POWER RD8 Datasheet

RD8

PI-2252-091098

0.80 in.

(20 mm)

1.30 in.

(33 mm)

1.80 in. (45 mm)

TinySwitch

Reference Design Board

85 to 265 VAC Input, 3 W Output

Low Cost Production Worthy AC

Adapter Reference Design

• Cost competitive with linear solutions (regulated 50/ 60 Hz transformers)

• Lowest component count switching solution

• Ultra low no-load power consumption (30/70 mW @115/ 230 VAC)

• Simple low cost two-winding transformer

• Greater than 72% efficiency

• Low average EMI, only one inductive component required for EMI filtering

• Small size

Designed for World Wide Operation

• Designed for IEC/UL safety requirements

• Meets FCC/VDE Class B EMI specifications

• Wide range input voltage

Figure 1. RD8 Board Overall Physical Dimensions.

PARAMETER LIMITS

Description

The RD8 reference design board is an example of a low cost production worthy design for an AC wall adapter or similar applications requiring small size, high efficiency, and low cost. The RD8 utilizes the TNY254 member of the TinySwitch family of low cost Off-line Switchers from Power Integrations. It is intended to help TinySwitch users develop their products quickly by providing a production ready design which needs little or no modification to meet system requirements. The RD8 is designed to replace conventional linear AC wall adapters, offering universal input range, smaller size, and high efficiency, all at a competitive cost. The RD8 is cost-competitive with linear solutions (regulated 50/60 Hz transformers).

The unique ON/OFF control scheme of Tinyswitch virtually eliminates energy consumption at no load. Typical linear wall adapters consume 1-4 watts at no load, which costs $1-$4 per year ( based on $0.12/kWhr). In comparison, a typical TinySwitch supply consumes 30-70 mW at no load, offering substantial energy savings.

Input Voltage Range 85 to 265 VAC Input Frequency Range 47 to 440 Hz Temperature Range 0 to 50°C Output Voltage (I = 0.33 A) 9 V ± 7%* Output Power (continuous) 3 W Line Regulation (85-265 VAC) ± 0.5% Load Regulation (0%-100%) ± 1% Efficiency (PO = 3 W) 72% (min)

Standby Power Consumption (115/230 VAC)

Output Ripple Voltage ± 75 mV Safety IEC 950 / UL1950

EMI

* Can be improved to ± 5% by using a more accurate Zener (± 2%). Table 1. Table of Key Electrical Parameters.

30/70 mW (typical)

VFG243B (Quasi-Peak)

VFG46 B (Average)

CISPR22 B

FCC Part 15 "B"

March 1999

RD8

5 mH

85-265

VAC

1N4005

2.2 Ω

Fusible

1N4005

4.7 µF 400 V

1N4005

4.7 kΩ

4.7 µF 400 V

1.5 kΩ 1/2 W

68 pF

Figure 2. Schematic Diagram of the 3 W RD8 Power Supply.

TNY254P

TinySwitch

EN BP

11DQ06

0.1 µF

LTV817

330 µF

16 V

2.2 nF

Y1 Safety

Bead

VR1

1N5237B

100 µF

25 V

+ 9 V

RTN

PI-2250-090398

COMPONENT SIDE SHOWN*

Figure 3. Component Legend for the RD8.

General Circuit Description

The RD8 is a low-cost flyback switching power supply using the TNY254P integrated circuit. The circuit shown in Figure 2 details a 9 V, 3 W power supply that operates from 85 to 265 VAC input voltage, suitable for replacing conventional linear supplies in cost-sensitive applications such as AC wall adapters.

AC power is rectified and filtered by D1-4, C1, and C2 to create

VR1

Jmp 1

* Shown 1.5 X actual size

the high voltage DC bus applied to the primary winding of T1. R4 and C3 clamp the primary leakage spike and also reduce EMI. At this power level, a simple RC network is sufficient for snubbing leakage spikes. Because of the relatively low switching frequency of TinySwitch (44 kHz), and its ON/OFF control method, the additional capacitive loading of the RC snubber network has a much smaller effect on efficiency than for conventional PWM switchers running at higher switching frequencies. Since TinySwitch runs in current limit mode at all times regardless of output load, the worst case leakage spike

PI-2254-091597

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Component Listing

Reference Value Part Number Manufacturer

C1, C2 4.7 µF, 400 V 475CKH400M Illinois Capacitors C3 68 pF, 1 kV DD680 Philips C4 0.1 µF, 50 V RPE121Z5U104M50V Murata C5 2.2 nF, 250 VAC Y1 440LD22 Cera-Mite C6 330 µF, 16 V Low ESR ECA-1CFQ331L Panasonic C7 100 µF, 25 V ECE-A1EGE101 Panasonic D1-4 600 V, 1 A 1N4005 General Instrument D5 60 V, 1A, Schottky 11DQ06 International Rectifier L1 5.5 mH (min), 0.1 A L2 Ferrite Bead, 3.5 X 11.4 mm 2743008112 Fair-Rite R1 2.2 Ω, 1 W BW2F2.2Ω5% RCD R2 4.7 kΩ, 1/4 W 5043CX4K700J Philips R4 1.5 kΩ, 1/2 W, 5% 5053CX1K500J Philips T1* TRD8 Custom U1 TNY254P Power Integrations U2 Optocoupler LTV817 Liteon VR1 8.2 V 5% Zener 1N5237B Motorola

* For transformer sources, please visit the Power Integrations website at www.powerint.com.

RD8

Table 2. Parts List for the RD8.

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.

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.

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

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

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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.

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

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.

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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

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