View AN-21_446253.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

TOPSwitch-II Flyback Quick Selection Curves
Application Note AN-21
Introduction
This application note is for engineers starting a flyback power supply design with TOPSwitch-II. It offers a quick method to select the proper TOPSwitch-II device from parameters that are usually not available until much later in the design process. The TOPSwitch-II Flyback Quick Selection Curves provide the essential design guidance. Efficiency and TOPSwitch-II power dissipation are two important performance parameters to the flyback power supply designer. Both can be easily measured or accurately estimated after the power supply is designed. But what if the designer must make project and resource decisions before actually committing to and starting development? This application note helps the designer quickly select the optimum TOPSwitch-II device from simple curves of estimated efficiency and TOPSwitch-II power dissipation.
(R)
(R)
QUICK START
1) Determine which graph (Fig. 2, 3, 4 or 5) is closest to your application. Example: Use Figure 2 for Universal input, 12 V output. 2) Find your power requirement on the X- axis. 3) Move vertically from your power requirement until you intersect with a TOPSwitch-II curve (solid line). 4) Read the associated efficiency on the Y- axis. 5) Determine if this is the appropriate efficiency for your application. If not, continue to the next TOPSwitch-II curve. 6) Read TOPSwitch-II power dissipation from the dashed contours to determine heatsink requirements. 7) Start the design. Use the Transformer Design Spreadsheet from AN-17.
Note: See Selection Curve Assumptions for limits of use.
Typical Power Supply Losses
Power supplies have an input power which, because of internal dissipation, can be significantly higher than the output power. Efficiency, defined as the ratio of output power to input power, indicates how much power is dissipated in the power supply. In the typical TOPSwitch-II flyback power supply shown in Figure 1, most of the power dissipation occurs in output rectifier D2, Zener diode VR1 (or equivalent clamp circuit) and the TOPSwitch-II device. Other components, such as output filter inductor L1, input common mode inductor L2, and bridge rectifier BR1, contribute lesser power dissipation terms. Overview of Quick Selection Curves The TOPSwitch-II Flyback Quick Selection Curves consider these dissipation terms (and others as well) to provide a good estimate of expected efficiency for both Universal input and 230 VAC mains applications. Figure 2 (for +12 V outputs) and Figure 3 (for +5 V outputs) show a set of curves for efficiency and TOPSwitch-II power dissipation versus output power for the entire family of TOP221-TOP227 devices. These curves assume operation from a low line AC input voltage of 85 VAC, which is a suitable value for all Universal input applications.
For higher nominal mains voltages, including 208, 220, 230, and 240 VAC, a low line AC input voltage of 195 VAC is used to generate similar curves found in Figure 4 (for +12 V outputs) and Figure 5 (for +5 V outputs). For all curves, the maximum AC mains voltage is assumed to be 265 VAC. For each TOPSwitch-II device, a family of efficiency curves (solid lines) is plotted on the Y-axis as a function of output power on the X-axis. TOPSwitch-II power dissipation is plotted separately on the same graph as a family of constant power dissipation contours (dashed lines).
April 1998
AN-21
D2 MUR610CT L1 3.3 H 15 V C2 1000 F 35 V 6, 7 D1 BYV26C L2 33 mH BR1 400 V 2 4 D3 1N4148 U2 NEC2501 C3 120 F 25 V RTN
1
9, 10
C1 47 F 400 V
VR1 P6KE200
R2 200 1/2 W
C4 0.1 F 5 T1 C6 0.1 F F1 3.15 A C7 1.0 nF Y1 R1 510 C9 0.1 F U3 TL431 R3 6.2 R5 10 k
R4 49.9 k
D
TOPSwitch-II
CONTROL
C
L N J1
S
U1 TOP224Y
C5 47 F
PI-2158-031698
Figure 1. Typical Flyback Power Supply Using TOP224.
Selecting the Right TOPSwitch-II
Using Figures 2, 3, 4 and 5 First we use the Power versus Efficiency curves to find the efficiency of the power supply for each TOPSwitch-II device that will deliver the output power. Then we estimate the TOPSwitch-II loss from the contours of constant power dissipation. Start with the output power of the application on the X-axis. Move vertically to the intersection with the first TOPSwitch-II curve and then read the efficiency directly from the Y-axis. From the same intersection point on the TOPSwitch-II curve, interpolate the TOPSwitch-II power dissipation from the constant power dissipation contours. Some output powers can be delivered by more than one TOPSwitch-II device. When moving vertically from the Xaxis, the first curve encountered will be for the smallest, lowest cost TOPSwitch-II device, while the last curve will be for the largest, most efficient TOPSwitch-II device suitable for the desired output power.
