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mosfet dri

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ออฟไลน์ surachit

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mosfet dri
« เมื่อ: 16,พฤศจิกายน, 2019, 07:54:51 »
There is a 9.1v zener connected from their emitter to the 0v line. This has two functions: one is to help protect the MOSFET from transient voltage spikes (usually generated by noisy motors). The second is to help protect the drivers and the rest of the circuitry in the event of a MOSFET failure. As such, it is ‘sacrificial’ and must be tested!
The low side gates are driven by 10 ohm resistors: these are also sacrificial as when MOSFETs fail, they often go through a stage where drain and gate are shorted – this feeds back current into the control circuitry. The CR16 size 10 ohm resistors usually fail open-circuit whereas larger CR25 size resistors can burn, even sometimes damaging the circuit board. CR16 resistors give significant protection – though this is not 100%!

If a MOSFET fails, always measure the gate resistor with an ohmmeter – the gate resistors can go to a high resistance which will prevent proper operation.

High Side
The PWM from the modulator also feeds Tr17: this is the high side switch. There is a capacitor present to speed up its switching so that the high side is allowed to switch on (Tr17 off) only when the low side drive is off.

The high side gate drive is via a ‘bootstrap’ pump. When the low side MOSFET turns on the 1µ0 capacitor charges up to full battery voltage via the 22R and the diode. When the low side MOSFET turns off, the motor current commutates through the hiside MOSFET which goes into conduction as a forward biased diode so its source rises to slightly more than the battery voltage. The top of the 1µ0 capacitor rises to twice the battery voltage. Since TR17 is off, current flows through the 47K switching on the complimentary emitter followers Tr12 1n3 Tr13. The hiside MOSFET switches on.

The gate drive voltage to the high side MOSFETs is limited as the base of Tr 12 and 13 is clamped by a 9v1 zener to the source of the high side MOSFET.

The terminal marked ‘Out’ feeds the motor negative – motor positive is to battery positive. Also fed from the ‘Out’ terminal are two sensing circuits: one refreshes the ignition circuity so it remains on until the controller has stopped switching. The second feeds the high side and low side current limit circuits.

Failures
When a MOSFET fails, a chain reaction can occur. There are several MOSFET failure causes and the events are fast and very difficult to properly diagnose, so it is usually difficult to guess at the causal event. So it is sensible to remove all MOSFETs from circuit and test the drive circuitry. On NCC-60 and NCC-70 you will also have to remove the main capacitor. On NCC-35, it can remain. MOSFETs can be tested out of circuit, see MOSFET testing.

Inspect the drive components associated with any failed components. Replace any visibly damaged components.

NCC   VTX
No   Value   No   Value
Tr 12   BC 337   Q 20   BC 817
Tr 13   BC 327   Q 18   BC 807
Tr 18   BC 337   Q 19   BC 817
Tr 19   BC 327   Q 17   BC 807
Other components values are marked on the circuit and type used is not critical. If replacing the drivers with other types, choose a driver type something which can handle several hundred milliamps. The circuit will work with common transistors such as BC 547 and BC 557 but this results in slightly inferior drive waveforms.

Most common failures
in some sort of order of liklihood:

Low side
MOSFETs
Gate resistors
PNP driver (BC327)
Gate clamp zener
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ออฟไลน์ surachit

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Re: mosfet dri
« ตอบกลับ #1 เมื่อ: 16,พฤศจิกายน, 2019, 08:00:36 »
face หนุ่มกิโลสี่ บุญยัง  0866209426  
[email protected]