4.PWM电源介绍及故障分析

PWM电源的工作原理1.死区时间,上管下管均截止+3VALWPB++PR7711.5K_1%PC702200PPC764700PPL610UH_SPC_1205P_10012PQ26SI4810DY13487652SSGDDDDSPZD3RLZ4.3B12PR460+PC86150UF_D_6.3VPR73330PC374.7UF_1210_25VPD23BYS10-4512PR78220+PC82@150UF_D_6.3VPC364.7UF_1210_25VPC41@1000PFPC320.1UF_0805_25VPR7433.2K_1%PQ24SI480013487652SSGDDDDS+PC80@150UF_D_6.3VOUT2_DOUT2_UIM2FB2+3.3V:Ipeak=6.66A~10AVgs(PQ24)Vgs(PQ26)T0T1T2T3T4T5T0T1LowHi0VHi0VPQ26ONPQ24ONDeadTime:T0~T1,T2~T3,T4~T5(T0~T1)+3+3VALWPPQ24&PQ26TurnVALWPPQ24&PQ26Turn--off@T0~T1off@T0~T1--[1][1]此时上下管驱动信号均为低电平,两管均截止2.T1-T2时间段,上管驱动信号为高电平,下管驱动信号为低电平,此时上管导通,下管截止.公共点电压经上管D-S。向PL6流过负载,最终流向地,当电池流经电感时,在电感上产生左正右负的感应电压。+3+3VALWPPQ24VALWPPQ24--ON,PQ26ON,PQ26--OFF@T1~T2OFF@T1~T2--[2][2]B+++3VALWPIM2FB2OUT2_UOUT2_DPC364.7UF_1210_25VPQ24SI480013487652SSGDDDDSPC41@1000PFPR7711.5K_1%PQ26SI4810DY13487652SSGDDDDSPC320.1UF_0805_25V+PC86150UF_D_6.3V+PC80@150UF_D_6.3VPC374.7UF_1210_25VPZD3RLZ4.3B12PR460PC702200PPR78220PC764700PPL610UH_SPC_1205P_10012PD23BYS10-4512PR73330+PC82@150UF_D_6.3VPR7433.2K_1%+3.3V:Ipeak=6.66A~10AVgs(PQ24)Vgs(PQ26)T0T1T2T3T4T5T0T1LowHi0VHi0VPQ26ONPQ24ONDeadTime:T0~T1,T2~T3,T4~T5(T0~T1)+--3.T2-T3时间段,死区时间此时上下管驱动信号均为低电平,上下管均截止,流经电感PL6的电流突然消失,由于电感的感应效应,电感两端反产生一个反向的电压,此电压方向为右正左负Vgs(PQ24)Vgs(PQ26)T0T1T2T3T4T5T0T1LowHi0VHi0VPQ26ONPQ24ONDeadTime:T0~T1,T2~T3,T4~T5(T0~T1)+3+3VALWPPQ24&PQ26TurnVALWPPQ24&PQ26Turn--off@T2~T3off@T2~T3--[3][3]++----+3VALWPB++PR7711.5K_1%PC702200PPC764700PPL610UH_SPC_1205P_10012PQ26SI4810DY13487652SSGDDDDSPZD3RLZ4.3B12PR460+PC86150UF_D_6.3VPR73330PC374.7UF_1210_25VPD23BYS10-4512PR78220+PC82@150UF_D_6.3VPC364.7UF_1210_25VPC41@1000PFPC320.1UF_0805_25VPR7433.2K_1%PQ24SI480013487652SSGDDDDS+PC80@150UF_D_6.3VOUT2_DOUT2_UIM2FB2+3.3V:Ipeak=6.66A~10A流经电感的电流不能突变,如流经电感的电流突然消失,电感会产生反向的感应电压来抑制这个电流的减少4.T3-T4时间段,此时上管驱动为低电平,下管驱动为高电平.