View AN-29_656877.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

february 2003 topswitch -gx flyback quick selection curves application note AN-29 quick start introduction this application note is intended for engineers starting a flyback power supply design with topswitch-gx . it offers a quick method to select the proper topswitch-gx device from parameters that are usually not available until much later in the design process. curves estimating the efficiency of the power supply and the corresponding topswitch-gx device dissipation are provided. they form a powerful tool for estimating cost and project requirements before even committing to or starting development. this application note is similar to both an-21 for topswitch-ii and an-26 for topswitch-fx . overview of quick selection curves the topswitch-gx quick selection curves (figures 1-4) show the expected power supply efficiency and topswitch-gx dissipation for typical flyback applications. power supplies with either a 5 v or a 12 v output, operating with either ?niversal input?(85 vac-265 vac) or ?ingle 230 vac input?(195 vac-265 vac) are described. the solid lines in the quick selection curves give a typical efficiency figure for a given load, depending upon the topswitch-gx device used. each solid line efficiency curve extends to the maximum power capability of the device, limited by device current limit. the superimposed dashed lines are contours of constant topswitch-gx device dissipation, the intersections of these dashed lines with the solid lines provide the corresponding dissipation at different loads. interpolation or extrapolation can find the dissipation at intermediate points. the shaded region indicates the output power where a flyback design at the given output voltage is no longer practical. this limit has been shown at an output current of 10 a and above. higher output currents are possible but such a design is typically not cost effective due to the size of the output diode and capacitors. higher output power can be obtained if the output voltage is higher. the curves can be used for both p (dip-8), g (smd-8) and y (to-220) packaged devices, however for the p and g parts the dissipation must be limited to 0.85 w. this is due to the thermal constraints of the p package. the p and g parts intentionally have lower current limits than their y packaged counterparts to match device dissipation to package capability. when using the curves for different output voltages the reader should be aware that altering the output voltage will give dramatic changes in efficiency. for voltages between 5 v and 12 v the data from both curves can be used to extrapolate an intermediate point. lower voltages will give lower efficiencies and limit maximum power capability. higher voltages will give higher efficiencies and greater power. for example from the curves a 12 v, 70 w universal design using the top249 has an estimated efficiency of 79.5%. if the output voltage were increased to 19 v this would increase to approximately 85%. similarly an open frame 1) determine which graph (fig. 1, 2, 3 or 4) is closest to your application. example: use figure 1 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-gx 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-gx curve. 6) read the topswitch-gx power dissipation from the dashed contours to determine heatsink requirements. 7) if the device dissipation is 0.85 w then the lower cost p/g packages can be considered. 8) start the design. use the topswich-gx transformer design spreadsheet or pi expert. note: see ?election curve assumptions? for limits of use.
AN-29 2 d 2/03 table 1. typical power supply component parameters for a topswitch-gx flyback power supply with a universal input (12 v output ). typical 12 v output power supply component parameters parameter units 242y 243y 244y 245y 246y 247y 248y 249y maximum transformer h 2780 1385 923 693 462 346 277 231 primary inductance lp transformer leakage %/lp 1.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 inductance secondary trace nh 30 30 30 30 30 30 30 30 inductance transformer resonant khz 750 800 850 900 950 1000 1050 1100 frequency (secondary open) transformer primary m ? 2400 1200 800 700 600 500 400 300 ac resistance transformer secondary m ? 30 15 10 8 6 4 2 1 ac resistance output capacitor m ? 24 18 15 12 10 8 6 4 equivalent series resistance @100 khz output inductor dc m ? 32 25 20 15 13 10 7.5 5 resistance common mode inductor m ? 