1 description lt 8302 micropower no-opto isolated flyback converter demonstration circuit 2014a is a micropower no-opto isolated flyback converter featuring the lt ? 8302. this demo circuit outputs 5v, and maintains tight regulation with a load current from 10ma to 2.2a over an input voltage from 10v to 30v. the output current capability increases with the input voltage. the LT8302 typically needs less than 0.5% of its full output power as a minimum load to maintain good output voltage regulation. on the dc2014a, in order to avoid pre-loading, a 5.6v zener diode is placed between its v out + and v out C to serve as a minimum load. transformer leakage inductance causes a voltage spike on the primary side after the power switch turns off. to limit this leakage inductance spike within mosfet volt - age rating of 65v, an rc snubber and a tvs clamp are installed to damp the ringing and clamp the mosfet drain voltage to a safe level. the performance summary table summarizes the perfor - mance of the demo board at room temperature. the demo circuit can be easily modified for different applications with some pre-designed transformers. l , lt, ltc, ltm, burst mode, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. performance summary the lt ? 8302 is a simple to use monolithic micropower isolated flyback converter. by sampling the isolated output voltage directly from the primary -side flyback waveform, the part requires no third winding or opto-isolator for regulation. the output voltage is programmed with two external resistors and a third optional temperature compen - sation resistor. by integrating the loop compensation and soft-start inside, the part reduces the number of external components. boundary mode operation provides a small magnetic solution with excellent load regulation. low ripple burst mode ? operation maintains high efficiency at light load while minimizing the output voltage ripple. a 3.6a, 65v dmos power switch is integrated along with all the high voltage circuitry and control logic into a thermally enhanced 8-lead so package. the LT8302 data sheet gives a complete description of the part, operation and application information. the data sheet must be read in conjunction with this quick start guide for demo circuit 2014a. design files for this circuit board are available at http://www .linear.com/demo specifications are at t a = 25c parameter conditions min typ max units input voltage 10 24 30 v output voltage v in = 10v to 30v, i out = 10ma to 2.2a 4.75 5 5.25 v maximum output current v in > 15v 2.2 a output voltage ripple (peak to peak) v in = 10v to 30v, i out = 2.2a 100 mv typical switching frequency v in = 24v, i out = 2.2a 345 khz minimum switching frequency i out = 0ma 12 khz efficiency v in = 10v, i out = 2.2a v in = 24v, i out = 2.2a v in = 30v, i out = 2.2a 80 84 84 % % % dc2014af demo manual dc2014a
2 quick start procedure demonstration circuit 2014a is easy to set up to evaluate the performance of the LT8302. refer to figure 1 for proper measurement equipment setup and follow the procedure: 1. with power off, connect the input power supply to the board through v in (e1) and gnd (e2) terminals. con - nect the load to the terminals v out + (e3) and v out C (e4) on the board. 2. turn on the power at the input. increase v in slowly to 10v . note: make sure that the input voltage is always within spec. to operate the board with higher input/output volt - age, input capacitor, output capacitor and output diode with higher voltage ratings are needed. 3. check for the proper output voltages. the output should be regulated at 5.0v (5%). note: the LT8302 requires very small minimum load to maintain good output voltage regulation. a zener diode is placed on the output to clamp the voltage to 5.6v. this zener can be replaced with a 560 resistor at the tradeoff of lower efficiency. 4. once the proper output voltage is established, adjust the input voltage and load current within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. note : when measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. measure the input or output voltage ripple by touching the probe tip directly across the v in (e1) and gnd (e2), or v out + (e3) and v out C (e4) terminals. see figure 2 for proper scope probe technique. + ? + ? + ? + ? power supply i in i out v out v in + ? load + ? input or output capacitor figure 1. proper measurement equipment setup figure 2. proper scope probe placement for measuring input or output ripple dc2014af demo manual dc2014a
