RD7
®
TOPSwitch-II
PC Standby Reference Design Board
90 to 375 VDC Input, 3.5 W Output
Product Highlights
Low Cost Production Worthy Reference Design
• Up to 3.5 W of output power
• Meets Blue Angel requirements (5 W)
• Single sided board
• Low cost through-hole components
• Fully assembled and tested
• Easy to evaluate and modify
• Extensive performance data
• Light weight - no heat sink required for
TOPSwitch-II
• Non-isolated +12 V output option
Fully Protected by
TOPSwitch-II
• Primary safety current limit
• Output short circuit protection
• Thermal shutdown protects entire supply
Designed for World Wide Operation
• Designed for IEC/UL safety requirements
• Designed for wide range of input voltage
Typical Applications
• Desktop PC stand-by power supply (PS98, ATX, NLX,
SFX, Micro ATX)
• Consumer stand-by supply (e.g. TV, VCR, DVD)
Figure 1. RD7 Overall Physical Dimensions.
®
1.19 in.
(29 mm)
2 in. (48 mm)
.75 in.
(18 mm)
PI-2271-062998
PARAMETER
Input Voltage Range
Temperature Range
Output Voltage
(I
o
= 0.7 A)
Output Power
(continuous)
Line Regulation
(90-375VDC)
Load Regulation
(10%-100%)
Efficiency
(At full load)
Output Ripple Voltage
Safety
LIMITS
90 to 375 VDC
0 to 50° C
5 V
±
5%
3.5 W
±
1.0%
±
1.0%
72%
±
50 mV
IEC950/UL1950
Description
The RD7 reference design board is an example of a very low
cost production worthy DC input standby power supply design
using the
TOPSwitch-II
family of Three-terminal Off-line
PWM switchers. The reference design board is intended to help
TOPSwitch-II
users quickly develop their products. It provides
a basic design that can be easily modified to fit a particular
application. The RD7 operates from a rectified and filtered AC
mains voltage and provides 3.5 W output at 5 V. Features such
as a 12 V non-isolated output or tighter output voltage tolerance
may be implemented by changing only a few components (See
Figure 4).
Table 1. Table of Key Electrical Parameters.
April 1999
RD7
T1
C2
2.2 nF
1 KV
D2
C3
1N5822 270
µF
25 V
L1
3.3
µH
+
5 V – 5%
0.7 A
+
RF1
1
Ω
R1
47 kΩ
*
Css
VR1
IN5228C
C4
100
µF
25 V
-
C1
10 nF
1 KV
D1
UF4005
D3
1N4148
C6
0.1
µF
50 V
R3
100
Ω
U2
PC817A
Fusible
90-375 VDC
Input
-
D
TOPSwitch-II
CONTROL
C
R2
10
Ω
C
C
*
0.1
µF
C5
47
µF
10 V
S
TOP221P
U1
* optional component, not populated
PI-2187-062998
Figure 2. Schematic diagram of the RD7.
S/N
RF1
D2
R1
J1
C1
C2
D1
JP1
U1
C5
C6
D3
U2
R3
R2
C3
L1
VR1
T1
C4 J2
COMPONENT SIDE SHOWN
PI-2269-070298
Figure 3. RD7 Pinout and Component Legend.
CAUTION
The RD7 is designed for DC input. Please observe the proper polarity when applying power to this board.
Applying reverse polarity or AC power to the input terminals of the board can damage the
TOPSwitch.
2
B
4/99
RD7
Component Listing
Reference
C1
C2
C3
C4
C5
C6
C
c
*
C
ss
*
D1
D2
D3
L1
RF1
R1
R2
R3
T1**
U1
U2
VR1
Value
10 nF, 1 KV, Disc
2.2 nF 1 KV, Disc
270
µF
25 V
100
µF
25 V
47
µF,
10 V
0.1
µF,
50 V
0.1
µF,
50 V
600 V, 1A, UFR
40 V, 3 A, Schottky
75 V, Switching
3.3
µH,
5 A
1
Ω
Fuse Resistor 1/2 W
47 K, 1/2 W
10
Ω,
1/4 W
100
Ω,
1/4 W
Part Number
5GAS10
DD222
ECA-1EFQ271
ECE-A1EGE101
ECE-A1AGE470
ECU-S1H104MEA
ECU-S1H104MEA
UF4005
1N5822
1N4148
622LY-3R3M
BW1/2F 1
Ω
5%
5053CX47K00J
5043CX10R00J
5043CX100R0J
TRD7
TOP221P or TOP221G***
LTV817A
1N5228C
Manufacturer
Cera-Mite
Philips
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
General Instrument
General Instrument
Liteon
Toko
RCD
Philips
Philips
Philips
Custom
Power Integrations
Liteon
APD
Optocoupler, Controlled CTR
3.9 V, Zener, 2%
Table 2. Parts List For the RD7. (* Optional, for C
ss
values see Figure 9. **T1 is available from Premier Magnetics (714) 362-4211 as P/N
TDS-1185-9818, and from Coiltronics (561) 241-7876 as P/N CTX14-14193-X1. *** TOP221G can be used with layout modifications.)
