Datasheet RD7 Datasheet (POWER)

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

2 in. (48 mm)

®

1.19 in.

(29 mm)

Fully Protected by

• 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)

TOPSwitch-II

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).

.75 in.

(18 mm)

Figure 1. RD7 Overall Physical Dimensions.

PARAMETER

Input Voltage Range 90 to 375 VDC
Temperature Range 0 to 50° C
Output Voltage (I = 0.7 A)

Output Power (continuous) 3.5 W
Line Regulation (90-375VDC) ± 1.0%
Load Regulation (10%-100%) ± 1.0%
Efficiency (At full load) 72%
Output Ripple Voltage ± 50 mV
Safety IEC950/UL1950

Table 1. Table of Key Electrical Parameters.

o

LIMITS

5 V ± 5%

PI-2271-062998

April 1999

RD7

R1

C1

47 kΩ

D1

UF4005

+

90-375 VDC

Input

RF1

1

Ω

Fusible

10 nF

1 KV

-

D

TOPSwitch-II

CONTROL

S

TOP221P

U1

Figure 2. Schematic diagram of the RD7.

T1

C2

2.2 nF
1 KV

C

C

C

0.1 µF

*

D2

1N5822

D3

1N4148

C3

270 µF

25 V

0.1 µF
50 V

C5

47 µF

10 V

* optional component, not populated

C6

L1

3.3 µH

*

C

ss

VR1

IN5228C

C4

100 µF

25 V

+

5 V – 5%

0.7 A

-

R3

100 Ω

U2

PC817A

R2

10 Ω

PI-2187-062998

RF1

J1

U1

C5

Figure 3. RD7 Pinout and Component Legend.

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.

D2

U2

R1
C1

C6

S/N

C2

D1

JP1

D3

COMPONENT SIDE SHOWN

CAUTION

R2

R3

T1

VR1

C3

C4

L1

J2

PI-2269-070298

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Component Listing

Reference Value Part Number Manufacturer

C1 10 nF, 1 KV, Disc 5GAS10 Cera-Mite
C2 2.2 nF 1 KV, Disc DD222 Philips
C3 270 µF 25 V ECA-1EFQ271 Panasonic
C4 100 µF 25 V ECE-A1EGE101 Panasonic
C5 47 µF, 10 V ECE-A1AGE470 Panasonic
C6 0.1 µF, 50 V ECU-S1H104MEA Panasonic
Cc* 0.1 µF, 50 V ECU-S1H104MEA Panasonic
Css*
D1 600 V, 1A, UFR UF4005 General Instrument
D2 40 V, 3 A, Schottky 1N5822 General Instrument
D3 75 V, Switching 1N4148 Liteon
L1 3.3 µH, 5 A 622LY-3R3M Toko
RF1 1 Ω Fuse Resistor 1/2 W BW1/2F 1 Ω 5% RCD
R1 47 K, 1/2 W 5053CX47K00J Philips
R2 10 Ω, 1/4 W 5043CX10R00J Philips
R3 100 Ω, 1/4 W 5043CX100R0J Philips
T1** TRD7 Custom
U1 TOP221P or TOP221G*** Power Integrations
U2 Optocoupler, Controlled CTR LTV817A Liteon
VR1 3.9 V, Zener, 2% 1N5228C APD

RD7

Table 2. Parts List For the RD7. (* Optional, for Css values see Figure 9. **T1 is available from Premier Magnetics [phone] as P/N
TDS-1185-9818, and from Coiltronics [phone] 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
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. Cc 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). Cc 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
Css 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

ss

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3

RD7

RF1

1

+

Fusible

90-375 VDC

Input

-

T1

*

D2

1N5822

D3

1N4148

C6

100 µF

35 V

C5

47 µF

10 V

R1

47 kΩ

Ω

D1

UF4005

C1

10 nF

1 KV

D

TOPSwitch-II

CONTROL

S

TOP221P

U1

C2

2.2 nF
1 KV

C

C

C

0.1 µF

C3

270 µF

25 V

C

*

SS

U2

PC817A

L1

3.3 µH

R3

75 Ω

R2

150 Ω

U3

TL431

C4

100 µF

25 V

R4

10 kΩ

R5

10 kΩ

+

5 V – 2%

0.6 A

-

+

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 over­temperature 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 Css. 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.

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RD7

(b) Input Voltage (VDC)

Output Voltage (% of Nominal)

PI-2233-071098

80 240 400

100

100

95

95

105

105

(a) Input Voltage (VDC)

80 240 400

Thermal Considerations

The RD7 utilizes the printed circuit copper for TOPSwitch-II
heatsinking. With a copper area of approximately 0.227 in
(1.46 cm2 ) and 2 oz. (610 g/m2) copper cladding, the temperature
of the TOPSwitch-II rises 6 oC at 50 oC ambient temperature
and 3.5 W load.