370 340 310 280 250 220 190 160 dc resistance (both legs) core loss %/pin 22222222 universal input (85-265 vac) 230 vac, 250 w design is possible with the top249 at an output voltage of 48 v with an efficiency of 84.5%. note that curves for 19 v and 48 v are not provided. selection curve assumptions the selection curves are based on specific design assumptions that are detailed below: the switching frequency is 132 khz in all cases. for universal input the input bulk capacitor is sized at 3 f/w of the maximum load. for single voltage input the input bulk capacitor is sized at 1 f/w. ? v or (reflected voltage) of 135 v is assumed for all the curves. this is the output voltage reflected by the turns ratio to the primary side. ? zener primary clamp used to limit the leakage inductance spike is assumed to provide a constant clamping level of 200 v. practical implementation may require a parallel rc network to limit zener dissipation. all curves assume a schottky output diode. the 5 v output curves use a 45 v schottky diode with a forward drop of 0.4 v. the 12 v output curves use a schottky diode with a forward voltage drop of 0.54 v. besides the design criteria above, typical power supply component parameters used in generating the data for the quick selection curves are provided in tables 1 to 4. for 5 v designs using the top246 or larger the secondary trace inductance must be reduced as the output power increases to limit clamp dissipation. this is reflected in the table data. the efficiency curves are valid only when using the component values shown in tables 1 to 4. changes to these parameters may give different results. selecting the correct topswitch-gx this section explains how to select the correct topswitch-gx using the curves (figures 1-4). the procedure uses the curves to estimate efficiency of the power supply and the corresponding dissipation in the topswitch-gx device . start with the output power of the application on the x-axis. move vertically to the intersection with the first topswitch-gx curve (solid line) and then read the efficiency directly from the y-axis. from the same intersection point on the topswitch-gx
AN-29 3 d 2/03 curve, interpolate the topswitch-gx power dissipation from the constant power dissipation contours (dashed lines). some output power levels can be delivered by more than one topswitch-gx device. when moving vertically from the x-axis, the first curve encountered will be the smallest, lowest cost topswitch-gx device, while the last curve encountered will be the largest, most efficient topswitch-gx device suitable for the desired output power. thermal requirements and packaging of the proposed power supply may call out for a more efficient device rather than the smallest or lowest-cost possibility. in addition the p and g packages (8 pin dip) have a practical dissipation limit of around 0.85 w in a 50 c ambient, giving a device junction temperature of ~100 c. this ensures that there is adequate margin to thermal shutdown including device variation. typical temperatures above 110 c are not recommended. the to-220 package does not have this limit due to the ability to mount the tab to a suitably sized heatsink. example 1: 30 w universal application consider a 5 v / 30 w power supply with universal input range. from the curves in figure 2, we can see that the top244 can deliver 30 w (x-axis) with an estimated efficiency (y-axis) of about 67.5%. the projected topswitch-gx dissipation is approximately 3.5 w. alternatively continuing the top245 could be used with an efficiency of 70.5% and a device disspation of approximately 2.5 w. as the dissipation is above 0.85 w, y packaged devices should be used. the thermal environment and the available heatsinking must still be evaluated to confirm the choice of device in this application. example 2: 12 w adapter application consider a 12 w, 12 v supply with universal input range. from the curves in figure 1 we see that a top243 or top244 could be used, top243 with an efficiency of 82% and a device dissipation of 0.7 w or a top244 with an efficiency of 83% and a device dissipation of 0.5 w. the top242 is ruled out as we require to use the p package and therefore are limited to a dissipation of less than 0.85 w this is an adapter design in an enclosed plastic box, so the maximum power available from the supply is limited by thermal considerations. the worst-case external ambient (t a_ext ) is typical 5 v output power supply component parameters parameter units 242y 243y 244y 245y 246y 247y 248y 249y maximum transformer h 2780 1385 923 693 462 346 277 231 primary inductance lp transformer leakage %/lp 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 inductance secondary trace nh 20 20 20 20 19 16 13 10 inductance transformer resonant khz 750 800 850 900 950 1000 1050 1100 frequency (secondary open) transformer primary m ? 2000 1060 700 600 500 300 200 100 ac resistance transformer secondary m ? 12 64321 0.75 0.5 ac resistance output capacitor m ? 18 9654321 equivalent series resistance @100 khz output inductor dc m ? 6 4.5 3.5 3 2.5 2 1.5 1 resistance common mode inductor m ? 370 340 310 280 250 220 190 160 dc resistance (both legs) core loss %/pin 22222222 universal input (85-265 vac) table 2. typical power supply component parameters for a topswitch-gx flyback power supply with a universal input (5 v output) .
