /_\' ³
BRIDGE ³ NORMAL____³ 10V === 0.1u
RECTIFIER ³ BOOST O _³_ ³
& 17V AC ³ \o \_/ 0.5V ³
0V >ÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄ>
Thermal stability poor as it is dependent on Reg + Zener + diodes,
2/ Add a series R in the common leg. Most makes of regulator put about 50uA
constant current down the com----v------ X O/P ripple
13.8 ³ Unregulated
³ Dips
³
³
ÀÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄ>Time
90ø 180ø 270ø Supply Phase
B/ The maximium input voltage must not exceed the regulator max (eg 40V)
othewise it may well go short circuit & put 40V on the Output.
C/ Many regulator types have Thermal shutdown & the current rating of 100mA,
0.5A or 1A may be limited by poor heatsinking in practice. The higher the head
room voltage the more power has to be dissatisfied.
D/ The metal tabs must be insulated as they are connected to the regulator
common on positive types, which in not ground! They are also the most negative
part of a regulator so for -ve types that means the -ve input!
E/ If there is a possibility that the O/P may be powered but the input not a
diode must be put output to input across the regulator to protect it.
1N4001
ÚÄÄÄÄÄÄÄ´<ÃÄÄÄÄÄÄÄ¿
³ in ÚÄÄÄÄÄÄÄ¿out ³
>ÄÄÄÄÄÄÂÄÁÄÄÄÄ´ 7805 ÃÄÄÄÄÁÄÂÄÄÄÄ> eg a Floated
³ ÀÄÄÄÂÄÄÄÙ ³ Battery
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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