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PDF LR8 Data sheet ( Hoja de datos )
| Número de pieza | LR8 | |
| Descripción | High Input Voltage Adjustable 3-Terminal Linear Regulator | |
| Fabricantes | Supertex Inc | |
| Logotipo |  |
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LR8
LR8
High Input Voltage
Adjustable 3-Terminal Linear Regulator
Features
❏ 12V to 450V input voltage range
❏ Adjustable 1.20V to 440V output regulation
❏ 5% output voltage tolerance
❏ Output current limiting
❏ 10µA typical ADJ current
❏ Internal junction temperature limiting
Applications
❏ Off-line SMPS startup circuits
❏ Adjustable high voltage constant current source
❏ Industrial Controls
❏ Motor controls
❏ Battery chargers
❏ Power supplies
General Description
The Supertex LR8 is a high voltage, low output current, adjustable
linear regulator. It has a wide operating input voltage range of
12V to 450V. The output voltage can be adjusted from 1.20V to
440V provided that the input voltage is at least 10V greater than
the output voltage. The output voltage can be adjusted by means
of two external resistors R1 and R2 as shown in the typical
application circuits. The LR8 regulates the voltage difference
between VOUT and ADJ pins to a nominal value of 1.20V. The
1.20V is amplified by the external resistor ratio R1 and R2. An
internal constant bias current of typically 10µA is connected to
the ADJ pin. This increases VOUT by a constant voltage of 10µA
times R2.
The LR8 has current limiting and temperature limiting. The
output current limit is typically 15mA and the minimum temperature
limit is 125°C. An output short circuit current will therefore be
limited to 15mA. When the junction temperature reaches its
temperature limit, the output current and/or output voltage will
decrease to keep the junction temperature from exceeding its
temperature limit. For SMPS start-up circuit applications, the
LR8 turns off when an external voltage greater than the output
voltage of the LR8 is applied to VOUT of the LR8. To maintain
stability, a bypass capacitor of 1.0µF or larger and a minimum DC
output current of 500µA are required.
The device is available in TO-92, TO-243AA (SOT-89), and
TO-252 (D-PAK) packages.
LR8 Block Diagram and Typical Application
VIN
C1
*
VV
IN OUT
ADJ
LR8
VOUT
R1
C2
R2
RLOAD
*Required for conditions where VIN is less than VOUT.
12/03/01
Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability
indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to
workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the
Supertex website: http://www.supertex.com. For complete liability information on all Supertex prod1ucts, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.
1 page  
Typical Performance Curves
V V =1.2V
IN OUT
LR8
ADJ
12V
2.4KΩ
1.0µF
12V,
200V,
400V
V V =1.2V
IN OUT
LR8
ADJ
I
ADJ
2.4KΩ
1.0µF
V
IN
V =5.0V
OUT
IOUT
LR8
ADJ
6.04KΩ
±1%
25V
1.0µF
RLOAD
18.2KΩ
±1%
Temperature Variation
1.30
1.25
1.20
1.15
1.10
1.05
1.00
-50
-25
0 25 50 75
T(junction) (°C)
100 125
Adjustment Current
12
11
10
VIN = 400V
9 VIN = 12V
8
VIN = 200V
7
6
-50 -25
0 25 50 75
T(junction) (°C)
100 125
Load Regulation
5.2
5.1
5.0
4.9
4.8
0
5
246
IOUT (mA)
8 10
LR8
5 Page 
The minimum capacitance required for given boot-up time is
given by the following equation:
COUT
> tBOOT
IPWM − ILIM
VHYS
where
COUT = Capacitor at LR8 output
tBOOT = Time required for supply to bootstrap
IPWM = Current used by PWM controller
ILIM = LR8 current limit (10mA min)
VHYS = PWM controller UVL hysteresis
Remember that this equation is valid only when PWM current
exceeds the LR8’s current limit.
LR8
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100 • FAX: (408) 222-4895
11 www.supertex.com
11/30/01rev.1
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet LR8.PDF ] | |
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