General Circuit Description
The RD7 is a low-cost, flyback switching power supply using
the TOP221P. The circuit shown in Figure 2 provides a nominal
output power of 3.5 W at 5 VDC output. The power supply
operates from a DC voltage of 90 to 375 VDC. In a typical
application this DC voltage is derived from a rectified and
filtered AC main voltage of 85 to 265 VAC. The 5 V output is
directly sensed by optocoupler U2 and Zener diode VR1. The
output voltage is determined by the Zener diode (VR1) voltage
and the voltage drop across the optocoupler (U2) LED and
resistor R2. Other output voltages are possible by adjusting the
transformer turns ratios and the value of the Zener diode VR1.
The positive rail of the high voltage DC input is connected to
one side of the primary winding of T1. Capacitor C1 filters the
high voltage supply, and is necessary only if the connections
between the high voltage DC supply and the RD7 are long. The
other side of the transformer primary is driven by the integrated,
high-voltage MOSFET inside the TOP221. D1, R1, and C2
clamp voltage spikes caused by transformer leakage inductance
to a safe value and reduce ringing at the DRAIN of U1.
The secondary winding is rectified and filtered by D2 and C3
to generate a 5 V output. L1 and C4 provide additional filtering
to reduce high frequency ripple voltage. R3 and VR1 provide
a slight pre-load on the 5 V output to improve load regulation
at light loads. R3 also provides bias current for Zener VR1 to
improve regulation.
Soft start can be added to eliminate turn-on overshoot. With C
ss
placed across VR1, the optocoupler current is increased during
turn-on time. This increased current limits the duty cycle and
slows down the rising output voltage (See Figure 9). The bias
winding output is rectified and filtered by D3 and C6 to provide
a bias voltage for U2. C5 filters internal MOSFET gate drive
charge current spikes on the CONTROL pin, determines the
auto-restart frequency, and compensates the control loop. C
c
is
needed when the supply is operating in a noisy environment
(e. g. when the power supply is sharing the same input rectifier
and filter capacitor with another power supply). C
c
filters high
frequency noise.
The schematic of Figure 4 shows an enhanced version of the
RD7. The circuit comprising R2, R3, R4, R5 and U3 improves
overall output regulation to
±2%.
Optional soft start capacitor
C
ss
is used to eliminate turn-on overshoot. The bias supply
output can be used to provide a +12 V, non-isolated output by
changing C6 to 100
µF
as shown in Figure 4. C6 is added to
reduce output ripple to a primary load.
The circuit performance data shown in Figures 5 to 12 was
B
4/99
3
RD7
T1
C2
2.2 nF
1 KV
D2
1N5822
C3
270
µF
25 V
L1
3.3
µH
C4
100
µF
25 V
+
5 V – 2%
0.6 A
+
RF1
1
Ω
R1
47 kΩ
-
C1
10 nF
1 KV
D1
UF4005
C6
D3
100
µF
1N4148
35 V
R3
75
Ω
R4
10 kΩ
D
Fusible
90-375 VDC
Input
U2
PC817A
-
TOPSwitch-II
CONTROL
C
R2
150
Ω
S
TOP221P
U1
C
C
*
0.1
µF
C5
47
µF
10 V
*
C
SS
U3
TL431
R5
10 kΩ
+
12 V
Non-isolated
50 mA
-
* optional component, not populated
PI-2189-071098
Figure 4. Schematic diagram of the RD7 with 12V Non-isolated output.
measured with DC voltage applied to RD7.