AN-29 4 d 2/03 50 c with an estimated temperature rise of 20 c inside the plastic box, giving an internal ambient (t a_int ) of 70 c. as a topswitch-gx in a p-package is desired, from the datasheet we obtain the thermal impedance from junction-to- ambient ( ja ) of 60 c/w (645 mm 2 / 1.0 sq. inch of 2 oz. copper clad for heatsinking). we first perform the following calculation for the most cost- effective device. if found unsuitable, we must repeat the calculation for the more expensive device. tt p ja int ja d =+ ? () for the top243p, we see that thermally the top243p design is not acceptable. recalculating using the top244p. with a smaller dissipation the top244p is just acceptable. a junction temperature of 100 c provides sufficient margin for device-to-device r ds(on) variation. example 3: 70 w universal application consider a 70 w, 12 v power supply with universal input range. from the curves in figure 2 we see that there are four possible device choices: a) top246y: the projected efficiency is 73.8% and the device dissipation is 8 w. b) top247y: the projected efficiency is 77% and the device dissipation is 5.5 w. c) top248y. the projected efficiency is 78.5% and the device dissipation is 4.5 w. d) top249y: this is the least cost effective device but has the highest projected efficiency of 79.5% and the lowest device dissipation of 3.9 w. the thermal environment and the available heatsinking must now be evaluated to confirm the final choice of device in this application from the short list above. again increasing the output voltage would increase the efficiency and decrease dissipation (e.g. 70 w, 19 v, 85-265 vac gives 85% efficiency). typical 12 v output power supply component parameters parameter units 242y 243y 244y 245y 246y 247y 248y 249y maximum transformer h 3190 1593 1062 797 531 398 319 265 primary inductance lp transformer leakage %/lp 1.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 inductance secondary trace nh 30 30 30 30 30 30 30 30 inductance transformer resonant khz 750 800 850 900 950 1000 1050 1100 frequency (secondary open) transformer primary m ? 5600 2800 1840 1200 1000 800 600 400 ac resistance transformer secondary m ? 30 15 10 8 6 4 2 1 ac resistance output capacitor m ? 24 18 15 12 10 8 6 4 equivalent series resistance @100 khz output inductor dc m ? 32 25 20 15 13 10 7.5 5 resistance common mode inductor m ? 370 340 310 280 250 220 190 160 dc resistance (both legs) core loss %/pin 22222222 single voltage input (230 vac 15%) table 3. typical power supply component parameters for a topswitch-gx flyback power. tc j =+ = 70 60 0 5 100 (.) tc j =+ = 70 60 0 7 112 (.)
AN-29 5 d 2/03 other key considerations we have seen how to use the information provided by the topswitch-gx quick selection curves. however there are other key factors to consider when completing the power supply design. these can produce results that differ from the predictions of the quick selection curves. factors which can lower the performance: input capacitor tolerance and aging should be taken into account. lower capacitance decreases the dc input voltage, increasing primary rms currents and hence giving larger conduction losses in the device chosen. in production, the primary inductance of the transformer will also have a significant tolerance. inductances higher than those in tables 1 to 4 will cause the power supply to operate beyond recommended design guidelines (k rp too low). values of primary inductance significantly lower than those in tables 1 to 4 would lead to higher peak and rms drain current in the topswitch-gx mosfet. this causes an increase in device dissipation and also causes the device to reach current limit at less than maximum load. the quick selection curves assume that the ac input voltage waveform is a pure sine wave. if the input voltage waveform is distorted, the resultant peak voltage on the input bulk capacitor may be much lower than anticipated. this causes the topswitch-gx device to reach current limit or duty cycle limit at less than the maximum possible load. therefore, in locations where significant line distortion is expected, the designer should provide a suitable design margin. this can be accomplished by derating maximum output power or increasing the input capacitance. some wattmeters give erroneous readings when the current has a high crest factor. it is important to use an instrument designed for the purpose. the voltech pm100 is an example. ? inimum line frequency is important. a low line frequency requires larger carryover periods for the input bulk capacitor, causing high voltage ripple across it. if the line frequency expected to be lower than 50 hz, the input capacitor should be sized appropriately or the maximum output power be derated. typical 5 v output power supply component parameters parameter units 242y 243y 244y 245y 246y 247y 248y 249y maximum transformer h 3190 1593 1062 797 531 398 319 265 primary inductance lp transformer leakage %/lp 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 inductance secondary trace nh 20 20 20 20 19 16 13 10 inductance transformer resonant khz 750 800 850 900 950 1000 1050 1100 frequency (secondary open) transformer primary m ? 4600 2400 1600 1200 1000 800 600 400 ac resistance transformer secondary m ? 12 64321 0.75 0.5 ac resistance output capacitor m ? 18 9654321 equivalent series resistance @100 khz output inductor dc m ? 6 4.5 3.5 3 2.5 2 1.5 1 resistance common mode inductor m ? 370 340 310 280 250 220 190 160 dc resistance (both legs) core loss %/pin 22222222 single voltage input (230 vac 15%) table 4. typical power supply component parameters for a topswitch-gx flyback power supply with a single input (5 v output).
