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參數(shù)資料
| 型號： | GM317 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | 3- TERMINAL ADJUSTABLE REGULATOR |
| 中文描述： | 3 -端可調(diào)穩(wěn)壓 |
| 文件頁數(shù)： | 6/8頁 |
| 文件大小： | 352K |
| 代理商： | GM317 |
GM317
6
APPLICATION INFORMATION
Basic Circuit Operation
The GM317 is a 3- terminal floating regulator. In opera-
tion, the GM317 develops and maintains a nominal
1.25V reference (Vref) between its output and adjust-
ment terminals. This reference voltage is converted to
a programming current flows through R2 to ground.
The regulated output voltage is given by:
Since the current from the adjustment terminal (I
)
ADJ
represents an error term in the equation, the GM317
was designed to control I
to less than 100μA and
ADJ
keep it constant. To do this, all quiescent operating cur-
rent is returned to the output terminal. This imposes
the requirement for a minimum load current. If the load
current is less than this minimum, the output voltage
will rise.
Since the GM317 is a floating regulator, it is only the
voltage differential across the circuit which is important
to performance, and operation at high voltages with re-
spect to ground is possible.
Vref= 1.25V Typical
Figure 8. Basic Circuit Configuration
Load Regulation
The GM317 is capable of providing extremely good
load regulation, but a few precautions are needed to ob-
tain maximum performance. For best performance, the
programming resistor (R1) should be connected as
close to the regulator as possible to minimize line
drops which effectively appear in series with the refer-
ence, thereby degrading regulation. The groung end of
R2 can be returned near the load ground to provide re-
mote ground sensing and improve load regulation.
External Capacitors
A 0.1μF disc or 1.0μF tantalum input bypass capaci-
tor (C ) is recommended to reduce the sensitivity to
IN
input line impedance.
The adjustment terminal may be bypassed to
ground to improve ripple rejection. This capacitor
(C
) prevents ripple from being amplified as the
ADJ
output voltage is increased. A 10μF capacitor should
improve ripple rejection about 15 dB at 120Hz in a
10V application.
Although the GM317 is stable with no output capaci-
tance, like any feedback circuit, certain values of ex-
ternal capacitance can cause excessive ringing. An
output capacitance (C ) in the form of a 1.0μF tanta-
O
lum or 25μF aluminum electrolytic capacitor on the
output swamps this effect and insures stability.
Protection Diodes
When external capacitors are used with any IC regu-
lator it is sometimes necessary to add protection di-
odes to prevent the capacitors from discharging
through low current points into the regulator.
Figure 9. shows the GM317 with the recommended
protection diodes for output for output voltage in ex-
cess of 25Vor high capacitance values (C > 25μF,
O
C
> 10μF). Diode D1 prevents C from discharg-
ADJ
O
ing thru the IC during an input short circuit. Diode D2
protects against capacitor C
discharging through
ADJ
the IC during an output short circuit.
The combination of diodes D1 and D2 prevents
C
from discharging through the IC during an in-
ADJ
put short circuit.
Figure 9. Voltage Regulator with Protection Diodes
GM317
V
IN
V
OUT
V
OUT
V
OUT
R1
R2
I
PROG
Adjust
I
ADJ
Vref
V
= Vref (1+ ) + I
R2
OUT
ADJ
R2
R1
V
IN
V
OUT
D1
R1
R2
Adjust
D2
1N4002
+C
O
1N4002
GM317
C
ADJ
C
IN
A
A
MICROELECTRONICS
GM317
Power Management
3- TERMINAL ADJUSTABLE REGULATOR
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