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6.4

BOM reduction

As explained in

Section 3.1 Startup

, low side bridge diodes are useful only during the PFC output capacitor

precharge startup phase. Therefore, you can remove one low side diode to reduce the bill of materials. However,
this modification results in doubling the PFC output capacitor precharge duration, as shown in the figure below.

Figure 24.

Low side diode removal influence on PFC output cap charge time

UM2948

BOM reduction

UM2948

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Rev 1

page 17/28

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Содержание STEVAL-SCR002V1

Страница 1: ...reliability of the power converter it is necessary to limit this inrush current The STEVAL SCR002V1 evaluation board introduces a simple and innovative AC DC front end circuit The bridge rectifier consists of diodes and silicon controlled rectifiers SCRs that are implemented in the bridge low side An uninsulated power supply and a few SMD discrete components make the design very compact The board ...

Страница 2: ...nic systems The board has to be connected directly on the mains Non isolated parts at high voltage levels are present on both sides of the PCB The high current flowing through the two SCRs generates heat the board temperature can reach up to 150 C at full power Be aware that due to thermal inertia the board could remain hot even after current has ceased to flow Work area safety The work area must ...

Страница 3: ...ise EN55014 and EN55022 solution 1 3 Circuit and purpose The STEVAL SCR002V1 purpose is to bypass the NTC via the SCRs The SCR driver consists of a triac and two diodes At system startup inrush current is limited by the NTC see Section 3 1 When the DC capacitor is fully charged the MCU turns the SCR driver on to bypass the NTC see Section 3 2 Thanks to the innovative arrangement of the SCR gate dr...

Страница 4: ...onents STEVAL SCR002V1 pinout EN enable pin The NTC is bypassed as long as the enable pin is supplied with a positive voltage from 3 3 to 15 V GND_DC DC voltage reference LINE AC line voltage NEUTRAL AC neutral voltage DC DC high voltage The following figure shows a connection example of the STEVAL SCR002V1 to a standard PFC with inrush managed via relay UM2948 Connection and startup UM2948 Rev 1 ...

Страница 5: ...Figure 4 Connection example of the STEVAL SCR002V1 to a boost converter PFC relay replacement UM2948 Connection and startup UM2948 Rev 1 page 5 28 ...

Страница 6: ...netic interference reduction and a faster response to line dips Moreover this bypass solid state solution has no moving parts preventing from spark and contact arcing that are the root cause of the reduction of the electromechanical relay lifetime Solid state topologies with SCRs allow applications to comply easily with the following standards IEC61000 3 3 voltage fluctuations and flicker in publi...

Страница 7: ...e polarity TN1605H 6T X1 or X2 turns on and off alternately and automatically according to the AC line polarity In nominal operation mode the two top diodes of the rectifier bridge D3 and D4 and the two SCRs X1 and X2 rectify the AC line the inrush resistor is then bypassed Figure 8 Steady state PFC on bypass on 3 3 SCR gate driver with automatic switching operation One issue of SCR bypass topolog...

Страница 8: ... the positively biased SCR X1 is turned on The nominal current flows through the D3 diode the PFC output stage and X1 During this AC positive half sine wave D2 cathode to anode voltage is negative VAK_D2 0 D2 diode is blocked No current can flow through the X2 gate and consequently the SCR X2 remains blocked as long as it is reversed biased Thanks to the SCR gate driver topology the nonconducting ...

Страница 9: ...de SCR bypass solution 4 1 Power efficiency To perform the efficiency test we used an electronic load from 10 to 100 of the total admissible power The figure below shows the results which demonstrate the low side SCR bypass topology has no impact on the total power losses and efficiency results Thus the SCR power losses with their control circuits have the same power losses of the electro mechanic...

Страница 10: ... between line and ground and one between neutral and ground For each coupling we applied bursts to positive and negative polarities We achieved the same IEC61000 4 4 withstanding level with the original configuration using a relay and an NTC The low side bypass SCR solution has no impact on the burst immunity system performance Table 1 IEC61000 4 4 test results for the STEVAL SCR002V1 Coupling Min...

Страница 11: ...ases for negative surge test results at the peak line voltage B configuration Phase 1 before the surge is applied the nominal current flows through the SCR_N positively biased Phase 2 applying a negative surge the AC main voltage VLN becomes negative and the SCR_N is negatively biased The SCR_N turns off and the SCR_L handles the surge current becoming positively biased The TN1605H 6T is specified...

Страница 12: ... the surge test at 0 phase angle Figure 18 Waveforms resulting from the 2 kV IEC61000 4 5 test C and D configurations During the IEC 61000 4 5 lightning surge test the triac diodes and SCR measured values are within the specified values Components stay in a safe operating area during the 2 kV IEC61000 4 5 surge test UM2948 Surge robustness UM2948 Rev 1 page 12 28 ...

Страница 13: ...19 SCR current waveform Referring to AN533 the dissipated power corresponding to this half wave can be calculated as follows Pdis VTO IT av RD ITRMS 2 where IT av IP π and ITRMS IP 2 VTO and RD respectively correspond to the threshold voltage and the dynamic resistance The following tables are extracts from the TN1605H 6T data sheet Table 2 Static electrical characteristics Symbol Test conditions ...

Страница 14: ...60 C Load power 1000 W VAC 230 VRMS 50 Hz Ip 2 1000 230 6 15A Pd 1 84W At P 1000 W the maximum case temperatures measured are 125 C and 130 C on the SCR and the bridge diode Table 4 Maximum case temperatures for SCR and bridge diode Case temperature SCR Bridge diode Tc C 125 130 Tj C 127 145 Guard band Good Low UM2948 Temperature measurements UM2948 Rev 1 page 14 28 ...

