[BLDC] The mosfet gets too hot and dies. help me

Hardware
1

Hello. Nice to meet you.

fig
fig984×600 105 KB

[Specification specifications]

  1. BAT(+): 28~32VDC
  2. MCU: STM32F103C8T6(STMDuino)
  3. Circuit diagram: see picture
  4. MOSFET: IRF3710
  5. BLDC MOTOR SPEC: 400W (24VDC)

[Problem]

  1. The MOSFET receives a lot of heat.
    Should I change to another MOSFET?
    Is the 'IRF3710' MOSFET wrong?

  2. Is there anything wrong with the circuit diagram? Having trouble?

Please advise. help.

2

Post a proper schematic, complete with component values and full identification of ICs.

Show the common ground connections.

2 Likes
3

The MOSFET does not receive heat it generates it when overloaded, not driven properly, not heatsinked adequately and many more. Along with the schematic show a picture of the assemble. Also it appears this is a three phase motor so include a link to that as well. Can you post scope photos of the gate drive on one channel, both fets, and hopefully a current trace.

2 Likes
4

@jremington , @gilshultz
Thank you for answer.

fig2
fig21095×615 370 KB

  1. If a lot of current is applied, the MOSFET will die.
  • I did not check it with an oscilloscope.
  • When there is no load, 1-2A of the motor operates well.
  • If there is a load, the motor will die immediately if it is 10-15A.
  1. And, we want to change the MOSFET to ‘CSD18542KCS’. The current and resistance specifications are good, so it appears to generate less heat.

Please review.

5

Please post a complete schematic diagram. The picture of a PCB is useless.

1 Like
6

My guess is that you are getting what is called "shoot through". This happens when both the top and bottom of a pair of FETs are on at the same time for a short time during the process of turning one on and the other off.

This in effect causes a short circuit through the FETs and hence you draw a lot of current and the FETs will generate a lot of heat and so burn out.

3 Likes
7

The bootstrap caps and diodes are also suspect.
A common 10uF electrolytic smd can can't supply the several Amp gate pulses.
Probably needs to be Tantalum. See the chip's datasheet.
Same for the caps on the 12volt rail (chip).
Diodes must be fast recovery (Schottky). The diagram shows common diode symbols.

A 23 milli Ohm fet has a static dissipation of ~4.5W at 10A. Without the switching losses.
Those heatsinks can maybe dissipate 2W.
Leo..

2 Likes
8

@jremington

figss
figss2315×521 278 KB

The circuit diagram is also attached.
Please review.

9

@Grumpy_Mike, @Wawa

Thank you for answer.

  1. I will replace the Schottky diode with one with a faster response.
  2. 'A common 10uF electrolytic smd can can't supply the several Amp gate pulses.'
    Can you explain in detail what the above means?
  1. Are you saying the value is too small?
  2. Or are you saying that it is a problem because of polarity?
10

If you already have a Schottky diode there, then don't replace.
The first schematic shows a common diode. A Schottky has another symbol.

The gate of a fet is like a capacitor. For fast switching of the fets, that capacitance needs to be charged/discharged fast, which the gate driver chip tries to do.
But that energy has to come from somewhere. The supply caps. Stick with the value that the driver datasheet gives you, but use caps with a low ESR (Google that).
Leo..

2 Likes
11

@Wawa

Thank you very much for your reply.

  1. I roughly understand what you mean.

  2. It is related to Schottky diode.
    The old PCB used M7.
    I am planning to use 'SS34' as a Schottky diode.
    What do you think about this?

1 Like
12

Any Schottky >= 1Amp diode should do. SS34 is fine.
Which gate driver chip, and what value are the stopper (gate) resistors.
Leo..

1 Like
13

Thank you for answer.
[old pcb]

  1. chip: IR2104
  2. gate resistor: 100[ohm]
  3. cap: 10[uF]

[New plan]

  1. I want to change the resistance from 100[ohm] to 10[ohm].
  2. Cap: I want to change it to 2.2[uF].
  3. I want to change the MOSFET to 'CSD18542KCS'.

Could you please give me some advice?

14

10 ohm is a more realistic value. 100 ohm sort of defeats the use of a gate driver chip.
A 1N4148 smd diode on top of the 10 ohm resistor could further reduce switching losses.
Google "ir2104 circuit diagram" (images).

The type of cap is more important than it's value.

The 3.3 milliOhm of that fet is much better than 23 milliOhm.
But sort out the gate drive chip parts first.
Leo..

1 Like
15

@Wawa

Your help was very helpful.
However, there is one problem.

  1. I understand the concept of ‘ESR’.
  2. However, it is difficult to find the 'ESR' value published in the capacitor datasheet.
  1. 2.2uF
  2. Polarized products
    By any chance, can you recommend a product number? Or even the manufacturer?
    No matter how hard I search, I can't find a capacitor with 'ESR' written on it. I don't know which is better.
16

Good brands have datasheets.
You might have to use electrolytic for that voltage.
Leo..

1 Like
17

You will never find a capacitor with the ESR written on it. It is only on the data sheet you will find this. And if it is not on the data sheet then it must be a bad figure, so reject that one as well.

1 Like