POWER RD7 Datasheet

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.

LIMITS

5 V ± 5%

PI-2271-062998

April 1999

RD7

47 kΩ

UF4005

90-375 VDC

Input

RF1

Ω

Fusible

10 nF

1 KV

TOPSwitch-II

CONTROL

TOP221P

Figure 2. Schematic diagram of the RD7.

2.2 nF 1 KV

0.1 µF

1N5822

1N4148

270 µF

25 V

0.1 µF 50 V

47 µF

10 V

* optional component, not populated

3.3 µH

VR1

IN5228C

100 µF

25 V

5 V – 5%

0.7 A

100 Ω

PC817A

10 Ω

PI-2187-062998

RF1

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.

R1 C1

S/N

JP1

COMPONENT SIDE SHOWN

CAUTION

VR1

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 (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 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

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RD7

RF1

Fusible

90-375 VDC

Input

1N5822

1N4148

100 µF

35 V

47 µF

10 V

47 kΩ

Ω

UF4005

10 nF

1 KV

TOPSwitch-II

CONTROL

TOP221P

2.2 nF 1 KV

0.1 µF

270 µF

25 V

PC817A

3.3 µH

75 Ω

150 Ω

TL431

100 µF

25 V

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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