Load Regulation (Figure 5(a) and 5(b)) - The amount of change
in the DC output voltage for a given change in output current is
referred to as load regulation. The 5 V output stay within
±1.0%
when the output current is between 0% to 100% of rated
load current at the 5 V output. The
TOPSwitch-II
over-
temperature protection circuit will safely shut down the power
supply under prolonged overload conditions. When the output
load is disconnected, R3 acts as a preload and the output stays
in regulation.
Line Regulation (Figure 6(a) and 6(b)) - The amount of change
in DC output voltage for a given change in the DC input voltage
is called line regulation. The maximum change in output
voltage is within
±1%.
Efficiency (Line Dependent). Efficiency is the ratio of output
power to the input power. The curve in Figure 7 shows how the
efficiency changes with input voltage using a 3.5 W load. The
efficiency is greater than 72% throughout the input range.
Efficiency (Load Dependent). The curves in Figure 8 show
how the efficiency changes with output power at 155 and 310
VDC inputs. The efficiency is greater than 70% for loads
greater than 2.5 W.
Power Supply Turn On Sequence. An internal switched, high
voltage current source provides the initial bias current for
TOPSwitch
when power is first applied. The waveforms shown
in Figure 8 illustrates the timing relationship between the high
voltage DC bus and 5 V output voltage for the RD7 circuit.
Capacitor C1 charges to the DC input voltage before
TOPSwitch
turns on. The delay of 130 ms (typical) is caused by the time
required to charge the auto-restart capacitor C5 to 5.7 V. At this
point the power supply turns on as shown.
Figure 10 shows the output voltage turn on transient as well as
a family of curves associated with the additional soft-start
capacitor C
ss
. The soft-start capacitor is placed across VR2 and
can range in value from 10
µF
to 47
µF
as shown.
Switching frequency ripple voltage is shown in Figure 11 for
the RD7 circuit at 155 VDC input and 3.5 W output. Peak to
peak ripple is less than 50 mV at 3.5 W.
The RD7 power supply transient response to a step load change
from 0.52 A to 0.75 A (75% to 100%) is shown in Figure 12.
The response is quick and well damped.
The RD7 is designed to meet worldwide safety specifications.
4
B
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RD7
Thermal Considerations
The RD7 utilizes the printed circuit copper for
TOPSwitch-II
heatsinking. With a copper area of approximately 0.227 in
2
(1.46 cm
2
) and 2 oz. (610 g/m
2
) copper cladding, the temperature
of the
TOPSwitch-II
rises 6
o
C at 50
o
C ambient temperature
and 3.5 W load.
winding. The use of triple insulated wire allows the transformer
to be constructed using a smaller core and bobbin than a conven-
tional magnet wire design due to the elimination of the creepage
margins required for safety spacing in a conventional design.
If a conventional margin wound transformer is desired, the
design of Figures 15 and 16 can be used. This design (TRD7-1)
uses an EEL16 core and bobbin to accommodate the 6 mm
creepage required to meet international safety standards when
using magnet wire rather than triple insulated wire, and has the
same pinout and printed circuit foot print as TRD7. The
transformer is approximately 50% taller than the triple insulated
wire design due to the inclusion of creepage margins required
to meet international safety standards.
Transformer Specifications
The electrical specifications and construction details for
transformer TRD7 are shown in Figures 13 and 14. Transformer
TRD7 is supplied with the RD7 reference design board. This
design utilizes an EE16 core and a triple insulated wire secondary
PI-2231-071098
Output Voltage (% of Nominal)
100
Output Voltage (% of Nominal)
VIN = 155 VDC
100
95
0
100
200
300
400
500
600
700
95
80
240
400
(a) 5 V Load Current (mA)
105
VIN = 310 VDC
100
(a) Input Voltage (VDC)
105
100
95
0
100
200
300
400
500
600
700
95
80
240
400
(b) 5 V Load Current (mA)
Figure 5 (a). Load Regulation at 155 VDC Input Voltage.
(b). Load Regulation at 310 VDC Input Voltage.
(b) Input Voltage (VDC)
Figure 6 (a). Line Regulation at 3.5 W Output.
(b). Line Regulation at 0.35 W Output.
Efficiency (%)
70
60
50
40
Po = 3.5 W
30
80
240
400
Input Voltage (VDC)
Figure 7. Efficiency vs. Input Voltage, 3.5 W Output.
PI-2235-062998
80
PI-2233-071098
105
105
B
4/99
5
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