于是上管截止,下管导通,电感上感应出的右正左负的感应电压经过PL6的1脚过负载,过下管S-D流向电压的负端,即PL6的2脚B+++3VALWPOUT2_DIM2FB2OUT2_U+PC82@150UF_D_6.3VPC320.1UF_0805_25VPR7711.5K_1%PC374.7UF_1210_25VPC702200P+PC86150UF_D_6.3VPC41@1000PFPR460PQ26SI4810DY13487652SSGDDDDSPQ24SI480013487652SSGDDDDS+PC80@150UF_D_6.3VPL610UH_SPC_1205P_10012PR78220PC764700PPZD3RLZ4.3B12PR7433.2K_1%PR73330PD23BYS10-4512PC364.7UF_1210_25V+3.3V:Ipeak=6.66A~10AVgs(PQ24)Vgs(PQ26)T0T1T2T3T4T5T0T1LowHi0VHi0VPQ26ONPQ24ONDeadTime:T0~T1,T2~T3,T4~T5(T0~T1)+3+3VALWPPQ24VALWPPQ24--OFF,PQ26ON@T3~T4OFF,PQ26ON@T3~T4--[4][4]+--以MAX8734A为例针脚定义:1.空脚2.PGOOD输出3.ON33V开启信号4.ON55V开启信号5.ILIM33V限流调节脚6.SHDN-总开启信号7.FB33V反馈输入8.REF2V参考电压输出9.FB55V电压反馈输入10.PRO过压/欠压保护开关此脚接VCC时,关闭过压/欠压保护,及输出放电模式此脚接GND时,打开过压/欠压保护以及输出放电模式11.ILIM55V限流调节脚12.SKIP-此脚接地时工作在跳脉冲模式接VCC时工作在PWM模式接REF或悬空时工作在超声模式(跳脉冲,最小25KHZ)13.TON频率选择输入,接VCC时PWM频率为200/300KHZ接GND时工作在400/500KHZ14.BST55V自举升压15.LX55V输出相位检测脚16.DH55VPWM上管驱动17.VCCPWM核的模拟电压输入18.LDO55V线性电压输出19.DL55VPWM下管驱动20.V+电源电压输入21.OUT55V输出电压检测22.OUT33V输出电压检测23.GND模拟及功率地24.DL33VPWM下管驱动25.LDO33V线性电压输出26.DH33VPWM上管驱动27.LX33V输出相位检测脚28.BST33V自举升压脚由于IC电源芯片本身的驱动能力有限，在这样的高频率的工作条件下它不能通过DH5端直接驱动外部MOS管，所以为了提高IC的驱动能力并简化电路，几乎所有的PWM电路都采用了自举升压电路来提高驱动器的驱动能力，MAX8734在引脚BST5与LX5之间跨接了一个0.1UF的自举电容，在DH5为低电平时关闭高端驱动门驱动信号，此时下管低端驱动门驱动信号为高电平，低端驱动管（下管）导通，上管截止，下管导通，这样就把输出的LX5端强拉到地，此时，MAX8734内部本体产生的线性电压+5VALWAYSON电压通过一个二极管给自举电容充电。在高端门驱动管打开时，低端门驱动管就关闭，上管导通，下管截止，自举电容通过BST5向DH5放电，此时由于DH5的瞬间电压比输入19V电压还大，高端驱动门驱动管很快就进入饱和导通状态，这样大大提高了DH5驱动信号的驱动能力，使外部的MOS管能正常的工作。1．芯片V+VCC供电正常,2．芯片8脚输出2V参考电压3．当REF达到稳定后,LDO3上电可为外部负载提供100mA电流LDO3及LDO5均应通过一只最小4。7UF的电容旁路4．SHDN-信号为高电平5．ON3ON5电压开启信号为高电平6．DH5DL5DH3DL3开始输出PWM信号，下图所示7．自举升压电路工作，提升上管驱动信号8．反馈电路及电流检测电路工作，检测输出电压如果控制极对地短路或空焊，会烧主电源芯片，及MOS管！！！