Author Topic: Flyback diode for motor brushless  (Read 4346 times)

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Offline rakeshm55Topic starter

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Flyback diode for motor brushless
« on: March 22, 2017, 04:41:23 pm »
Hi..
I have a fan cntrl design where in I need to place a flyback diode across a 48V brushless type fan 19W .... I want to use smd type diode....i already have Schottky key type diode 40V max reverse voltage in stock....Can I place 2 of such diode in series as flyback (40+40)???...Will such design be sturdy ??. Or do I need to choose diode with higher reverse voltage.....I was trying to avoid procurement of new parts .....pls advice
 

Offline james_s

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Re: Flyback diode for motor brushless
« Reply #1 on: March 22, 2017, 04:54:55 pm »
Is this for a one-off hobby project or a commercial design?

Generally you can get away with putting two matched diodes in series. It isn't always a good idea but it will probably be fine.
 

Offline rakeshm55Topic starter

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Re: Flyback diode for motor brushless
« Reply #2 on: March 22, 2017, 05:42:13 pm »
This is for an industrial design....Since I was already using a similar part in other section of design I thought of using the same diode......If putting them in series is not a recommended practice then I would use an appropriate part......
 

Offline Zero999

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Re: Flyback diode for motor brushless
« Reply #3 on: March 22, 2017, 05:42:13 pm »
The usual reason for doing this is to increase the reverse blocking voltage but it doubles the forward voltage and it can be problematic ensuring the reverse voltage is shared between each diode. In this case it's not a good idea and is completely unnecessary, as silicon and Schottky diodes with a higher reverse blocking voltage than 48V are widely available and aren't expensive.

If this is just a quick prototype and you're on a tight timescale. Order the correct components, then use two 40V diodes in series, just to get it working, whilst you're waiting for your order and replace them with the correct diodes, as soon as they arrive.
 

Offline MagicSmoker

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Re: Flyback diode for motor brushless
« Reply #4 on: March 22, 2017, 08:29:00 pm »
Wait just a second here... why do you need a flyback diode for a brushless fan? Brushless fans are essentially tiny AC motors with an integrated inverter, so you don't need an external flyback diode because they are already present across each switch in the inverter.

edit: grammar
« Last Edit: March 22, 2017, 10:58:01 pm by MagicSmoker »
 

Offline james_s

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Re: Flyback diode for motor brushless
« Reply #5 on: March 22, 2017, 09:44:13 pm »
That's a good point. I had assumed the OP was designing an inverter to drive a brushless fan motor rather than a self contained brushless fan but now that I read it again I'm not sure.
 
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Offline rakeshm55Topic starter

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Re: Flyback diode for motor brushless
« Reply #6 on: March 23, 2017, 03:43:31 am »

Great!! Thank you for your suggestion .... So I may not need flyback protection for a brushless fan ..... i am attaching my choice of fan and pwm controller IC

Fan spec
http://www.ebmpapst.com/en/products/product_search/productdetailaxialcompact.php?pID=53812
PWM controller
http://ww1.microchip.com/downloads/en/DeviceDoc/21755C.pdf

 


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