Hi im repairing a class d amp and the Ps uses Irfz44n i got in my hands p60n05 the specs are similar but the input capacitance is 2 times more in the p60n05. If the Irfz44n uses 47 omhs what value of rgate do you sugest for p60n05 considering tha the input capacitance of the Irfz44n is 1800 pf. And the p60n05 is 3900
I Was thinkin use 33 omhs
Thank you in advance!! any help Will be apreciated
I Was thinkin use 33 omhs
Thank you in advance!! any help Will be apreciated
1) The RC needs to be the same
2) The previous stage needs to be able to drive the new RC load
But since both 1) and 2) are definitely going to be compromised, it's up to you to decide how much they can be compromised - What is the switching frequency? How much drive does the previous stage have?
2) The previous stage needs to be able to drive the new RC load
But since both 1) and 2) are definitely going to be compromised, it's up to you to decide how much they can be compromised - What is the switching frequency? How much drive does the previous stage have?
Wwenze thank you for your reply, i really do not Know the switching freq, i bougth a simple osciloscope as son as it arrives i going to measure the freq.
When you said Rc you Mean R gate? I Was thinking to leave the same resitance but im afraid i could damge the fets overheating them because they do not turn off On time.
When you said Rc you Mean R gate? I Was thinking to leave the same resitance but im afraid i could damge the fets overheating them because they do not turn off On time.
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When replacing transistors in SMPS or class D output stages (MOSFET or IGBT) there are 6 essential circuit parameters of interest:
1- Turn on delay
2- Turn on current slope
3- Conduction loss
4- Turn off delay
5- Turn off current slope
6- Body diode performance
These 6 parameters also represent the 6 stages of a half switching period.
- Current slope controls EMI interference, increasing current slopes can cause self-interference problems, destructive in some circuits, just annoying shutdowns in others.
- Turn off current slope shall be similar or higher than turn on slope for reliability.
- Too high turn on current slope can damage body diodes (150V and up only).
- Increasing turn on delay or shortening turn off delay causes more crossover distortion (class D output stages only).
- Increasing both turn on and turn off delay causes more distortion in class D, is harmless in SMPS.
- Reducing turn on delay or increasing turn off delay can cause cross-conduction problems, overheating, smoke or bang!
- Conduction loss shall be kept reasonable for the transistor package in use and mounting technique, more or less dissipation can be OK.
- In circuits with current limiting based in sensing voltage drop across the power transistor only replacement with similar conduction loss type is possible without circuit modifications.
- Too much change in transistor output capacitance (d-s or c-e) can result in loss of tuning of RC or RLC snubbers used to damp switching node RF oscillations. If output capacitance is changed by more than +/-50% the snubbers in some class D output stages are likely to become det-uned.
These can be considered the guidelines for adjusting new gate resistor, and maybe other components.
- For calculating turn on/off delays: gate drive voltage, off/on state capacitance, resistance and Vgs-th at high low/high current have to be considered.
- For calculating current slopes: gate drive voltage, off/on state capacitance, resistance, Vgs/Id plot (or transconductance) and circuit+package parasitic inductance have to be considered. The drop in parasitic inductance subtracts from Vgs as seen from gate driver.
1- Turn on delay
2- Turn on current slope
3- Conduction loss
4- Turn off delay
5- Turn off current slope
6- Body diode performance
These 6 parameters also represent the 6 stages of a half switching period.
- Current slope controls EMI interference, increasing current slopes can cause self-interference problems, destructive in some circuits, just annoying shutdowns in others.
- Turn off current slope shall be similar or higher than turn on slope for reliability.
- Too high turn on current slope can damage body diodes (150V and up only).
- Increasing turn on delay or shortening turn off delay causes more crossover distortion (class D output stages only).
- Increasing both turn on and turn off delay causes more distortion in class D, is harmless in SMPS.
- Reducing turn on delay or increasing turn off delay can cause cross-conduction problems, overheating, smoke or bang!
- Conduction loss shall be kept reasonable for the transistor package in use and mounting technique, more or less dissipation can be OK.
- In circuits with current limiting based in sensing voltage drop across the power transistor only replacement with similar conduction loss type is possible without circuit modifications.
- Too much change in transistor output capacitance (d-s or c-e) can result in loss of tuning of RC or RLC snubbers used to damp switching node RF oscillations. If output capacitance is changed by more than +/-50% the snubbers in some class D output stages are likely to become det-uned.
These can be considered the guidelines for adjusting new gate resistor, and maybe other components.
- For calculating turn on/off delays: gate drive voltage, off/on state capacitance, resistance and Vgs-th at high low/high current have to be considered.
- For calculating current slopes: gate drive voltage, off/on state capacitance, resistance, Vgs/Id plot (or transconductance) and circuit+package parasitic inductance have to be considered. The drop in parasitic inductance subtracts from Vgs as seen from gate driver.
- Status
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