By G8MNY (Updated Feb 05)
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There are 3 ways 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
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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 common leg, so a small R can uplift the voltage.

in ÚÄÄÄÄÄÄÄ¿out
+22V >ÄÄÄÂÄÄÄÄÄÄ´ 7812 ÃÄÄÂÄÄÄÄÄ> +13.80V
RAW DC ³ ÀÄÄÄÂÄÄÄÙ ³
FROM >2200uF ³+ com³ ³
BRIDGE 30V === Multi 10K === 0.1u
RECTIFIER ³ Turn ³ ³
& 16V AC 0V >ÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄ>

Thermal stability is good, as it is dependent on Reg + the constant current through the R, but that will be regulator make dependent.

3/ Add a voltage offset ratio arm. The 330 & 1k pot give a zero to 4x max ratio arm, that magnifies the regulator voltage by up to 4 times, plus any voltage gained by adding resistance in series with the common leg.

in ÚÄÄÄÄÄÄÄ¿out
+24V>ÄÄÄÄÄÂÄÄÄÄ´ 7805 ÃÄÄÂÄÄÄÄÂÄÄÄ> +5V to +20V
RAW DC ³ ÀÄÄÄÂÄÄÄÙ ³ ³
FROM >2200uF ³+ com ³ 330R ³
BRIDGE 30V === ³ ³ === 0.1u
RECTIFIER ³ ³ 1V ³
& 17V AC ³ ÀÄÄÄÄ>POT ³
³ ³ ³
0V >ÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄ>

Thermal stability good, as it is dependent on Reg/multiplier ratio.


NOTES
A/ For all 3 types the input must always exceed the O/P by at least 2V so that the regulator's drop out voltage is always exceeded. There are low drop out types available (0.3V - 1V).

Volts
Off load 25_³ _ _ _ _ _ _ _ _ _ _ _ _
On load __³ __ Discharge __ v
Peak 23 ³ /' `-._ /' Capacitor
Mean 19 --³ / `-._ / Peak-Peak Headroom is
Min 16 __³/Charge `-._/ Ripple the voltage
³ Drop-out V ^ above Dropout
Reg O/P -³-----------------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 (e.g. 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 dissipated.

D/ The metal tabs must be insulated as they are connected to the regulator common on positive types, which is 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> e.g. a Floated
³ ÀÄÄÄÂÄÄÄÙ ³ Battery



Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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