收藏本站
IRLR/U7821CPbF
Power MOSFET Selection for Non-Isolated DC/DC Converters
P loss = P conduction + P drive + P output
( )
P loss = I rms × R ds(on)
+ ? oss × V in × f + ( Q rr × V in × f )
Control FET
Special attention has been given to the power losses
in the switching elements of the circuit - Q1 and Q2.
Power losses in the high side switch Q1, also called
the Control FET, are impacted by the R ds(on) of the
MOSFET, but these conduction losses are only about
one half of the total losses.
Power losses in the control switch Q1 are given
by;
P loss = P conduction + P switching + P drive + P output
This can be expanded and approximated by;
Synchronous FET
The power loss equation for Q2 is approximated
by;
*
2
+ ( Q g × V g × f )
? Q ?
? 2 ?
× V in × f ?
P loss = ( I rms2 × R ds(on) )
? Q gd
+ ? I × × V in ×
? i g
? ?
f ? + ? I ×
? ?
Q gs 2
i g
?
?
*dissipated primarily in Q1.
For the synchronous MOSFET Q2, R ds(on) is an im-
portant characteristic; however, once again the im-
portance of gate charge must not be overlooked since
it impacts three critical areas. Under light load the
× V in × f ?
? Q oss
? 2
?
+ ( Q g × V g × f )
+
This simplified loss equation includes the terms Q gs2
and Q oss which are new to Power MOSFET data sheets.
Q gs2 is a sub element of traditional gate-source
charge that is included in all MOSFET data sheets.
The importance of splitting this gate-source charge
into two sub elements, Q gs1 and Q gs2 , can be seen from
Fig 16.
Q gs2 indicates the charge that must be supplied by
the gate driver between the time that the threshold
voltage has been reached and the time the drain cur-
rent rises to I dmax at which time the drain voltage be-
gins to change. Minimizing Q gs2 is a critical factor in
reducing switching losses in Q1.
Q oss is the charge that must be supplied to the out-
put capacitance of the MOSFET during every switch-
ing cycle. Figure A shows how Q oss is formed by the
parallel combination of the voltage dependant (non-
linear) capacitance?s C ds and C dg when multiplied by
the power supply input buss voltage.
8
MOSFET must still be turned on and off by the con-
trol IC so the gate drive losses become much more
significant. Secondly, the output charge Q oss and re-
verse recovery charge Q rr both generate losses that
are transfered to Q1 and increase the dissipation in
that device. Thirdly, gate charge will impact the
MOSFETs’ susceptibility to Cdv/dt turn on.
The drain of Q2 is connected to the switching node
of the converter and therefore sees transitions be-
tween ground and V in . As Q1 turns on and off there is
a rate of change of drain voltage dV/dt which is ca-
pacitively coupled to the gate of Q2 and can induce
a voltage spike on the gate that is sufficient to turn
the MOSFET on, resulting in shoot-through current .
The ratio of Q gd /Q gs1 must be minimized to reduce the
potential for Cdv/dt turn on.
Figure A: Q oss Characteristic
www.irf.com
发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

*型号 *数量 厂商 批号 封装
添加更多采购

我的联系方式

*
*
*
相关PDF资料
IRLR8503TRLPBF MOSFET N-CH 30V 44A DPAK
IRLR8503TRR MOSFET N-CH 30V 44A DPAK
IRLR8715CPBF MOSFET N-CH 25V 51A DPAK
IRLS640A MOSFET N-CH 200V 9.8A TO-220F
IRLTS6342TRPBF MOSF N CH 30V 8.3A TSOP6
IRLZ14STRRPBF MOSFET N-CH 60V 10A D2PAK
IRLZ14 MOSFET N-CH 60V 10A TO-220AB
IRLZ24NSTRR MOSFET N-CH 55V 18A D2PAK
相关代理商/技术参数
IRLR7821HR 制造商:International Rectifier 功能描述:Trans MOSFET N-CH 30V 65A 3-Pin(2+Tab) DPAK 制造商:International Rectifier 功能描述:TRANS MOSFET N-CH 30V 65A 3PIN DPAK - Rail/Tube
IRLR7821PBF 功能描述:MOSFET 30V 1 N-CH HEXFET 10mOhms 10nC RoHS:否 制造商:STMicroelectronics 晶体管极性:N-Channel 汲极/源极击穿电压:650 V 闸/源击穿电压:25 V 漏极连续电流:130 A 电阻汲极/源极 RDS（导通）:0.014 Ohms 配置:Single 最大工作温度: 安装风格:Through Hole 封装 / 箱体:Max247 封装:Tube
IRLR7821TR 制造商:International Rectifier 功能描述:
IRLR7821TRHR 制造商:International Rectifier 功能描述:Trans MOSFET N-CH 30V 65A 3-Pin(2+Tab) DPAK T/R 制造商:International Rectifier 功能描述:TRANS MOSFET N-CH 30V 65A 3PIN DPAK - Tape and Reel
IRLR7821TRLHR 制造商:International Rectifier 功能描述:Trans MOSFET N-CH 30V 65A 3-Pin(2+Tab) DPAK T/R
IRLR7821TRLPBF 功能描述:MOSFET MOSFT 30V 65A 10mOhm 10nC Log Lvl RoHS:否 制造商:STMicroelectronics 晶体管极性:N-Channel 汲极/源极击穿电压:650 V 闸/源击穿电压:25 V 漏极连续电流:130 A 电阻汲极/源极 RDS（导通）:0.014 Ohms 配置:Single 最大工作温度: 安装风格:Through Hole 封装 / 箱体:Max247 封装:Tube
IRLR7821TRPBF 功能描述:MOSFET 30V 1 N-CH HEXFET 10mOhms 10nC RoHS:否 制造商:STMicroelectronics 晶体管极性:N-Channel 汲极/源极击穿电压:650 V 闸/源击穿电压:25 V 漏极连续电流:130 A 电阻汲极/源极 RDS（导通）:0.014 Ohms 配置:Single 最大工作温度: 安装风格:Through Hole 封装 / 箱体:Max247 封装:Tube
IRLR7821TRRHR 制造商:International Rectifier 功能描述:Trans MOSFET N-CH 30V 65A 3-Pin(2+Tab) DPAK T/R