Example 1: 30 W Universal Application Assume a +5 V application requires 30 W of output power from Universal input voltage. From the curves in Figure 3, the TOP224 can deliver 30 W with an estimated Y-axis efficiency of 71%. The projected TOPSwitch-II power dissipation is approximately 2.5W. The TOP225 can also be used with an expected efficiency of 75% and interpolated power dissipation of approximately 1.7 W. With these curves, a heat sink can be selected or evaluated immediately because an estimate for TOPSwitch-II power dissipation is now available before the design is even started! Example 2: 30 W Application from 230 VAC Consider a +12 V output at 30 W from 230 VAC input. Figure 4 shows the TOP223 is the optimum device with an expected efficiency slightly over 85% and power dissipation of approximately 0.75 W. Example 3: TOPSwitch-II Temperature It is easy to estimate the junction temperature TJ of the TOPSwitch-II from the ambient temperature TA and the
2
B 5/98
AN-21
effective junction to ambient thermal impedance JA. This technique works for any TOPSwitch-II package as long as the overall thermal impedance is known, which includes the selected TOPSwitch-II thermal impedance, the thermal interface to a heatsink, and the effective thermal impedance of the heatsink itself. For example, with a TOP225 dissipation PD of 1.7 W, ambient temperature TA of 40 C, and overall thermal impedance JA of 20 C/W, the maximum TOPSwitch-II junction temperature TJ can be found as follows:
Adjusting for Minimum Input Voltage
Using Figures 6 and 7 To use the power ratio curves, start on the X-axis with the desired minimum AC input voltage. Move vertically to the intersection with the curve. Read the value of the power ratio from the Y-axis. The effective output power at the originally assumed minimum mains voltage of 85 or 195 VAC is simply the actual required output power divided by this ratio. The effective output power at 85 or 195 VAC mains voltage is used as the X-axis value for the curves given in Figures 2-5. The effective output power at 85 or 195 VAC will generate the same TOPSwitch-II loss (obtained from the curves in Figures 2-5) as the actual required output power at the modified AC input voltage. This ratio also scales the primary inductance to a value appropriate for the different input voltage. The original curves are derived from the typical values in Table 3, which is discussed later in this application note. In addition, TOPSwitch-II duty cycle limitations require a linear reduction in reflected voltage VOR for AC mains voltages below 85 VAC, as shown in Figure 7. Example 4: Input Voltage Adjustment Suppose an application for only the US market requires 35 W of output power at +12 V. The lowest AC input voltage is typically 90% of 115 VAC or 103.5 VAC. Find the power ratio from Figure 7 to be 1.15. The effective output power, obtained by dividing the actual output power by the power ratio, is
TJ = TA + ( PD x JA ) = 40 C + (1.7 W x 20 C/W ) = 74 C
The design should limit TJ to less than 100 C at the maximum ambient temperature.
Available Power
The minimum AC input voltage has a strong influence on the choice of TOPSwitch-II device for a given output power. If the minimum voltage is increased above the values assumed for the curves in Figures 2 through 5, then more power will be available from each TOPSwitch-II device. We can use the Output Power Ratio Curves in Figures 6 and 7 together with the original curves of Figures 2 through 5 to determine the available power for different input voltages. Figure 6 gives a ratio curve for 230 VAC mains at low line while Figure 7 shows a similar curve for low line Universal mains applications.
Effective Output Power =
PARAMETER Switching Frequency (fs) Transformer Reflected Voltage (VOR) Clamp Voltage (VCLAMP) Output Schottky Rectifier Forward Voltage (VD) Primary Bias Voltage (VB) VALUE 100 kHz 135 V 200 V 0.4 V 16 V Optocoupler Transistor Current Optocoupler LED Current
35 W = 30.4 W 1.15
195 VAC 5.0 mA
85 VAC 3.5 mA
3.5 mA
5.0 mA
Table 2. Typical Power Supply Parameters that Change with TOPSwitch-II Duty Cycle.
Table 1. Power Supply Parameters Independent of Input Voltage and Output Power.
B 5/98
3
AN-21
TYPICAL POWER SUPPLY COMPONENT PARAMETERS
PARAMETER Transformer Primary Inductance Transformer Leakage Inductance (referred to the primary) Transformer Resonant Frequency (measured with secondary open) Transformer Primary Winding Resistance Transformer Secondary Resistance Output Capacitor Equivalent Series Resistance Output Inductor DC Resistance Common Mode Inductor DC Resistance UNITS H H kHz TOP221 TOP222 TOP223 TOP224 TOP225 TOP226 TOP227 8650 175 4400 90 2200 45 1475 30 1100 22 880 18 740 15
400
450
500
550
600
650
700
m
5000
1800
650
350
250
175
140
m
20
12
7
5
4
3.5
3
m
30
24
18
15
13
11.5
10
m
40
32
25
20
16
13
10
m
400
370
333
300
267
233
200
Table 3. Typical Power Supply Component Parameters for TOPSwitch-II Flyback Power Supply.