3 quick start procedure figure 3. typical efficiency and regulation curves 5v out efficiency vs load current 5v out load and line regulation figure 4. v out ripple and switch node voltage waveforms at different load conditions figure 5. load transient responses (v in = 24v, load transient between 1a and 2a) load current (ma) 0 65 efficiency (%) 90 85 80 75 70 95 1200 1600 2000 400 dc2014 f03 800 v in = 30v v in = 24v v in = 10v load current (ma) 0 4.80 output voltage (v) 5.05 5.00 4.95 4.90 4.85 5.10 1200 1600 2000 400 dc2014 f04 800 v in = 30v v in = 24v v in = 10v 1s/div v out 50mv/div v sw 20v/div dc2014a f04a 1s/div v out 50mv/div v sw 20v/div dc2014a f04b 20s/div v out 20mv/div v sw 20v/div dc2014a f04c 1ms/div v out 100mv/div i out 1a/div dc2014a f05 v in = 24v, i out = 0, low ripple burst mode v in = 24v, i out = 0.5a, discontinuous mode v in = 24v, i out = 2.2a, quasi-resonant boundary mode dc2014af demo manual dc2014a
4 parts list item qty reference part description manufacturer / part number required circuit components 1 1 c1 cap.,alum. elec. 22f, 50v, nippon chemi-com, emza500ada220mf61g 2 1 c2 cap., chip, x5r, 10f, 50v, 10% 1210 taiyo yuden, umk325bj106k 3 1 c3 cap., chip, x5r, 1f, 25v, 10% 0603 avx , 06033d105 kat 2a 4 1 c4 cap., chip, c0g, 220pf, 50v, 5% 0805 avx , 08055a221 jat 2a 5 3 c5, c6, c7 cap., chip, x5r, 100f, 6.3v, 10% 1210 avx , 12106d107 kat 2a 6 1 c8 cap., chip, x7r, 4.7nf, 250v, 10% 1812 muratr , ga343drgd472kw01l 7 1 d1 diode, pds1040l, powerdi-5 diodes inc., pds1040l-13 8 1 d2 diode, cmhz5232b, sod-123 central semi., cmhz5232b 9 1 d3 diode, smaj18a, sma diodes inc., smaj18a-13-f 10 1 d4 diode, cmmsh1-100, sod-123f central semi., cmmsh1-100g tr 11 1 r1 res., chip, 1m, 1/10w, 1% 0603 vishay , crcw06031m0fkea 12 1 r2 res., chip, 200k, 1/10w, 1% 0603 vishay , crcw0603200kfkea 13 1 r3 res., chip, 100, 1/4w, 5% 1206 vishay , crcw1206100rjnea 14 1 r4 res., chip, 150k, 1/10w, 1% 0603 vishay , crcw0603150kfkea 15 1 r5 res., chip, 113k, 1/10w, 1% 0603 vishay , crcw0603113kfkea 16 1 r6 res., chip, 10k, 1/10w, 1% 0603 vishay , crcw060310k0fkea 17 1 t1 tranformer, 750311564 wurth elec., 750311564 18 1 u1 i.c. LT8302 so8e linear tech., LT8302es8e#pbf hardware: for demo board only 1 4 e1-e4 testpoint , turret, .094" pbf mill-max, 2501-2-00-80-00-00-07-0 dc2014af demo manual dc2014a
5 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. schematic diagram dc2014af demo manual dc2014a
6 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2013 lt 1013 ? printed in usa demonstration board important notice linear technology corporation ( lt c ) provides the enclosed product(s) under the following as is conditions: this demonstration board (demo board) kit being sold or provided by linear technology is intended for use for engineering development or evaluation purposes only and is not provided by lt c for commercial use. as such, the demo board herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. as a prototype, this product does not fall within the scope of the european union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations. if this evaluation kit does not meet the specifications recited in the demo board manual the kit may be returned within 30 days from the date of delivery for a full refund. the foregoing warranty is the exclusive warranty made by the seller to buyer and is in lieu of all other warranties , expressed, implied, or statutory , including any warranty of merchantability or fitness for any particular purpose. except to the extent of this indemnity , neither party shall be liable to the other for any indirect , special, incidental, or consequential damages. the user assumes all responsibility and liability for proper and safe handling of the goods. further , the user releases lt c from all claims arising from the handling or use of the goods. due to the open construction of the product, it is the user s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. also be aware that the products herein may not be regulatory compliant or agency certified (fcc, ul, ce, etc.). no license is granted under any patent right or other intellectual property whatsoever . lt c assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. lt c currently services a variety of customers for products around the world, and therefore this transaction is not exclusive. please read the demo board manual prior to handling the product. persons handling this product must have electronics training and observe good laboratory practice standards. common sense is encouraged. this notice contains important safety information about temperatures and voltages. for further safety concerns, please contact a lt c applica- tion engineer . mailing address: linear technology 1630 mccarthy blvd. milpitas, ca 95035 copyright ? 2004, linear technology corporation dc2014af demo manual dc2014a
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