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

105

100

95

105

0 100

200

300

(a) 5 V Load Current (mA)

VIN = 155 VDC

400

500

VIN = 310 VDC

600

PI-2231-071098

700

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 elimination of the creepage

2

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.

100

Output Voltage (% of Nominal)

95

0 100

200

(b) 5 V Load Current (mA)

Figure 5 (a). Load Regulation at 155 VDC Input Voltage.
(b). Load Regulation at 310 VDC Input Voltage.

300

600

400

500

80

70

60

50

700

Efficiency (%)

40

30

80 240 400

Po = 3.5 W

Input Voltage (VDC)

Figure 7. Efficiency vs. Input Voltage, 3.5 W Output.

Figure 6 (a). Line Regulation at 3.5 W Output.

(b). Line Regulation at 0.35 W Output.

PI-2235-062998

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B

5

RD7

PI-2245-071098

0

10 20

400

- 50

0

600

Output Voltage (mV)

Time (ms)

50

100

200

0

Output Current (mA)

80

150

100

50

0

4

2

60

40

20

Efficiency (%)

0

DC BUS VOLTAGE

OUTPUT

VOLTAGE

0.0

0.5 1.0 1.5

Output Power (W)

Figure 8. Efficiency vs. Output Power.

PI-2239-060498

VIN = 155 VDC
VIN = 310 VDC

2.0 2.5 3.0 3.5

6

5

4
3

2

Output Voltage (V)

1

0 µF

10 µF

PI-2237-060398

22 µF

PI-2241-060498

47 µF

0

0

Figure 9. Turn on Delay. Figure 10. Output Voltage Turn On Transient vs. Soft Start Capacitor.

200

150

100

50

0

-50

Output Voltage (mV)

-100

-150

-200
0

Figure 11. Switching Frequency Ripple, 155 VDC Input, 3.5 W Output.

100 200

Time (ms)

25 50

Time (µs)

0

0

10 20

Time (ms)

PI-2243-062998

Figure 12. Transient Load Response (75% to 100% of load).

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TRIPLE INSULATED SECONDARY TRANSFORMER (TRD1)

1

116 T

#37 AWG

2
3

14 T

#37 AWG

4

CORE# - PC40 EE16-Z (TDK)

GAP FOR AL OF 182 nH/T

9, 10

6 T

#26 AWG

Triple-insulated

6, 7

2

BOBBIN# - YW-193 (Yih Hwa Enterprises)

ELECTRICAL SPECIFICATIONS

PIN FUNCTION

1

HIGH-VOLTAGE DC BUS
2
3
4

6, 7

9, 10

TOPSwitch

PRIMARY-SIDE COMMON

V

BIAS

SECONDARY RETURN

OUTPUT

DRAIN

RD7

4

1

5

10

Electrical Strength

Creepage

Primary Inductance

Resonant Frequency

Primary Leakage Inductance

NOTE: All inductance measurements should be made at 100 kHz

Figure 13. Electrical Specification of Transformer TRD7.

60 Hz, 1 minute,

from pins 1-4 to pins 5-10

Between pins 1-4 and pins 5-10

All windings open
All windings open

Between pins 1-2 (pins 6-10 shorted)

3000 VAC

6.00 mm (min)
2430 µH –10%

500 kHz (min)

63 µH (max)

PI-2273-070298

4/99

B

7

RD7

TRIPLE INSULATED SECONDARY TRANSFORMER CONSTRUCTION

TAPE

TAPE

{

{

6, 7

9, 10

3
4

1
2

WINDING INSTRUCTIONS

Primary

Basic Insulation

Bias Winding

Basic Insulation

Secondary Winding

SECONDARY

BIAS

PRIMARY

Start at Pin 2. Wind one complete layer (about 58 turns)
of 37 AWG heavy nyleze wire from left to right. Insulate
first layer using 1 turn of polyester film tape, 8.3 mm
wide, 0.056 mm thick. Wind remaining 58 turns from
right to left for a total of 116 turns. Finish at Pin 1.

Apply 1 layer of tape for basic insulation.
Start at Pin 4. Wind 14 turns parallel bifilar of 37 AWG

wire from left to right in a single layer. Finish at Pin 3.
Apply 1 layer of tape for basic insulation.
Start at Pins 9, 10. Wind 6 turns parallel bifilar of 26 AWG

triple insulated wire from left to right. Finish on Pin 6, 7.

Outer Insulation

Final Assembly

* Triple insulated wire sources.