AN-29 6 d 2/03 the choice of v or can affect the efficiency greatly. for example increasing the v or (turns ratio) may allow a schottky diode on the output, for higher efficiency, by reducing the diode inverse voltage. however it will increase secondary reflected leakage and therefore clamp dissipation. lowering the v or reduces secondary reflected leakage, reducing clamp dissipation but at the expense of higher primary rms currents, increasing the topswitch-gx conduction losses. for low voltage outputs, the secondary currents and their associated losses can become significant. close attention must be paid to the ?sr?(equivalent series resistance) of the output capacitor in particular. the values in tables 2 and 4 for the 5 v quick selection curves (figures 2 and 4) use capacitors with very low-esr. energy stored in the leakage inductance is dumped into primary clamp (rcd clamp or zener clamp) when the topswitch-gx turns off. therefore the efficiency will fall significantly if the leakage inductance is too high. refer to example 3 of an-26 to see how the effective in-circuit leakage should be measured and how secondary trace inductance reflects into the primary. for low voltage outputs at high power, it is critical to minimize leakage inductance. factors which can improve performance: for more experienced designers, there are ways to improve the performance indicated by the quick selection curves. some of these are now mentioned briefly: the recommended capacitance per watt is based on the optimum cost to performance ratio. better performance can certainly be obtained in terms of efficiency, topswitch-gx dissipation and life expectancy of the input bulk capacitor, by using a higher capacitance per watt than recommended. if the intended application is for 100/115 vac only, the clamp voltage and v or may be raised by a calculated amount provided no voltage doubler is being used at the input of the power supply. this will enhance the overall efficiency and lower the device dissipation. the recommended primary inductances in tables 1 to 4 are based on the minimum permissible k rp at the maximum power capability of the device. in other words, the primary inductance along any given solid curve corresponding to a particular device has been kept a constant. however in an adapter application for example, the output power is limited by thermal considerations to a value much less than the maximum power capability of the topswitch-gx device. this presents an opportunity to improve efficiency and lower device dissipation by increasing the primary inductance while ensuring that the k rp at the actual power requirement stays within recommended design limits. since the quick selection curves are based on a topswitch-gx junction temperature of 100 c at low line, full load, better performance is possible if the topswitch-gx runs cooler. good heatsinking will help in achieving higher efficiency. increasing the v or can be helpful in some cases. a high v or decreases the reverse voltage stress on the output diodes. this may allow the use of 45 v schottky output diodes for high voltage outputs, resulting in a significant improvement in the efficiency. this step should be taken only after considering the overall impact. it should be mentioned that increasing the v or causes an increase in the duty cycle and a corresponding reduction in the rms currents and conduction losses in the topswitch-gx device provided the overall efficiency is not adversely affected due to increased clamp loss. conclusions the topswitch-gx devices may be considered to be an extension of the topswitch-fx family. the p-package options have reduced current limits to match the device current limit to the thermal dissipation capability of the package. this allows for a smaller transformer in adapter designs. however for the same conditions both the p/g and y packaged devices will dissipate the same power. therefore the quick selection curves are valid for either package (up to the point where current limiting takes place).
