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september 2007 rev 2 1/17 AN1514 application note vipower: double output buck or buck-boost converter using viper12a-e/22a-e introduction this paper introduces two double output off-line non isolated smps based on the viperx2a-e family. the first smps is a buck converter with two positive outputs and the second one is a buck-boost converter with two negative outputs. the use of viper12a-e or viper22a-e in both converters depends on the output power specifications. the power supplies are operated in off-line mode with an extended wide range of the input voltage, from 80 to 285 vac. the target applications are small loads, such as microcontrollers, motors, displays and peripherals in several industrial and home appliances. two converter topologies are introduced in this paper. the considered double output converters are based on the viperx2a-e device family and are suitable for non isolated off- line applications. viperx2a-e is a low cost monolithic smart power with a pwm controller, start-up circuit and protection integrated on the same chip. the power stage consists of a vertical power mosfet with 730 v breakdown voltage and 0.32 a for viper12a-e or 0.56 a for viper22a-e maximum drain current with internal limitation. the use of a vipower device makes the design ve ry simple and easy, since several features are integrated in the smart power ic. the first smps is a buck converter with two positive outputs and the second one is a buck-boost converter with two negative outputs. the use of viper12a-e or viper22a-e in both converters depends on the output power specifications. the power supplies are operated in off-line mode with an extended wide range of the input voltage, from 80 to 285 vac. the target applications are small loads, such as microcontrollers, motors, displays and peripherals in several industrial and home appliances with power level up to 6-8 w. www.st.com
contents AN1514 2/17 contents 1 off-line double output converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 viper application examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 double output buck converter using viper12a-e . . . . . . . . . . . . . . . . . . . . 6 2.1.1 experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 double output buck-boost converter using viper22a-e . . . . . . . . . . . . . . . 9 2.2.1 experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3 conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
AN1514 list of tables 3/17 list of tables table 1. buck converter specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 table 2. component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 table 3. load regulation at v in =80v acrms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 table 4. load regulation at v in =285v acrms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 table 5. buck-boost converter specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 table 6. component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 table 7. load regulation at v in =80v acrms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 table 8. load regulation at v in =285v acrms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 table 9. thermal characterization (package: dip8; r thj-lead =45c/w mounted by socket; t amb =25c). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 table 10. document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
list of figures AN1514 4/17 list of figures figure 1. double output buck topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 figure 2. double output buck-boost topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 figure 3. converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 4. board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 5. board prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 6. efficiency vs. output power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 7. converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 figure 8. efficiency vs. output power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 figure 9. v in =80v acrms , i out2 =75 ma, ch1=v out1 , ch2=i out1 , ch3=i lp , ch4=v out2 . . . . . . . . . . . . . 13 figure 10. v in =285v acrms , i out2 =75 ma, ch1=v out1 , ch2=i out1 , ch3=i lp , ch4=v out2 . . . . . . . . . . . . 13 figure 11. viper22a-e temperature at maximum load with parasitic capacitance . . . . . . . . . . . . . . . 13 figure 12. v ds and i d at v in =230v acrms , i out =250 ma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 figure 13. conducted emissions at full load with en55014 limits: line emissions . . . . . . . . . . . . . . . . 15 figure 14. conducted emissions at full load with en55014 limits: neutral emissions . . . . . . . . . . . . . 15
AN1514 off-line double output converters 5/17 1 off-line double output converters in these circuits the first output is obtained using the standard buck or buck-boost topology, while the second output is obtained by means of a second winding on the main inductor. this output is directly coupled with the first one in flyback mode and its value is given by the turns ratio n. the inductor is still low cost si nce a drum core can be used and the coupling between the two windings is not as critical as in a flyback converter. the electrical schematics of both configurations are shown in figure 1 and figure 2 . 2 viper application examples in this section two viperx2a-e application examples are introduced: 1. double output buck converter 24 v at 30 ma, 5 v at 50 ma 2. double output buck-boost converter (-24 v) at 250 ma, (-5 v) at 70 ma. figure 1. double output buck topology figure 2. double output buck-boost topology
viper application examples AN1514 6/17 2.1 double output buck converter using viper12a-e the proposed power supply, shown in figure 3 , is based on viper12a-e. the specifications of the converter are listed in ta b l e 1 . the input section consists of a resistor as a fuse, a single diode rectifier, and an input lc filter. such a filter provides both dc voltage stabilization and improved emi performance (compliant with en550 22 class b standard). the capacitor cin1 could be connected to provid e further reduction of conducted emi, if required. the switching frequency is 60 khz, given by the integrat ed oscillator of the viper12a-e. figure 3. converter schematic the two outputs are provided using a buck converter for the 24 v output, named "v out1 ", and a coupled inductor in flyback mode for the 5 v output, named "v out2 ". the regulation feedback is connected to "v out1 " as well as the supply circuit of the viper12a-e. doing so, only one high voltage diode and one capacitor are needed, i.e. d3 and c3 in figure 3 , reducing the complexity and the cost of the circuit. the output inductor, l, has two coupled windings on the same ferrite core, with a proper turn ratio and coupling factor in order to get the correct output voltage. in particular, 1.5 mh inductor is used, with n1=200t - wound on the ferrite core of "panasonic elc10d152e" inductor - and n2=60t. zener diodes, dz1 and dz2 protect both outputs against overvoltage. table 1. buck converter specifications parameter value ac input voltage v inac 80 - 285 vac output current i out 30 ma output current i out2 50 ma output voltage v out1 +2410%v output voltage v out2 +5 v5% switching frequency 60 khz output power ~ 1 w d 1 c 1 l v out1 c 2 gnd v out2 d 2 n d z c 3 v dd d s viper12a-e fb c 4 +24v +5v d 3 v ac d r r f c in1 c in l f r burden d z1 d z2
AN1514 viper application examples 7/17 a burden resistor is connected across v out1 in order to perform the regulation on v out2 when v out1 is in open load condition. such a resistor greatly improves the regulation with a slight impact on the efficiency. the output rectifier diodes are both fast diodes: d1 is a high voltage diode since it has to sustain a reverse voltage given by the input dc bus voltage while d2 is a low voltage diode. the part list of the proposed circuit is given in ta b l e 2 . in figure 4 the board layout is shown and figure 5 shows the lab prototype. table 2. component list reference value description r r 10 ? 1/2 w r f 10 k ? 1/4 w rburden 4.7 k ? 1/4 w c in 4.7 f, 450 v electrolytic capacitor c 1 33 f, 50 v electrolytic capacitor c 2 100 f, 16 v electrolytic capacitor c 3 1 f, 25 v electrolytic capacitor c 4 22 nf ceramic capacitor d r diode 1n4007 d 1 diode ba159 (fast) d 2 diode 1n4148 (fast) d 3 diode 1n4004 d z 22 v zener d z1 27 v zener d z2 5.6 v zener l 1.5 mh l f 470 h inductor ic1 stmicroelectronics viper12a-e
viper application examples AN1514 8/17 figure 4. board layout figure 5. board prototype 2.1.1 experimental results in this section the characterization of the circuit is given. four load conditions have been considered: 1. output1 = open load - output2 = open load 2. output1 = full load - output2 = open load 3. output1 = open load - output2 = full load 4. output1 = full load - output2 = full load in ta bl e 3 and ta b l e 4 the experimental results are listed, with 80 v and 285 v input voltage respectively. in all the considered operating conditions the proposed power supply meets the given specifications. the efficiency has been evaluated and is shown in figure 6 , where the output power p out is given by ( equation 1 ). equation 1 p out p out1 p out2 + =
AN1514 viper application examples 9/17 figure 6. efficiency vs. output power 2.2 double output buck-boost converter using viper22a-e the proposed power supply, shown in figure 7 , is based on viper22a-e. it delivers maximum 7 w output power in wide range, according to ta b l e 5 which lists the main specifications of the converter. this topology is used to supply negative output voltage referred to neutral in non isolated applications. the input stage is similar to the buck based application but requires a larger bulk capacitor due to the higher power level, as shown in ta bl e 6 . table 3. load regulation at v in =80v acrms v in =80vac v out1 (v) i out1 (ma) v out2 (v) i out2 (ma) 1 24.95 5 5.58 0 2 26.16 30 5.58 0 3 26.98 5 4.90 50 4 24.02 30 5.06 50 table 4. load regulation at v in =285v acrms v in =285vac v out1 (v) i out1 (ma) v out2 (v) i out2 (ma) 1 24.95 5 5.58 0 2 24.39 30 5.58 0 3 24.86 5 4.75 50 4 24.39 30 5.20 50
viper application examples AN1514 10/17 the two outputs are provided using a buck-boost converter for the -24 v output, named "v out1 ", and a coupled inductor in flyback mode for the -5 v output, named "v out2 ". the regulation feedback is connected to "v out1 " as well as the supply circuit of the viper22a-e. doing so, only one high voltage diode and one capacitor are needed, i.e. d2 and c3 in figure 7 , reducing the complexity and the cost of the circuit. the output inductor, l, has two coupled windings on the same ferrite core, with a proper turn ratio and coupling factor in order to get the correct output voltage. in particular, 1 mh inductor "panasonic elc08d102e" is used with a second winding (n2=45 turns) in order to obtain the secondary output. zener diode dz2 protects the out2 against overvoltage, but this protection is not needed in out1. a burden resistor (r b ) is connected across v out1 in order to perform the regulation on vout2 when vout1 is in open load condition. the output rectifier diodes are both ultrafast diodes: d3 is a high voltage diode since it has to sustain a reverse voltage given by the input dc bus voltage while d4 is a low voltage diode. the part list of the proposed circuit is given in ta b l e 6 . figure 7. converter schematic table 5. buck-boost converter specifications parameter value ac input voltage v inac 80 - 285 vac output current i out1 250 ma output current i out2 70 ma output voltage v out1 -2410%v output voltage v out2 -5 v5% switching frequency 60 khz output power ~ 7 w -e
AN1514 viper application examples 11/17 2.2.1 experimental results in this section the characterization of the circuit is given. four load conditions have been considered: 1. output1 = open load - output2 = open load 2. output1 = full load - output2 = open load 3. output1 = open load - output2 = full load 4. output1 = full load - output2 = full load the experimental results are listed in ta b l e 7 and ta bl e 8 , with 80 v and 285 v input voltage respectively. in all the considered operating conditions the proposed power supply meets the given specifications. the efficiency has been evaluated and is shown in figure 8 , where the output power p out is given by ( equation 1 ). table 6. component list reference value description r f (fuse) 10 ? 1/2 w r b 1.5 k ? 1/2 w c 1 10 f, 400 v electrolytic capacitor c 2 10 f, 400 v electrolytic capacitor c 3 10 f, 25 v electrolytic capacitor c 4 100 nf ceramic capacitor c 5 220 f,16 v electrolytic capacitor c 6 220 f,25 v electrolytic capacitor d 1 diode 1n4007 d 2 diode byt400 (fast) d 3 diode stta106 (turbosw.) d 4 diode stta102 (200v) d z1 24v zener d z2 5.6v zener l p 1mh l s 45 turns ic1 stmicroelectr onics viper22adip-e table 7. load regulation at v in =80v acrms v in =80vac v out1 (v) i out1 (ma) v out2 (v) i out2 (ma) 1 -24.72 10 - 4.85 0 2 -23.86 250 - 5.54 0 3 -24.7 10 - 4.59 70 4. -23.7 250 - 4.88 70
viper application examples AN1514 12/17 figure 8. efficiency vs. output power 2.2.2 thermal measurements due to the higher power level of such a non isolated converter, thermal constraints have to be evaluated in order to allow proper system ope ration. the main issue is related to parasitic effects that can lead to higher power dissipat ion in the device and consequently a higher working temperature. for example, if a fast diode is used, the recovery of charge generates a current spike in the device increasing the switching losses, as shown in figure 9 and figure 10 for v in =80 v and v in =285 v respectively. the device is forced to operate at high temperature as shown in figure 11 . table 8. load regulation at v in =285v acrms v in =285vac v out1 (v) i out1 (ma) v out2 (v) i out2 (ma) 1 -24.67 10 - 4.98 0 2 -24.1 250 - 5.61 0 3 -24.7 10 - 4.62 70 4 -24 250 - 5.03 70
AN1514 viper application examples 13/17 figure 9. v in =80v acrms , i out2 =75 ma, ch1=v out1 , ch2=i out1 , ch3=i lp , ch4=v out2 figure 10. v in =285v acrms , i out2 =75 ma, ch1=v out1 , ch2=i out1 , ch3=i lp , ch4=v out2 figure 11. viper22a-e temperature at maximum load with parasitic capacitance
viper application examples AN1514 14/17 in this case the temperature of the device will be so high as to enable the thermal shutdown in a few minutes. if an ultra fast diode is used under the previous load condition, thermal measurements give lower temperature as listed in ta bl e 9 . in such a case the temperature increase is below 40c increasing the efficiency of the system and allowing proper operation with ambient temperature up to 65c with no heat sink. the above considerations apply to other parasitic elements on the board, e.g. stray capacitance of the inductor, as shown in figure 12 . in this case a good in ductor helps to limit the power dissipation in the device and then the operating temperature. in figure 13 and figure 14 the emi behavior of the power supply at full load is shown, using a 50 lisn according to en550014 standard, for line and neutral respectively. although the measurements have been performed using peak detector, the emission level is well below the quasi-peak (qp) limit , complying with the previously mentioned standard. figure 12. v ds and i d at v in =230v acrms , i out =250 ma table 9. thermal characterization (package: dip8; r thj-lead =45 c/w mounted by socket; t amb =25c) v inac (vrms) pdiss (w) ? t (c) t (c) 80 0.7 30.6 55.6c 220 0.58 26.1 51.1 285 0.88 39 64c
AN1514 viper application examples 15/17 figure 13. conducted emissions at full load with en55014 limits: line emissions figure 14. conducted emissions at full load with en55014 limits: neutral emissions
conclusion AN1514 16/17 3 conclusion very low cost power supplies based on stmicroelectronics viperx2a family have been proposed for low power applications where two non isolated voltages are required. two application examples have been given with a full characterization. the converters show good performances in terms of electrical behav ior, size and cost, confirming the suitability to industrial as well as home appliance applications of such a vipower device. 4 revision history table 10. document revision history date revision changes 04-jan-2005 1 minor text changes 26-sep-2007 2 ? the document has been reformatted ? viper12a becomes viper12a-e ? viper22a becomes viper22a-e ? viper22adip becomes viper22adip-e
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