Author Topic: QWERTY  (Read 11912 times)

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Offline pranavTopic starter

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QWERTY
« on: April 30, 2017, 04:01:27 am »
...
« Last Edit: June 27, 2022, 03:24:08 am by pranav »
 

Offline ataradov

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #1 on: April 30, 2017, 04:48:30 am »
It looks like OP is asking how to apply diodes to the flyback transformer. If it is the case, then you need to clarify what you are doing exactly.
Alex
 

Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #2 on: April 30, 2017, 04:53:31 am »
It looks like OP is asking how to apply diodes to the flyback transformer. If it is the case, then you need to clarify what you are doing exactly.
This is schematic of circuit of my single transistor flyback driver

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Offline ataradov

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #3 on: April 30, 2017, 04:58:07 am »
That's a very-very simplified schematic. It is basically useful for teaching purposes only. I would not use that in anything real, especially dealing with high voltages.

But if you really want, then connect this diode across the primary winding. But your main concern here is flyback voltage. You need to design a proper conditioning circuit, and not just feed it into the base of that poor transistor.
Alex
 

Offline Seekonk

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #4 on: April 30, 2017, 11:30:20 am »
Put a diode across the primary of your cars ignition coil and see how far you get, literally. The primary of an ignition coil peaks around 300V, it has to.  You haven't listened to what was said before, you need a better transistor.
 

Offline T3sl4co1l

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #5 on: April 30, 2017, 02:17:00 pm »
I posted one picture and one link in the last thread. Did you read them?

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Online Zero999

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #6 on: April 30, 2017, 04:02:26 pm »
I've read that we can protect transistors from inductive spikes by connecting diodes across the load. How to do it exactly for this...
Another common beginner error here, seems to be making too many darn threads on the same topic. You'll find it easier, if you keep all of your questions about the same circuit/project to one thread. Before going any further, please check all of your replies to your other threads:
https://www.eevblog.com/forum/profile/?area=showposts;sa=topics;u=136909

With a flyback converter, you want the back-EMF to generate a very high voltage, which is transferred to the secondary by the turns ratio of the transformer. You may need suppression but it's no good limiting it to 0.7V as you would with a relay driver.

I didn't bother with suppression. When I made this circuit, I used a high voltage transistor which could easily handle the high voltage spikes with no trouble.
 

Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #7 on: May 09, 2017, 10:50:04 am »
I've connected a diode across the primary but now I can hear a high pitch noise from the load. Is it normal? Is it done?

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Offline danadak

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Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 

Offline oldway

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #9 on: May 09, 2017, 11:40:50 am »
Do not forget that the free wheeling diode must be a fast recovery one.  :-+
 

Online Ian.M

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #10 on: May 09, 2017, 01:54:15 pm »
For a flyback converter you *NEED* that inductive spike.  If you damp it out with an anti/parallel diode, you are limiting the dI/dt which is directly proportional to the rate of change of flux and thus the voltage induced in the secondary.

The classic diode snubber circuit for flybacks has a fast diode in series with a parallelled resistor and capacitor D-(R|C).  The resistor is chosen to discharge the capacitor sufficiently between pulses to keep the voltage below the max Vcbo of the transistor (assuming a low impedance base drive, otherwise Vceo), and the capacitor is chosen as a compromise between size/cost, minimising the voltage swin during a pulse so it can operate closer to max Vcbo, and the startup load due to the flyback having to charge the snubber cap to its intended voltage before the secondary output will reach its design value. 

For initial experimentation, replace the resistor with a series string of a much smaller resistor that will drop approx 10% of the max Vcbo if the maximum inductor current is passed through it and one or more reverse biassed Zener diodes, to make up the bulk of the snubber discharge voltage drop, of 70% of max Vcbo.  That configuration although a lot more expensive is far more forgiving if the back-EMF spike is larger than expected, or the load on the secondary is varying and once the mean discharge current has been determined, you *may* then be able to replace it with a simple D-(R|C) snubber.
 

Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #11 on: May 27, 2017, 05:12:25 am »
Will S2000N transistor will withstand the spikes?

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Online Ian.M

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #12 on: May 27, 2017, 05:42:16 am »
Will S2000N transistor will withstand the spikes?
With a 12V supply, probably, with only a minimal RC snubber to round off the spike a bit to keep it under 700V, but its a real bitch to drive - it needs >2A into the base to get the saturation voltage down to 1V, then you have to slam the base negative by a volt or so to get it to turn off quickly.

See fig1 in its datasheet.  Note the second 3TH41 diode to the right of the transistor under test (the S200N), going to a 1Meg resistor and 0.1uF cap, thats the D-(R|C) snubber network I mentioned above.
« Last Edit: May 27, 2017, 05:53:13 am by Ian.M »
 

Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #13 on: May 27, 2017, 06:56:45 am »
Will S2000N transistor will withstand the spikes?
With a 12V supply, probably, with only a minimal RC snubber to round off the spike a bit to keep it under 700V, but its a real bitch to drive - it needs >2A into the base to get the saturation voltage down to 1V, then you have to slam the base negative by a volt or so to get it to turn off quickly.

See fig1 in its datasheet.  Note the second 3TH41 diode to the right of the transistor under test (the S200N), going to a 1Meg resistor and 0.1uF cap, thats the D-(R|C) snubber network I mentioned above.
Mmm...that means I could probably drive it with a 12V 600VA battery...

With a 47 ohm series resistor b/w primary & base of transistor, is there anything else I need to do...?

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Online Ian.M

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #14 on: May 27, 2017, 07:46:28 am »
If the feedback winding has enough turns to get enough drive through the 47R resistor to get it to saturate, it willl exceed its 5V reverse Vbe limit when it cuts off. 
 

Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #15 on: June 03, 2017, 11:32:37 am »
I've used a ballast circuit and it's now working properly. Thanks to everyone..!



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Online Zero999

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #16 on: June 03, 2017, 03:52:14 pm »
You're lucky to still be alive.  :palm:
 
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Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #17 on: June 04, 2017, 10:58:29 am »
You're lucky to still be alive.  :palm:

I know the seriousness[emoji16]

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Offline Le_Bassiste

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #18 on: June 04, 2017, 11:26:31 am »
"Herr, vergib ihnen, denn sie wissen nicht, was sie tun." :-\
An assertion ending with a question mark is a brain fart.
 

Offline pranavTopic starter

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #19 on: June 05, 2017, 07:56:28 am »
I'm still alive and my experiments of lichtenberg figures:
 

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Online Zero999

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Re: How to protect transistor from inductive loads? Using diodes?
« Reply #20 on: June 05, 2017, 08:15:53 pm »
I'm still alive and my experiments of lichtenberg figures:
 

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Wow, more proof you're completely incapable of following basic safety procedure. |O
 
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