Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
[5-1] Mor M. Peretz, Switch-Mode Power Supplies Parasitic effects Snubbers and clamps • Turn on and turn off effects • Turn on - diode reverse recovery • Turn off – dI/dT effect on transistor • Turn off – diode forward recovery • Mosfet gating • Transistor protection - Clamp • Flyback leakage problem • Clamp configuration • Component selection • Diode protection – Snubber • Switching snubbers and lossless (ZVS) snubber [5-2] Mor M. Peretz, Switch-Mode Power Supplies Diodes reverse recovery L Vin Vx Vo R C Diode on – bidirectional current flow Mor M. Peretz, Switch-Mode Power Supplies Diodes recovery – spike and oscillations Diode on Lstray Lstray ESR Lstray Diode off Lstray Lstray 1 ESR [5-3] [5-4] Mor M. Peretz, Switch-Mode Power Supplies Transistor turn off - parasitics Lmain Transistor on Lstray Lstray D Lmain Lstray Transistor off LD Co Vo G Lstray ESR Lstray RG LS S [5-5] Mor M. Peretz, Switch-Mode Power Supplies Transistor turn off – diode forward recovery I I t VD VPK VF t [5-6] Mor M. Peretz, Switch-Mode Power Supplies Mosfef gating RL D RL RG CGS LD G RG Vgs LS LS S Vgs V'gs 2 Depend on Q Q LS C gs RL R G Vgs (real) [5-7] Mor M. Peretz, Switch-Mode Power Supplies Flyback leakage problem VO Vin Voltage spike can develop HIGH voltage Llkg Vc - ? Cdss V-? [5-8] Mor M. Peretz, Switch-Mode Power Supplies Clamp Zener diode VO Vin D–C-R Llkg Cdss [5-9] Mor M. Peretz, Switch-Mode Power Supplies Clamp configurations Vin Vc Vin n1 Vo n2 Vin Vc 3 n1 Vo n2 [5-10] Mor M. Peretz, Switch-Mode Power Supplies Parasitic inductance and physical placement Vin L1 Vin Rc Cc Llkg C L4 L2 L3 Connection of the clamp/snubber should be directly on the element [5-11] Mor M. Peretz, Switch-Mode Power Supplies Clamp design Equivalent circuit Current waveform Assuming small ripple on the clamp capacitor (will be designed that way) V VCc Vav Ts [5-12] Mor M. Peretz, Switch-Mode Power Supplies Calculation of clamp components Vo n1 Vcc n2 LLkg I av Rc Vcc _ av I pk Cc Rc Ts I av dI p I av 4 I pk t p 2 fs dt p Vo n1 Vcc n2 LLkg [5-13] Mor M. Peretz, Switch-Mode Power Supplies Design procedure 1. Select VCc av > Vo’ I av 2. Calculate Ip av Rc 3. Select Vcc _ av I pk t p 2 fs I av 4. Select Cc T > Ts 5. Adjust values [5-14] Mor M. Peretz, Switch-Mode Power Supplies Diode turn off snubber Vo Diode on Lstray snubber Diode off CD Lstray [5-15] Mor M. Peretz, Switch-Mode Power Supplies Diode turn off snubber VD CS RS CD no snubber bad snubber Vo VO Lstray VD good snubber Cs > CD 5 CS is very l arg e VO [5-16] Mor M. Peretz, Switch-Mode Power Supplies Snubber design CS RS Required values Ipk (reverse current) Stary inductance VO CD Lstray Lstray I pk 2 2 Cs Vo V 2 2 Resistor for damping Cs Rs Ts Cs needs to discharge Use simulation to optimize the snubber [5-17] Mor M. Peretz, Switch-Mode Power Supplies Switching snubber control control VGS VGS t t VS IS VS VS dI dt IS dV dt t t Jd Jp Pswitching t t The objective: avoid overlap of current and voltage Slow the rise of either current or voltage [5-18] Mor M. Peretz, Switch-Mode Power Supplies Switch snubber Vo C dV/dT (at turn off) can be slow down by adding external snubber capacitor C Vo Turn off 6 Cdss C dV I dt C Cdss [5-19] Mor M. Peretz, Switch-Mode Power Supplies Switch snubber Problem at turn on Vo EC C CVO 2 2 Pd CVO 2 fs 2 Dissipated through the transistor Solution VO CS RS [5-20] Mor M. Peretz, Switch-Mode Power Supplies Switch snubber design VO CS RDSon RS T 1 ton Rs Cs If Rds on < Rs most energy will be lost to Rs Heat Selection of Cs Selection of Rs to ensure reset ton 4 Rs Cs Question: how VDS will look if Cs is not fully discharged? [5-21] Mor M. Peretz, Switch-Mode Power Supplies Lossless (ZVS) snubber Q1 C1 L VC 2 t Q2 delay t C2 C1 , C2 of transistor plus external VC 2 IL t VDS1 t VDS2 t 7 8 Mor M. Peretz, Switch-Mode Power Supplies [5-22] Mor M. Peretz, Switch-Mode Power Supplies [5-23] Mor M. Peretz, Switch-Mode Power Supplies [5-24]