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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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IRF7831PBF датащи(PDF) 8 Page - International Rectifier |
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IRF7831PBF датащи(HTML) 8 Page - International Rectifier |
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8 / 10 page  IRF7831PbF 8 www.irf.com 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 = Pconduction+ Pswitching+ Pdrive+ Poutput This can be expanded and approximated by; P loss = Irms 2 × R ds(on ) () + I × Q gd i g × V in × f ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ + I × Q gs2 i g × V in × f ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ + Q g × Vg × f () + Q oss 2 ×V in × 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 Qgs2, 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) capacitances C ds and Cdg when multiplied by the power supply input buss voltage. Synchronous FET The power loss equation for Q2 is approximated by; P loss = Pconduction + Pdrive + Poutput * P loss = Irms 2 × R ds(on) () + Q g × Vg × f () + Qoss 2 ×V in × f ⎛ ⎝ ⎜ ⎞ ⎠ + Q rr × Vin × f ( ) *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 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/Qgs1 must be minimized to reduce the potential for Cdv/dt turn on. Power MOSFET Selection for Non-Isolated DC/DC Converters Figure A: Q oss Characteristic |
Аналогичный номер детали - IRF7831PBF |
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Аналогичное описание - IRF7831PBF |
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