RD8 データシートの表示（PDF） - Power Integrations, Inc
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RD8 Datasheet PDF : 12 Pages
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RD8
General Circuit Description (cont.)
higher average Zener current. This effect can be corrected by
adding a Zener bias resistor across the LED side of U2. This
resistor also provides a small preload, further improving no load
regulation.
Line Regulation (Figure 5) - The change in the DC output
voltage for a given change in the AC input voltage is called line
regulation. The maximum change in output voltage versus line
for the RD8 is within ± 0.5%.
Efficiency (Line Dependent) – Efficiency is the ratio of the
output power to the input power. The curves in Figures 6 and 7
show the efficiency as a function of input voltage. Note that the
efficiency is relatively constant over the entire input voltage
range.
Efficiency (Load Dependent) – The curves in Figures 8 and 9
show how the efficiency changes with output power for 115 VAC
and 230 VAC inputs. Due to the TinySwitch regulation scheme,
the efficiency is relatively constant from 0-100% of output load.
Power Supply Turn On Sequence –The waveforms shown in
Figure 10 illustrate the relationship between the high-voltage
DC bus and the 9 V output voltage. Since the TinySwitch
internal power consumption is extremely small and is derived
entirely from the DRAIN, the supply starts switching almost as
soon as power is applied, as shown in Figure 10. The output
achieves regulation approximately 8 ms after power is applied,
with no overshoot.
Power Supply Turn Off Sequence - Figure 11 shows the decay
of the 9 V output when the AC input is removed. The 9 V
decays monotonically to zero after AC power is removed, with
no spurious pulses.
Output Ripple - Line frequency ripple voltage is shown in
Figure 12 for 115 VAC input and 3 W output. Switching
frequency ripple voltage is shown in Figure 13 for the same test
condition. In Figure 13, note the skipped pulses due to the
TinySwitch ON/OFF control.
Load Transient Response - The output transient response to a
step load change from 0.26 to 0.33 A (75% to 100%) is shown
in Figure 14. Note that the load transient is extremely small
(< 20 mV), and recovers within 100 µs. The small step in the
load response is due to the finite load regulation of the RD8.
No Load Power Consumption - Figure 15 shows no load power
consumption as a function of input voltage. The no load power
consumption for the RD8 is only 10 to 20% of the standby
power consumption of a typical linear power supply.
The RD8 is designed to meet worldwide safety and EMI (FCC
B and VDE B) specifications. Measured conducted emissions
are shown in Figure 16 for 115 VAC and Figure 17 for
230 VAC. In the RFI measurements performed on the RD8,
peak measurements were applied to the quasi-peak limits
specified by the test agencies. A peak measurement is more
stringent than a quasi-peak or average measurement, since there
is no averaging of the EMI signal form the supply under test.
Peak measurements are also simpler and easier to perform using
a standard spectrum analyzer.
Figure 16 shows the results of a peak EMI scan at 115 VAC and
full output load, compared to the FCC B quasi-peak limit. The
RD8 passes the FCC B quasi-peak limits with margin using a
peak EMI measurement. Applying quasi-peak measurement to
the RD8 will result in EMI levels 3-4 dB lower than shown in
Figure 16. This is true because the RD8 skips pulses to achieve
regulation, resulting in substantially lower quasi-peak and
average EMI levels than for a peak measurement.
Most European EMI standards specify test limits for both
quasi-peak and average measurement. The supply under test
must pass both the average and quasi-peak limits to achieve
certification. Figure 17 shows peak and average EMI scans
performed at 230 VAC input and full load, compared to the
VFG243 B quasi-peak limit and the VFG46 B average limit.
The VFG243 and VFG46 specifications incorporate the same
test limits as CISPR22, but also include frequencies below
150 kHz. The RD8 peak measurement passes the VFG 243 B
quasi-peak limit with substantial margin, and almost passes the
VFG46 B average limit. The average measurement passes the
VFG46 B average limit with a minimum of 6 dB margin.
In both the 115 V and 230 V measurements, there is almost no
EMI at frequencies of 4 MHz and above. This is due in part to
the relatively low operating frequency of TinySwitch (44 kHz
nominal). The lack of high frequency emissions allows easy
compliance with international radiated emissions limits.
Transformer Specification
The electrical specifications and construction details for
transformer TRD8 are shown in Figures 18 and 19. Transformer
TRD8 is supplied with the RD8 reference design board. Since
no auxiliary bias winding is required to power TinySwitch, the
transformer design is very simple, requiring only a primary and
secondary winding.
The TRD8 design utilizes an EE16 core and a triple insulated
wire secondary winding. The use of triple insulated wire allows
the transformer to be constructed using a smaller core and
bobbin than a conventional magnet wire design due to the
4C
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