Страница 15: ... for P 0 75 W 3 3 47 35 0 0 058 OK P 0 75 W N A 4 42 6 0 085 5 53 2 0 133 6 63 8 0 191 6 8 72 3 0 246 7 74 5 0 261 8 85 1 0 340 9 95 7 0 431 10 106 4 0 532 11 117 0 0 644 12 127 7 0 766 NOK PWM recommended 0 98 13 138 3 0 899 0 83 14 148 9 1 043 0 72 15 159 6 1 197 0 63 Table 6 Operation with gate resistor values adapted to fit Ig 35 mA EN_supply voltage V R1 R2 values to fit Ig 35 mA Required pow...

Страница 16: ...pply the MCU before charging the DC output capacitor In this way the MCU can ensure the inrush current limiter soft start Note that most of the applications have a standby mode so the MCU is already supplied through its own auxiliary power supply Figure 22 Low side ICL topology as a mixed bridge In the mixed bridge topology SCRs are controlled in phase angle to increase smoothly the PFC output cap...

Страница 17: ...arge startup phase Therefore you can remove one low side diode to reduce the bill of materials However this modification results in doubling the PFC output capacitor precharge duration as shown in the figure below Figure 24 Low side diode removal influence on PFC output cap charge time UM2948 BOM reduction UM2948 Rev 1 page 17 28 ...

Страница 18: ...to positively biased SCR Easy to drive Single ENABLE pin Can be driven from MCU SCR gates self powered by AC line Relay existing control can be used to drive the SCR bypass PWM gate signal allows reducing driver power consumption Easy to implement TO220AB SCR tab can be put on the same heatsink without insulated transfer interface material SMD packages available for SCRs Only few SMD components us...

Страница 19: ...8 Board layout Figure 25 STEVAL SCR002V1 top side layout Figure 26 STEVAL SCR002V1 bottom side layout UM2948 Board layout UM2948 Rev 1 page 19 28 ...

Страница 20: ...EVAL SRC002V1 circuit schematic A T filter R1 C1 R2 is placed on top of the Z0110MN gate to maximize the EFT immunity of the low side ICL driver Refer to AN5649 for further information UM2948 Schematic diagrams UM2948 Rev 1 page 20 28 ...

Страница 21: ... diode ST STTH110A 4 1 NTC1 22 R NTC Any Any 5 1 Q1 Z0107MN 5AA4 SOT 223 1 A standard triac ST Z0107MN 5AA4 6 2 R1 R2 47 R 5 0 75 W 1206 Resistors Any Any 7 4 TP1 TP2 TP3 TP4 20 2136 Test points VERO 20 2136 8 2 X1 X2 TN1605H 6T TO 220AB High temperature 16 A SCRs ST TN1605H 6T 9 1 HE9TF L 35 mm 1 m x 3 4 inches x 3 4 inches x 1 8 inches Heat sink Any Any 10 3 M3x8 mm CHC screw Any Any UM2948 Bill...

Страница 22: ...tic diagrams Bill of materials STEVAL SCR002V1A 1 STEVAL SCR002V1A schematic diagrams STEVAL SCR002V1A bill of materials 1 This code identifies the STEVAL SRC002V1 evaluation board first version It is printed on the board PCB UM2948 Board versions UM2948 Rev 1 page 22 28 ...

Страница 23: ...ntal authorization under part 5 of this chapter 3 1 2 Notice for Innovation Science and Economic Development Canada ISED For evaluation purposes only This kit generates uses and can radiate radio frequency energy and has not been tested for compliance with the limits of computing devices pursuant to Industry Canada IC rules À des fins d évaluation uniquement Ce kit génère utilise et peut émettre d...

Страница 24: ...Revision history Table 8 Document revision history Date Revision Changes 04 Jul 2022 1 Initial release UM2948 UM2948 Rev 1 page 24 28 ...

Страница 25: ...3 EMC immunity 10 4 4 Surge robustness 11 5 Thermal management 13 5 1 Dissipated power 13 5 2 Temperature measurements 14 6 Board possible modifications 15 6 1 Gate resistors 15 6 2 PWM driver control 16 6 3 Soft start solution 16 6 4 BOM reduction 17 7 Topology sum up 18 8 Board layout 19 9 Schematic diagrams 20 10 Bill of materials 21 11 Board versions 22 12 Regulatory compliance information 23 ...

Страница 26: ...ermal resistance 13 Table 4 Maximum case temperatures for SCR and bridge diode 14 Table 5 Operation with original gate resistor fixed values 15 Table 6 Operation with gate resistor values adapted to fit Ig 35 mA 15 Table 7 STEVAL SCR002V1 versions 22 Table 8 Document revision history 24 UM2948 List of tables UM2948 Rev 1 page 26 28 ...

Страница 27: ...tandard validation average measurement VAC 230 V 50 Hz P 1000 W 10 Figure 14 Test schematic and waveform specification for IEC61000 4 4 10 Figure 15 IEC61000 4 5 surge test configuration 11 Figure 16 Waveforms resulting from the 2 kV IEC61000 4 5 test A configuration 11 Figure 17 Waveforms resulting from the 2 kV IEC61000 4 5 test B configuration 12 Figure 18 Waveforms resulting from the 2 kV IEC6...

Страница 28: ...ts and ST assumes no liability for application assistance or the design of purchasers products No license express or implied to any intellectual property right is granted by ST herein Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product ST and the ST logo are trademarks of ST For additional information about ST...

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