P/N: T27A01TXXX-3
Rubudue Wire Company
5150 E. La Palma Avenue
Suite 108
Anaheim Hills, CA 92807
[phone]
[phone] FAX

Figure 14. Construction Details of Transformer TRD7.

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P/N: order by description
Furukawa Electric America, Inc.
200 Westpark Drive
Suite 190
Peachtree City, GA 30269
[phone]
[phone] FAX

Apply 3 layers of tape for basic insulation.
Assemble and secure core halves.

Impregnate uniformly with varnish.

P/N: order by description
The Furukawa Electric Co., Ltd
6-1, Marunouchi 2-chome,
Chiyoda-ku, Tokyo 100, Japan
81-3-3286-3226
81-3-3286-3747 FAX

PI-2275-070298

RD7

MARGIN WOUND TRANSFORMER

1

116 T

#35 AWG

2
3

14 T

35 AWG

4

CORE# - PC40 EE16/24/5-Z (TDK)

GAP FOR AL OF 182 nH/T

9, 10

6 T

#26 AWG

6, 7

2

BOBBIN# - YW-035 (Yih Hwa Enterprises)

ELECTRICAL SPECIFICATIONS

Electrical Strength

Creepage

Primary Inductance

PIN FUNCTION

1

HIGH-VOLTAGE DC BUS

2

TOPSwitch DRAIN

3

PRIMARY-SIDE COMMON

4

V

BIAS

6, 7

9,10

RETURN
OUTPUT

60 Hz, 1 minute,

from pins 1-4 to pins 5-10

Between pins 1-4 and pins 5-10

All windings open

10

1

3000 VAC

6.0 mm (min)

2430 µH –10%

5

4

Resonant Frequency

Primary Leakage Inductance

Between pins 1-2 (pins 6-10 shorted)

NOTE: All inductance measurements should be made at 100 kHz

Figure 15. Electrical Specification of Transformer TRD7-1.

All windings open

300 kHz (min)

70 µH (max)

PI-2277-062998

4/99

B

9

RD7

MARGIN WOUND TRANSFORMER CONSTRUCTION

TAPE

TAPE

WINDING INSTRUCTIONS

{

{

SLEEVING

6, 7

9, 10

4
1

2

TAPE MARGINS

(4 PLACES)

SECONDARY

3

BIAS
PRIMARY

Safety Margin

Primary

Basic Insulation

Bias Winding

Reinforced Insulation

Safety Margin

Construct margins on each side of bobbin using 3 mm
wide tape. Match height of primary plus bias winding.

Start at Pin 2. Wind one complete layer (about 58 turns)
of 35 AWG heavy nyleze wire from left to right between
margins. Insulate first layer using 1 layer of polyester
tape (polyester film 11.5 mm (0.456 in) wide and 0.056
(2.2 mil) thick) for basic insulation. Wind remaining 58 turns
in second layer from right to left. Finish on Pin 1. Sleeve
start and finish leads using safety approved insulating
sleeving with 0.4 mm (0.016 in) minimum wall thickness.

Apply 1 layer of 11.5 mm wide tape for basic insulation.
Start at Pin 4. Wind 14 parallel bifilar turns of 35 AWG

heavy nyleze wire from left to right in a single layer.
Finish on Pin 3. Sleeve start and finish leads as above.

Apply 3 layers of tape (polyester film, 17.5 mm (0.689 in)
wide and 0.056 mm (2.2 mil) thick) for reinforced
insulation.

Construct margins on each side of bobbin using 3 mm
wide tape. Match height of secondary winding.

Secondary Winding

Outer Insulation

Final Assembly

Figure 16. Contruction Details of Transformer TRD7-1.

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Start at Pin 9 and 10. Wind 6 parallel bifilar turns of 26 AWG
heavy nyleze wire from left to right in a single layer. Finish
on Pin 6 and 7. Sleeve start and finish leads as above.

Apply 3 layers of 17.5 mm tape for outer insulation.
Assemble and secure core halves. Impregnate

uniformly with varnish.

PI-2281-062998

RD7

4/99

B

11

RD7

Revision

A
B

Notes

­Measurement method for primary leakage inductance of TRD7 and TRD7-1 corrected.

Date
9/98
4/99

Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability.
Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it
convey any license under its patent rights or the rights of others.

PI Logo and

TOPSwitch

are registered trademarks of Power Integrations, Inc.

©Copyright 1998, Power Integrations, Inc. 477 N. Mathilda Avenue, Sunnyvale, CA 94086 http://www.powerint.com

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Customer Service:
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Fax: +1•408•523•9365

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Fax: +1•770•424•6567

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