Download 3-Terminal Positive Regulators

3-Terminal Positive Regulators
The LM140/LM340A/LM340/LM78XXC monolithic 3-terminal
positive voltage regulators employ internal current-limiting, thermal
shutdown and safe-area compensation, making them essentially
indestructible. If adequate heat sinking is provided, they can deliver
over 1.0A output current. They are intended as fixed voltage
regulators in a wide range of applications including local (on-card)
regulation for elimination of noise and distribution problems
associated with single-point regulation. In addition to use as fixed
voltage regulators, these devices can be used with external
components to obtain adjustable output voltages and currents.
Considerable effort was expended to make the entire series of
regulators easy to use and minimize the number of external
components. It is not necessary to bypass the output, although this
does improve transient response. Input bypassing is needed only if
the regulator is located far from the filter capacitor of the power
supply.
• There are common configurations for 78xx ICs,
including 7805 (5 volt), 7806 (6 volt), 7808
(8 volt), 7809 (9 volt), 7810 (10 volt), 7812
(12 volt), 7815 (15 volt), 7818 (18 volt), and
7824 (24 volt) versions. The 7805 is common,
as its regulated 5 volt supply provides a
convenient power source for most TTL
components.
• Complete specifications at 1A load
• Output voltage tolerances of ±2% at Tj = 25°C and
±4% over the temperature range (LM340A)
• Line regulation of 0.01% of VOUT/V of ΔVIN at 1A
load
• Internal thermal overload protection
• Internal short-circuit current limit
• Output transistor safe area protection
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Transformer: isolation and voltage conversion
Diode:rectification
Input capacitor(electrolytic): Filter
Input capacitor(AC): AC Filter
7815: regulator, a constant voltage
Resistance: capacitors to discharge
Output capacitor(electrolytic): to meet high
load current
• The maximum value of the output voltage of
the rectifier
Vdcgmax =
2.
VF
 VAK
a
• The amount of ripple voltage at the capacitor
is,
V = Içmax .Ty / Cg
• The minimum value of the output voltage of
the rectifier
Vdcgmin = Vdcgmax - V
• To avoid deterioration of the output voltage
Vdcgmin  Vdcç + 1 V
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VF : AC rms value
VAK : Voltage drop of diode
Vdcg : Input voltage at the regulator (DC)
Vdcç : Input voltage at the regulator (DC)
Iç
: DC output current
a
: Transformer turn ratio
V : The amount of ripple voltage at the
capacitor
• Ty : Half period of the AC main (10 ms)
• Cg : Input capacitor
To realize 12 V DC power supply, a single phase
transformer which is 220/2*12 is used to
insulation.
The voltage drop value of the diode is 0,6 V and
the input capacitor values is 470 F. The output
current is 100 mA ,
a) V
b) Min and max value of the DC voltage
a) V 
I ç maxTy
Cf
100.10 310.10 3

 2,12 V
6
470.10
b) Vdcg max  2Vdc  0.6  2.12  0.6  16,37
Vdcg min  Vdc  1
 Vdcg min  13 V
Vdcg min  Vdcg max  V  16,37  2,12  14,25 V