AN-29 7 d 2/03 figure 1. efficiency vs. output power with contours of constant topswitch-gx power loss for universal input and 12 v output. figure 2. efficiency vs. output power with contours of constant topswitch-gx power loss for universal input and 5 v output. 6810 20 30 50 100 200 4 pi-2676-100900 efficiency (%) universal input (85 vac to 265 vac) 5 v output 60 70 69 67 68 66 65 64 63 62 61 78 77 76 75 74 73 72 71 79 2 w 10 w 11 w 13 w 80 output power (w) top242 1 w 1.5 w 2 w 3 w 4 w 5 w 6 w 7 w 12 w 9 w top245 top243 top244 top249 top248 top247 top246 1.5 w 8 w 10 a output current* *see "overview of quick selection curves" 0.5 w 41020305 0 100 200 pi-2678-100900 efficiency (%) universal input (85 vac to 265 vac) 12 v output 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 output power (w) 8 w 10 w 18w top242 top243 top244 top245 top246 top247 top248 top249 0.5w 1 w 1.5 w 7 w 2 w 3 w 4 w 5 w 6 w 11 w 9 w 12 w 14 w 16 w 10 a output current* *see "overview of quick selection curves"
AN-29 8 d 2/03 figure 3. efficiency vs. output power with contours of constant topswitch-gx power loss for single voltage application and 12 v output. figure 4. efficiency vs. output power with contours of constant topswitch-gx power loss for single voltage application and 5 v output. 610 20 100 120 200 300 single voltage input (230 vac 15%) 12 v output 75 76 77 78 79 80 81 82 83 84 85 0.5 w 1 w 3 w 86 output power (w) pi-2677-100900 efficiency (%) 1.5 w 2 w 7 w 5 w 9 w 11 w 8 w top242 top243 top244 top245 top246 top247 top248 top249 4 w 6 w 10 w 12 w 14 w *see "overview of quick selection curves" 10 a output current* 610 20 50 100 200 300 efficiency (%) 80 79 78 77 76 0.5 w 1 w 1.5 w 2 w 2 w 4w 6 w 7 w 13 w 75 74 73 72 71 70 69 68 67 66 65 output power (w) pi-2675-100900 single voltage input (230 vac 15%) 5 v output 3w 9 w 10 w 11 w 12 w 14 w 5 w top243 top245 top247 top244 10 a output current* *see "overview of quick selection curves" top242 top246 top248 top249 8 w
AN-29 9 d 2/03 notes
AN-29 10 d 2/03 notes
AN-29 11 d 2/03 notes
AN-29 12 d 2/03 notes - 1) updated package references. 2) corrected spelling. 3) updated nomenclature. 4) corrected heading on table 4. 5) corrected topswitch-gx reference in figures. 1) corrected device dissipation for p/g packages. date 11/00 7/01 2/03 revision b c d singapore power integrations, singapore 51 goldhill plaza #16-05 republic of singapore 308900 phone: +65-6358-2160 fax: +65-6358-2015 e-mail: singaporesales@powerint.com 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 for the latest updates, visit our web site: www.powerint.com patent information 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 p atent rights or the rights of others. the products and applications illustrated herein (including circuits external to the products and transformer construction) may be covered by one or more u.s. and foreign patents or potentially by pending u.s. and foreign patent applications assigned to power integrations. a complete l ist of power integrations?patents may be found at www.powerint.com. life support policy power integrations' products are not authorized for use as critical components in life support devices or systems without the express written approval of the president of power integrations, inc. as used herein: 1. life support devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, a nd whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a signi ficant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expecte d to cause the failure of the life support device or system, or to affect its safety or effectiveness. the pi logo, topswitch , tinyswitch , linkswitch and ecosmart are registered trademarks of power integrations, inc. pi expert and dpa-switch are trademarks of power integrations, inc. ?opyright 2003, power integrations, inc. taiwan power integrations international holdings, inc. 17f-3, no. 510 chung hsiao e. rdl, sec. 5, taipei, taiwan 110, r.o.c. phone: +886-2-2727-1221 fax: +886-2-2727-1223 e-mail: taiwansales@powerint.com china power integrations international holdings, inc. rm# 1705, bao hua bldg. 1016 hua qiang bei lu shenzhen guangdong, 518031 china phone: +86-755-8367-5143 fax: +86-755-8377-9610 e-mail: chinasales@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 korea power integrations international holdings, inc. 8th floor, dongsung building, 17-8 yoido-dong, youngdeungpo-gu, seoul, 150-874, korea phone: +82-2-782-2840 fax: +82-2-782-4427 e-mail: koreasales@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 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 applications hotline applications fax world wide +1-408-414-9660 world wide +1-408-414-9760

▲Up To Search▲

Price & Availability of AN-29

	To Download AN-29 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .