EVBUM2125 - NCP1052GEVB Low-Cost 100 mA High
Contents
1. 12 V 100 mA NCP1052 Buck Demo Board As shown in Figure 10 a 2 inch by 1 5 inch small surface mount demo board of 12 V 100 mA buck is presented The design is made on a single sided board The ON Semiconductor Wna bill of material is shown in Table 2 The component symbols http www onsemi cam A _ are those in Figure 2 In order to have sufficient startup NCP1052 buck demo board ability the Vcc capacitor is 6 8 uF which gives a 3 4 ms fault cee oe MOBE eee sampling time Because of this feature the circuit enters Input 85 to 265 Vac Output 12V 100mA fault mode when output current exceeds 200mA after startup as shown in Figure 11 b The efficiency of the circuit is typically 65 at 100 mA Figure 10 Layout of the Demo Board Table 1 BILL OF MATERIAL FOR NCP1052 EVALUATION BOARD Switching Regulator 300 mA NA SOT 223 ON NCP1052ST136T3G 136 kHz Semiconductor Ultrafast Diode 1 A 600 V NA SMB ON MURS160T3G Semiconductor Switching Diode 200 mA 100 V NA SOD 123 ON MMSD914T1G Semiconductor A M O D3 1 General Diode 1A 600V N SMA N MRA4005T1G No Yes No Yes Substi Toler Manufacturer Part tution Description Value ance Allowed Semiconductor MMSZ6V8T1G ZA 1 Zener Diode 5 SOD 123 ON Semiconductor Z2 1 S ON 12V Zener Diode 6 8 V 5 OD 123 Semiconductor R1 1 Chip Resistor 2 kQ 125 mW 5 0805 Vishay CRCW08052001FN Yes Yes EA C 1 Tantalum Capacitor 220 uF 16V 10 CODE R Vishay Sprague 52. A typical example is shown in Figure 12 In higher output current application the load regulation is the major problem The 5 1KQ resistor plays an important role for the load regulation The primary output voltage is higher than the secondary because it can increase the output current ability by stepping up the current in the transformer The line regulation is shown in Figure 13 when the output currents are constant MUR160 5 1k Le 1uF MUR160 24V 200mA as 7 GND 1 2mH 92 3uH 220uF MUR160 5V 150mA Figure 12 Dual Output Buck boost www BD FiEtcom ON NCP1052GEVB 0 Test Procedure 1 Connect the output terminals of the demo board to 5 a 12 V 100 mA load The load can be made by ten S paralleled 1 4 Watt axial 120 Q resistors The load D can also be an electronic load 10 R 12V 01A 1 2Q z Power 12 V x 0 1 A 1 2 W 2 Connect a voltmeter or oscilloscope to monitor the output voltage 5 Er 3 Apply an 85 to 265 V AC source to the input terminal of the evaluation board to check 1f there is output voltage of 12 V or not AO 100 150 200 250 300 INPUT VOLTAGE Vac Figure 13 Line Regulation of the Dual Output Buck boost CONCLUSION 100 mA high voltage low cost buck and buck boost circuits using NCP1052 are presented These circuits are designed for cost saving non isolated application so that optocoupler and transformer are saved The possible input voltage range is from 20 Vdc to 700 Vdc so
3. lt 700 V lt 700 Vout V lt lt 700 V It depends on transformer ratio lt 700 V Operating mode in nominal Continuous Continuous Discontinuous condition Standby ability on Vcc charging Bad The current flows through Good The current passes Good The current passes current output even if there is no load through inductor only through primary winding only Transformer Auxiliary winding It is only for standby It is only for standby improvement or additional improvement or additional output output It is a must for the main output Additional auxiliary winding can improve standby performance Isolation Yes Opto coupler can be eliminated if isolation is not needed www BD t ctom ON NCP1052GEVB Burst mode Operation The NCP1052 is with a burst mode control method It means the MOSFET can be completely off for one or more switching cycles The output voltage is regulated by the overall duration of dead time or non dead time over a number of switching cycles This feature offers advantages on saving energy in standby condition since it can reduce the effective duty cycle dramatically In flyback topology the circuit is mainly designed for discontinuous conduction mode DCM in which the inductor current reaches zero in every switching cycle The DCM burst mode waveform can be represented in Figure 5 It is similar to the pulse width modulation PWM one AA AA Burst mode AAAAAAA PWM Figu
4. almost 0 V in this moment In buck boost the potential of the IC reference ground pin S becomes Vout in this moment The voltage in C will be charged to the output voltage On the other hand when main switch is closed and the diode D is opened diode D4 is reverse biased by a voltage with magnitude Vin and Vint Vout respectively Hence D does not affect the normal operation of the buck and buck boost converter It is noted that the instantaneous voltage in C4 can be possibly greater than the output voltage especially when output current or output ripple is too large It directly affects the load regulation of the circuit since the IC regulates the output voltage based on the voltage in C4 In order to solve it larger values of L and Ry can help to slow down the charging speed of C4 It reduces the maximum instantaneous voltage in C4 so that output voltage at high output current can be pulled up and a good regulation is made Larger value of L can help the load regulation but it usually unwanted because it is bulky Hence resistor R4 is recommended Larger value of Ry makes higher output voltage Hence it is called as a pull up resistor and it can help to pull up the output voltage slightly The voltage in C representing the output voltage is feedback to the feedback FB pin of the NCP1052 through www BD t ctom ON NCP1052GEVB a diode D2 and zener diode Z2 When output voltage is too high there will be a grea
5. that it is suitable for general AC DC and DC DC applications with positive or negative output voltages It is noted that the standby ability charging current However it can be improved by adding an auxiliary winding to the Vcc The design consideration of each component in the circuits is explained By replacing the NCP1052 with NCP1055 the output current can be increased By adding an auxiliary winding multi output can be obtained A 12 V 100 mA demo board is presented with typical 65 efficiency of the circuits is not good because of the Vcc capacitor ON Semiconductor and uD are registered trademarks of Semiconductor Components Industries LLC SCILLC SCILLC owns the rights to a number of patents trademarks copyrights trade secrets and other intellectual property A listing of SCILLC s product patent coverage may be accessed at www onsemi com site pdf Patent Marking pdf SCILLC reserves the right to make changes without further notice to any products herein SCILLC makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does SCILLC assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability including without limitation special consequential or incidental damages Typical parameters which may be provided in SCILLC data sheets and or specifications can and do vary in different applications a
6. 94D227X9016R2T Yes Yes C1 1 Ceramic Capacitor 0 22 uF 25 V 10 1206 Vishay VJ1206Y224KXXAT Yes Yes 1 Tantalum Capacitor 6 8 uF 16V CODE A Vishay Sprague 595D685X9016A2T Yes Yes 1 Yes Aluminium 400 V 10 uF 2 Through Rubycon 400WA10M12 5X16 Yes Electrolytic hole as Capacitor surface mount L 1 Surface Mount 680 uH 20 Special Cooper UP2B 681 R Yes Yes Power Inductor 355 mA www BD t 7ctom ON NCP1052GEVB st l mM Lu H a A H r a y A Vin 300 Vdc m D O OUTPUT CURRENT mA a Load Regulation 3 gt O Z LH O LL LL Lu 0 50 100 150 200 250 300 OUTPUT CURRENT mA b Efficiency Figure 11 12V 100mA Buck Performance 1N4005 1N4746 NCP1 ie 00 1N4005 22uF Universal 10uF AC Input Dual Output Buck boost with Increased Output Current Capability Replacing NCP1052 by NCP1055 which is with a current limit of 680 mA the output current capability is increased Larger value of inductor L is selected for high current On the other hand the current consumption of NCP1055 is higher than NCP1052 and the startup transient time is longer in a higher power application Hence the Vcc capacitor is increased When the Vcc capacitor increased its charging frequency is decreased Output capacitor is also needed to be increased to reduce this lower frequency charging current ripple In addition by adding one more auxiliary winding to the inductor a secondary output is made
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8. NCP1052GEVB Low Cost 100 mA High Voltage Buck and Buck Boost Using NCP1052 Evaluation Board User s Manual Introduction This application note presents low cost high voltage 100 mA non isolated power supply using NCP1052 by buck and buck boost topology The NCP1052 is one of the latest low cost switching controllers with integrated 700 V 300 mA power switch from ON Semiconductor It is primarily designed for isolated 10 W range flyback converter If isolation is not needed the IC can also be used as stepping down buck and buck boost converter for further cost saving by removing optocoupler and replacing the transformer by an inductor The output current capability is 100 mA The possible operating range is from input range between 20 Vdc and 700 Vdc to output range of 5 0 V or above with 100 mA Typical efficiency around 65 is obtained in the 12 V buck demo board Advantages of the proposed circuits include Comparing to flyback buck and buck boost eliminates optocoupler and replaces transformer by an inductor for cost saving Buck and buck boost offers smaller voltage stress in switches comparing to flyback It minimizes the switching loss and increases efficiency e NCP105x can power up itself from the high input voltage with wide range between 20 Vdc and 700 Vdc It needs no extra supply circuit e NCP105x operates at 44 100 or 136 kHz and accommodates low cost components such as aluminum electrol
9. about 1 mA Hence the saturation current of the inductor L is needed to be bigger than their sum Another consideration on the inductor is the low pass filtering capability for the Vcc hysteresis low frequency and the 50 60 Hz rectified AC line voltage ripple As shown in Figure 3 there is a low frequency charging current with magnitude 6 3 mA flowing through the inductor and causes low frequency ripple in the output voltage A higher value of the inductance can help to reduce the output ripple It is noted that when the output power is higher the startup time becomes longer It needs bigger Vcc capacitor and makes lower Vcc charging frequency As a result a bigger inductance is needed The last consideration is the effect of load regulation Large inductor can limit the inrush current flowing into capacitor C4 as shown in Figure 4 High inrush current is not desirable because it can make the C1 voltage higher than the output voltage It makes load regulation poor If there is no pull up resistor R4 inductor value L is chosen to be as large as possible say 2 mH Output Capacitor Because of the burst mode characteristic and the low frequency Vcc charging current the output ripple is larger than those in PWM Hence a relatively bigger output capacitor is needed to keep output ripple small However big output capacitor needs a long time to build up the output voltage initially and hence the circuit may enter into fault mode in the s
10. ed that when R pulls up the output voltage at a given output current condition the output voltages at lower output current conditions are also pulled up Hence the clamping zener diode Z4 is needed to be with the breakdown voltage as same as the output voltage but it will reduce some of the efficiency at lower output current conditions DESIGN CONSIDERATION Topology Buck circuit is to step down a voltage Buck boost circuit is to step up or down a voltage The output voltage is inverted The maximum duty of NCP1052 is typically 77 Because of burst mode control the effective maximum duty is lower and said to be 70 roughly When a buck converter is in continuous conduction mode CCM the input voltage Vin and output voltage Vout are related by the duty ratio D Vout _ p lt 97 eq 2 The relationship in buck boost is Vout D 07 _ eq 3 Val I 1207 Another aspect on topology is the output current The maximum output current is always smaller than the maximum switch current in non isolated topologies However in isolated topologies such as flyback the maximum output current can be increased by a transformer Table 1 Summary of Topology Difference Using NCP1052 Output voltage Negative amp lt 2 33 Vin Depending on transformer ratio Output current lt lt 300 mA output current is lt 10 W It depends on operating only a portion of the inductor condition and audible noise level current Input voltage
11. ering features to minimize EMI and short circuit fault timing function Do Lo Di R4 Input C3 Output Input Output b Buck boost Figure 2 Proposed Circuit Using NCP1052 In Figure 3a it is noted that in the buck topology the input voltage powers up the IC through the path across the inductor L and capacitor C This charging path passes through the output and a low frequency ripple will be found in the output voltage Hence the value of C gt is needed to be small enough to increase this charging frequency fycc in order to reduce output voltage ripple because some efficiency is lost due to this low frequency ripple Output b Buck boost Figure 3 Charging Current of C gt In Figure 3b it is noted that in the buck boost topology the charging current path is blocked by diode D and hence the charging of C2 does not affect the output voltage directly However it still affects the output voltage indirectly and Slightly by adding some low frequency noise on the inductor Hence small value of Co is also wanted b Buck boost Figure 4 Output Voltage Couples to C4 witha Charging Current The function of diode D4 capacitor C4 and resistor R4 are to transfer the magnitude of output voltage to a voltage across C4 so that the IC can regulate the output voltage In Figure 4 when the main switch inside the IC is opened and the diode D is closed In buck the potential of the IC reference ground pin S becomes
12. gned for universal ac input voltage 85 to 265 Vac the rectified input voltage will be possibly as high as 375 Vdc In order to keep the 4 us condition the inductance value will be 5 mH by 5 and 6 For buck di _ Vin Vout Vin eq 5 dt L L For buck boost di _ Vin eq 6 dt L The 5 mH is practically too high and hence not very practical Therefore the inductor is basically selected by market available inductor models which is with a normally smaller inductance but not too small It must have enough saturation current level gt 300 mA If inductance is too small the di dt becomes too high and the NCP1052 will have a very high current limit effectively because there is a propagation delay typically 135 ns to turn off the switch The current flowing through the inductor L includes three parts First there is a Vcc charging current Istart in Figure 3 It happens when Vcc needs charging Its magnitude is 6 3 mA It is noted that the Vcc discharging current does not flow through the inductor Second it is the main inductor current to deliver the output current It is noted that the peak of burst mode inductor current is higher than PWM one as in Figure 6 for the same level of averaged inductor current or output current Finally there is a current flowing through diode D4 to charge up C4 It also flows through the inductor as shown in Figure 4 Its magnitude is a greater than SOUA current and practically it is
13. load condition The relationship between zener voltage and output voltage is shown in 1 Higher value of R4 helps to pull up the output voltage higher by reducing the charging rate of the buffering capacitor C4 Standby Condition The standby ability of the proposed buck converter is not good It is because there is a Vcc charging current Istart flows through the output capacitor in Figure 3 a This charging current is a low frequency pulsating signal As a result the voltage in the output capacitor continuously rises up by the charging current pulses In order to prevent over voltage in the output capacitor the zener Z4 absorbs the charging current It consumes main portion of energy in standby The proposed buck boost is better in term of the standby ability It is because the Vcc charging current in Figure 3 b www BD t lt ctom ON NCP1052GEVB only passes through the inductor The charging current pulses become an averaged energy stored in the inductor and consume smaller amount of power comparing to the buck case a Buck b Buck boost Figure 8 Auxiliary Winding to improve standby Abillity The auxiliary winding to supply the Vcc voltage in Figure 8 is a method to improve the standby ability The auxiliary winding keeps the Vcc voltage above 7 5 V and disable the Vcc charging current and hence its standby loss The auxiliary winding is coupled from the inductor L with polarity same as the regulated o
14. nd actual performance may vary over time All operating parameters including Typicals must be validated for each customer application by customer s technical experts SCILLC does not convey any license under its patent rights nor the rights of others SCILLC products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application Buyer shall indemnify and hold SCILLC and its officers employees subsidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part SCILLC is an Equal Opportunity Affirmative Action Employer This literature is subject to all applicable copyright laws and is not for resale in any manner PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT Literature Distribution Center for ON Semiconductor P O Box 5163 Denver Colorado 80217 USA Phone 303 675 2175 or 800 344 3860 Toll Free US
15. re 5 DCM Inductor Currents in Burst Mode and PWM Control In non isolated topologies such as buck or buck boost the circuits are mainly designed for CCM The CCM burst mode waveform is different to the PWM waveform in Figure 6 Because of this characteristic burst mode requires a higher peak value of the inductor current in order to have the same level of averaged inductor current or output current Burst mode PWM Figure 6 CCM Inductor Currents in Burst Mode and traditional PWM Control As shown in Figure 5 and 6 burst mode control produces low frequency waveform comparing to the switching frequency Part of the power loss in this low frequency becomes audible noise Therefore burst mode control is not suitable for high power applications such as more than 20 W Vcc Capacitor The Vcc capacitor C2 is the key component to make the circuit operate in normal mode or fault mode The device recognizes a fault condition when there is no feedback current in the FB pin during the time from Vcc 8 5 V to 7 5 V The Vcc capacitor directly affects this time duration In normal mode the Vcc follows a 8 5 V 7 5 V 8 5 V hysteresis loop When the circuit is in fault mode the Vcc follows a 8 5 V 7 5 V 4 5 V 8 5 V hysteresis loop The device keeps its MOSFET opened except for the time from Vcc 8 5 V to 7 5 V and delivers a little amount of power to the output in fault mode A common and extreme case to enter fault condition is the
16. startup The MOSFET begins switching at the Vcc is firstly charged to 8 5 V and hence output voltage rises The output voltage needs some time to build up the output voltage from 0 V to a desired value When the desired level is reached a feedback current flows into the device to stop its switching If the feedback current is determined before Vcc reaches 7 5V the circuit will remain in normal mode Otherwise the circuit will enter the fault mode and cannot provide the output voltage at its desired level Therefore the Vcc capacitor is needed to be big enough to ensure sufficient time for Vcc going from 8 5 V to 7 5 V to sample feedback current in startup Vout Voc FB current Cd Ld z time Output waveforms with big enough Vcc capacitor Desired level of Vout Output waveforms with too small Vcc capacitor Figure 7 Startup Scenarios of the Circuits with Big Enough or Too Small Vcc Capacitor Practically the NCP1052 consumes approximately 0 5 mA in normal operation The concerned fault sampling time for feedback signal is from 8 5 V to 7 5V Hence www BDF t ctom ON NCP1052GEVB C i 0 5 x 10 8 sampling time ead 0 5 x 10 3 sampling time For example if sampling time or startup transient is designed to be 20 ms 10 UF Vcc capacitor is needed Inductor The 300 mA current limit in the NCP1052 is measured with a condition that the di dt reaches 300 mA in 4 us When the buck or buck boost circuit is desi
17. tartup in Figure 7 Buffering Capacitor Buffering capacitor C3 is to provide a greater than 50 LA to the feedback pin of NCP1052 It is relatively much smaller than the output capacitor because the current consumption in this capacitor is much smaller and the output voltage cannot copy to this buffering capacitor if the buffering capacitor voltage is higher than the output voltage Diodes D and D4 are recommended to be the same part for compatibility in speed and voltage drop It helps the voltage in the capacitor C4 to be similar to the output voltage The reverse blocking voltage of D and D4 is needed to be large enough to withstand the input voltage in buck and input voltage plus output voltage in buck boost respectively D gt is not a critical component Its function is to make sure that feedback current is only in one direction The accuracy of its voltage drop used in 1 is not important since the 4 3V reference voltage in the NCP1052 is loosely set Zener Diodes Z1 is to clamp the output voltage when there is light load or no load Hence the accuracy of Z4 helps the regulation accuracy in the light load or no load condition It is also the main component to consume energy when the circuit is in no load condition The output voltage is clamped and hence the output capacitor is protected Zz and R are to set the output voltage at the nominal load current Hence their accuracy affects the regulation accuracy at the nominal
18. ter than 50 uA current inserting into the feedback pin of the NCP1052 The NCP1052 will stop switching when it happens When output voltage is not high enough the current inserting into the feedback is smaller than 50 uA The NCP1052 enables switching and power is delivered to the output until the output voltage is too high again The purpose of the diode D gt is to ensure the current is inserting into the feedback pin because the switching of NCP1052 can also be stopped when there is a greater than 50 uA current sinking from the FB pin The purpose of the zener diode Zz is to set the output voltage threshold The FB pin of NCP1052 with a condition of 50 uA sourcing current is about 4 3 V The volt drop of the diode D gt is loosely about 0 7 V at 50 uA Hence the output voltage can be loosely set as follows Vout zener 4 3 V 0 7 V eq 1 zener 5V ey According to 1 the possible minimum output voltage of the circuit is 5 0 V when there is no zener diode Z2 If there is no load the IC will automatically minimize its duty cycle to the minimum value but the output voltage is still possible to be very high because there is no passive component in the circuit try to absorb the energy As a result output voltage will rise up dramatically and burn the output capacitor eventually Hence a zener diode Z4 or minimum dummy load resistor is needed to consume the minimum amount of energy as shown in Figure 2 It is also not
19. utput voltage The Vcc voltage in the auxiliary winding is designed to be between the normal Vcc limits of 7 5 and 8 5 V typically The frequency jittering feature loses when the Vcc voltage is fixed When output is shorted there will be no voltage coming from the auxiliary winding and the circuit will enter fault mode with the 4 5 V 8 5 V 7 5 V 4 5 V hysteresis loop Another method to supply the Vcc voltage is coupling capacitor technique in Figure 9 The output voltage is coupled to the inserted capacitor when the diodes are closed The voltage drop of the diodes compensate each other Hence the diode voltage drop effect can be neglected The NCP1052 needs a nominal Vcc voltage of 8V The inserted resistor consumes some voltage from the output voltage Vout to make a 8V to the Vcc pin Based on the 0 5mA typical current consumption of Vcc pin The inserted resistance value is Vout 8 0 5 KQ a Buck I b Buck boost Figure 9 Coupling Capacitor Technique to Improve Standby Abillity Temperature Rise The NCP1052 is a very compact package with the control circuit and high voltage power switch Its typical on resistance is 22 Q Temperature rise exists It is recommended to design the PCB board with a large copper area next to the device as a heatsink This heatsink decreases the temperature rise and reduces the on resistance Finally the efficiency of the circuit is benefited www BD FiEtcom ON NCP1052GEVB EXAMPLES
20. ytic capacitors and powered iron core magnetic e NCP105x offers frequency jittering for reduced electromagnetic inference EMI e NCP105x offers thermal and short circuit fault protection Simple design as no control loop compensation is concerned ON Semiconductor http onsemi com EVAL BOARD USER S MANUAL The proposed buck and buck boost converters are very similar to each other Their major difference is that buck provides a positive output voltage but buck boost provides a negative output voltage referring to the input ground Figure 1 Evaluation Board Photo Principle of Operation Figure 2 shows the proposed buck and buck boost converters The rectifier circuit which consists of capacitor C3 and diode D3 is in the front end for AC or DC input voltage Then the NCP1052 is self powered up from the rectified input voltage directly with a Vcc capacitor Co When the switch inside the IC is opened there is a voltage across Drain D and Source S pins of the IC If this voltage is greater than 20 V an internal current source Istart 6 3 MA typ inside the IC charges up C2 and a voltage in C3 is built up for the operation of the IC Comparing to the switching Semiconductor Compon i 1 blication Order Number June 2012 Rev WWW P CO m EVBUM2125 D NCP1052GEVB frequency the Vcc voltage level is in a lower frequency 7 5 8 5 V hysteresis loop This Vcc hysteresis loop is for frequency jitt
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