RD8 Просмотр технического описания (PDF) - Power Integrations, Inc
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RD8 Datasheet PDF : 12 Pages
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RD8
Component Listing
Reference
Value
Part Number
C1, C2
C3
C4
C5
C6
C7
D1-4
D5
L1
L2
R1
R2
R4
T1*
U1
U2
VR1
4.7 µF, 400 V
475CKH400M
68 pF, 1 kV
DD680
0.1 µF, 50 V
RPE121Z5U104M50V
2.2 nF, 250 VAC Y1
440LD22
330 µF, 16 V Low ESR ECA-1CFQ331L
100 µF, 25 V
ECE-A1EGE101
600 V, 1 A
1N4005
60 V, 1A, Schottky
11DQ06
5.5 mH (min), 0.1 A
Ferrite Bead, 3.5 X 11.4 mm 2743008112
2.2 Ω, 1 W
BW2F2.2Ω5%
4.7 kΩ, 1/4 W
5043CX4K700J
1.5 kΩ, 1/2 W, 5%
5053CX1K500J
TRD8
TNY254P
Optocoupler
LTV817
8.2 V 5% Zener
1N5237B
* For transformer sources, please visit the Power Integrations website at www.powerint.com.
Table 2. Parts List for the RD8.
Manufacturer
Illinois Capacitors
Philips
Murata
Cera-Mite
Panasonic
Panasonic
General Instrument
International Rectifier
Fair-Rite
RCD
Philips
Philips
Custom
Power Integrations
Liteon
Motorola
and the appropriate values of R4 and C3 required for snubbing
are easily determined. Traditional RCD or diode-Zener clamping
can also be used at a small additional cost for higher efficiency.
The secondary winding of T1 is rectified and filtered by D5, C6,
L2, and C7 to create the 9 V output voltage.
Zener diode VR1 and U2 sense the output voltage and provide
feedback to TinySwitch U1. The output voltage is set by the
combined voltage drops of Zener diode VR2 and the LED of
U2. Other output voltages are also possible by adjusting the
transformer turns ratio and the value of Zener diode VR1. A
resistor can be placed across the LED of U2 to provide
additional bias current (1-5 mA) to VR1. This improves
regulation and voltage accuracy. The extra bias current slightly
increases no load power consumption (15-75 mW).
Capacitors C1, C2, L1, R2, and Y1-capacitor C5 provide EMI
filtering for the power supply. At lower output power levels (or
for supplies designed to operate at 115 VAC only), L1 can be
replaced with a resistor, reducing system cost at the expense of
slightly lower efficiency.
Resistor R1 is a fusible resistor for protection against primary
fault conditions. This is a low cost alternative to a standard fuse,
accepted by safety agencies.
The RD8 power supply is designed to run in discontinuous
conduction mode, with the primary peak current set by the
TNY254P internal current limit. In this mode of operation, the
on-time for each switching cycle is set by the transformer
primary inductance, TinySwitch current limit and the high
voltage DC input bus. Output regulation is accomplished by
skipping switching cycles in response to an ON/OFF feedback
signal applied to the ENABLE pin. This differs significantly
from traditional PWM schemes that control the duty factor of
each switching cycle. Due to the ON/OFF nature of the
TinySwitch control scheme, the feedback optocoupler operates
in switching rather than in linear mode. Therefore the current
transfer ratio is not a critical factor as long as the optocoupler
provides enough current (50 µA) to activate the ENABLE pin
of the TinySwitch. This allows a low cost ungraded optocoupler
to be used.
For 115 V applications, 200 V rated capacitors can be used for
C1 and C2, and D5 can be replaced with a 40 V device (1N5819
or similar). If 200 V capacitors are used, then L1 can be
replaced with a resistor.
The circuit performance data shown in Figures 4-17 were
measured with AC voltage applied to the RD8.
Load Regulation (Figure 4) – The change in the DC output
voltage for a given change in output current is referred to as load
regulation. RD8 output voltage stays within ± 1% of nominal
from 0% to 100% of rated load current. The TinySwitch
regulation scheme enables this level of performance without the
use of a preload. The slight rise in output voltage at no load is
due to an increase in the voltage drop across VR1, caused by
3 C
3/99
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