This effective output power is then used with the curves in Figure 2 to select the TOPSwitch-II device and to estimate the TOPSwitch-II dissipation. Predictions of efficiency and power dissipation may be less accurate when the ratio is used. The new value of primary inductance is the product of the power ratio and original inductance value in Table 3. The new inductance value for the TOP224 would be:
Typical values are given in Table 2 for two parameters that depend only on input voltage. These parameters change with TOPSwitch-II duty cycle. The remaining power supply parameters depend on the output power. Table 3 gives typical values for the power-dependent parameters
LP = 1475 H x 1.15 = 1696 H
Input Capacitance
Efficiency and output power are both strong functions of bulk energy storage capacitor C1. For the Universal AC Mains curves, the numerical value of C1 in microfarads is assumed to be at least three times the maximum output power in watts. For 230 VAC mains, the C1 value (F) is assumed to be at least equal to the maximum output power (watts). For example, for 30 W of output power, the bulk energy storage capacitor C1 is expected to be at least 90 F for Universal mains and 30 F for 230 VAC mains applications. The design must consider the tolerance of the capacitor to guarantee expected performance from the power supply.
Selection Curve Assumptions
Several physical power supply parameters must be calculated, estimated, or measured to determine efficiency. Measured values can differ significantly from the curves' predictions if the design parameters are not the same as the typical values used to generate the curves. Typical values are given in Table 1 for several parameters that are independent of power level and input voltage. These parameters are defined and discussed in AN-16 and AN-17.
4
B 5/98
AN-21
Lower values of input capacitance will reduce the available output power. Going from 3 to 2 F per watt will decrease the output power by as much as 15% for Universal input. The available power falls dramatically for values less than 2 F per watt. The value of capacitor C1 also determines the average value of the DC bus voltage. The Universal VAC Mains curves in Figures 2 and 3 were generated with an average DC bus value of 105 VDC while the 230 VAC Mains curves in Figures 4 and 5 were generated with an average DC bus value of 265VDC. * Use a DC voltage source to prevent AC ripple voltage from modulating the duty cycle. Efficiency depends heavily on actual DC input voltage. A convincing experiment is to vary the DC voltage 15 V to see how efficiency varies over the range of expected AC ripple voltage. * Measure transformer leakage inductance accurately. Take into account inductance of external circuitry, which can increase effective leakage inductance by 30% or more. * Measure switching frequency accurately for the individual TOPSwitch-II in the circuit to account for component-tocomponent variations. * Verify actual clamp voltage. Effective clamp voltage can be 230 VDC or higher, even though the clamp Zener diode is specified to be 200 V. See AN-16 for details. Determine which physical power supply parameters do not match the typical values in Table 3. Change (temporarily) to components that match the parameters in the table until measured efficiency matches the predicted value.
Other Considerations
Curves in this application note were generated from the typical power supply parameters in Tables 1, 2 and 3. If measured efficiency in a particular TOPSwitch-II application does not agree with the values predicted from the curves, it is likely the physical parameters of the measured power supply do not match the tabular values. Use the guidelines below to get best agreement between measurements and predictions. * When measuring efficiency from an AC source, use an electronic wattmeter designed for average input power measurements with high-crest factor current waveforms. Do not simply measure RMS input voltage and RMS input current. The product of these two measurements is input volt-amperes or input burden (VA), not the real input power in watts.
B 5/98
5
AN-21
UNIVERSAL INPUT (85 VAC TO 265 VAC) 12 V OUTPUT
84 0.25 W
PI-2160-031898
82
Efficiency (%) at 85 VAC
80
0.5 W
78 76 74
0.75 W
3W 1.0 W 2W 2.5 W 1.5 W
TOP222 TOP221 TOP223
4W 5W 6W
TOP224 TOP225 TOP226
72 70 68 4 6
12
14 W
TOP227 80 100 40 60
8
10
15
20
30
Output Power (W) at 85 VAC
Figure 2. Typical Efficiency vs Output Power with Contours of Constant TOPSwitch-II Power Loss for Universal Input and 12 V Output.
UNIVERSAL INPUT (85 VAC TO 265 VAC) 5 V OUTPUT
PI-2162-040298
80 78 0.25 W 76 74 72 70 68 66 TOP221 64 62 TOP224 60 58 4 6 8 10 15 20 30 40 60 80 100 TOP222 0.5 W 0.75 W
Efficiency (%) at 85 VAC
1.0 W 2.0 W 1.5 W 2.5 W 4W 6W 5W
TOP223
3W
TOP227
12
W
14 W
8W
10 W
TOP225 TOP226
Output Power (W) at 85 VAC
Figure 3. Typical Efficiency vs Output Power with Contours of Constant TOPSwitch-II Power Loss for Universal Input and 5 V Output.
6
B 5/98
W
8W
10 W
AN-21
SINGLE VOLTAGE INPUT (230 VAC 15%) 12 V OUTPUT
PI-2164-040298
87
86
Efficiency (%) at 195 VAC
85 0.25 W 84 0.5 W 83 0.75 W
1.0 W 1.5 W
2.0 W
4W
3W 2.5 W
82 TOP221 81 TOP222 TOP223 TOP224
TOP225 TOP226 TOP227
80 7 8 9 10 15 20 30 40 60 80 100 150 200
Output Power (W) at 195 VAC
Figure 4. Typical Efficiency vs Output Power with Contours of Constant TOPSwitch-II Power Loss for Single Voltage Application and 12 V Output.
SINGLE VOLTAGE INPUT (230 VAC 15%) 5 V OUTPUT
PI-2166-040298
80 0.25 W 78 0.5 W
Efficiency (%) at 195 VAC
76 0.75 W TOP221 74
1.0 W
1.5 W
TOP222
2.0 W 2.5 W 3W
4 W
72
TOP223 TOP224
70 TOP225 68
5
W
5W
6W
TOP227
6W
TOP226
7
8
9 10
15
20
30
40
60
80
100
150
200
Output Power (W) at 195 VAC
Figure 5. Typical Efficiency vs Output Power with Contours of Constant TOPSwitch-II Power Loss for Single Voltage Application and 5 V Output.
B 5/98
7
AN-21
POWER RATIO: SINGLE VOLTAGE (230 VAC 15%)
Output Power Ratio (195 VAC)
PI-2168-040498
POWER RATIO: UNIVERSAL INPUT (85 TO 265 VAC)
Output Power Ratio (85 VAC)
PI-2170-040498
1.15 1.1 1.05 1 0.95 0.9 0.85 140 160 180 200 220 POUT VOR
1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 60 70 80 90 100 POUT VOR
240
Low Line AC Input Voltage (VAC)
110
Low Line AC Input Voltage (VAC)
Figure 6. Power Ratio vs Low Line AC Input Voltage of Nominal 230 VAC.
Figure 7. Power Ratio and VOR vs Low Line AC Input Voltage for Universal Input.
For the latest updates, visit our Web site: www.powerint.com 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. The PI Logo, TOPSwitch, TinySwitch and EcoSmart are registered trademarks of Power Integrations, Inc. (c)Copyright 2001, Power Integrations, Inc.
WORLD HEADQUARTERS AMERICAS Power Integrations, Inc. 5245 Hellyer Avenue San Jose, CA 95138 USA Main: +1 408-414-9200 Customer Service: Phone: +1 408-414-9665 Fax: +1 408-414-9765 e-mail: usasales@powerint.com KOREA Power Integrations International Holdings, Inc. Rm# 402, Handuk Building 649-4 Yeoksam-Dong, Kangnam-Gu, Seoul, Korea Phone: +82-2-568-7520 Fax: +82-2-568-7474 e-mail: koreasales@powerint.com EUROPE & AFRICA Power Integrations (Europe) Ltd. Centennial Court Easthampstead Road Bracknell Berkshire, RG12 1YQ United Kingdom Phone: +44-1344-462-300 Fax: +44-1344-311-732 e-mail: eurosales@powerint.com JAPAN Power Integrations, K.K. Keihin-Tatemono 1st Bldg. 12-20 Shin-Yokohama 2-Chome Kohoku-ku, Yokohama-shi Kanagawa 222-0033, Japan Phone: +81-45-471-1021 Fax: +81-45-471-3717 e-mail: japansales@powerint.com TAIWAN Power Integrations International Holdings, Inc. 17F-3, No. 510 Chung Hsiao E. Rd., Sec. 5, Taipei, Taiwan 110, R.O.C. Phone: +886-2-2727-1221 Fax: +886-2-2727-1223 e-mail: taiwansales@powerint.com INDIA (Technical Support) Innovatech #1, 8th Main Road Vasanthnagar Bangalore, India 560052 Phone: +91-80-226-6023 Fax: +91-80-228-9727 e-mail: indiasales@powerint.com CHINA Power Integrations International Holdings, Inc. Rm# 1705, Bao Hua Bldg. 1016 Hua Qiang Bei Lu Shenzhen, Guangdong 518031 China Phone: +86-755-367-5143 Fax: +86-755-377-9610 e-mail: chinasales@powerint.com APPLICATIONS HOTLINE World Wide +1-408-414-9660 APPLICATIONS FAX World Wide +1-408-414-9760
8
B 5/98

▲Up To Search▲

Price & Availability of AN-21

	To Download AN-21 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .