Author Topic: Opto - Transistor Pulsing Circuit  (Read 17525 times)

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Re: Opto - Transistor Pulsing Circuit
« Reply #32 on: August 24, 2010, 03:49:39 am »
is this what you meant seb? i have question marks in areas of question

(http://i82.photobucket.com/albums/j243/outlawstc/101_1016.jpg)

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Re: Opto - Transistor Pulsing Circuit
« Reply #33 on: August 24, 2010, 04:16:17 am »
Dam that schematic is wak as hell .

What are those useless diode . What  is that wasted 13mA half of the time . What is that 20 ohm resistor , it only slows down the charge and leads to more heating .  And you dont even let me know what pin 7-6 do there unless I look for myself .

Also ,a heatsink does not have to be used unless you are doing a bad switch .

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Re: Opto - Transistor Pulsing Circuit
« Reply #34 on: August 24, 2010, 08:10:42 am »
Hello
Sorry i got very little time today to do the drawing but i tried to make the best i could... Tomorow i make it more clear to you...


Yes outlawstc


The left question mark is connected to the positive side (is an electrolytic capacitor) 


and yes the unmarked pins were 6 and 7


The diode on the left is good to avoid problems with ground loops thus will protect the driver and should be about 5 amp diode if possible...


Dankie, The 20 ohm resistor is there to limit the current, and is needed as a mean of avoiding undesired resonance or oscillation, false triggering,  on the mosfet witch can lead to destruction of the driver and mosfet... (it reduces the Q factor there)  (20 ohms is the min recommended on the data sheet)


Outalwstc on thing you miss is the protection diode on the on off switch witch directs the spike from the coil to the battery when you turn off the circuit avoiding damage to the transistor...  (the parallel capacitor with the primary is also for protection and is also a mean for make the power to be used more efficiently as the coil instead of discharging back into the battery witch will not readily recharge (the case of  having an anti parallel diode in paralell with the coil) Thus the coil will discharge on the capacitor, so the energy will be there available for the next pulse ...  there are other strategies thought like adding also a resistor in parallel but keep it simple... This would be called snubber is meant for protection...


(There are other thing called the earth capacitor with is just a big capacitor connected between a small coil and the battery with a diode in series before going to the primary witch serves as this way back to the unused energy... However the parallel capacitor do the job-... )


The diode on the switch is very important because it creates a path for the current to go when the circuit get open (if this diode were not there the spikes would go to the transistor and time after time will destroy it!  (the represented switch is a three way switch and you just need to connect it just like i draw it! easy like this 


The capacitor in parallel with the drain and source is there for the same reason, when the current change direction on the coil it reverse polarity and thus allow the transistor to completely turn of... It also Reduce the spike peak protecting the transistor during the switching operation for the 
same reason as the diode on the switch...


people use to draw a diode in antiparallel, i tried practically but i found that the capacitor is way better and that it makes the transistor to work cooler... 




Is very easy circuit


For better understanding i recommend that you google the component names and there will be datasheet with some more information on the devices and there will be some schematics hopefully with the explanation for what every pin stand for....


Is never late to learn something new


Hope it help


see you tomorrow


Regards

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Re: Opto - Transistor Pulsing Circuit
« Reply #35 on: August 24, 2010, 08:45:53 am »
OHHHH


Sorry I did something wrong
 
the 1000ohm resistor should be connected from the gate to the ground... sorry for that one i have just noticed

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Re: Opto - Transistor Pulsing Circuit
« Reply #36 on: August 24, 2010, 10:10:09 am »
Look


i decided to show you another way...




The blue is the direction of the current during the on pulse


the red is ... during the off pulse...


The big diode works like a switch that only opens when the voltage of the battery is greater than the voltage on the capacitor...


The diode in parallel with the mosfet allow for the current or (non used energy) go back recharging the capacitor...


The "switchs" diode protects the mosfet as explained in the other post...


The pink diodes protects the circuit in the case the polarity of the coil reverses, aways recharging the capacitor instead of blowing out the energy... 


When the voltage in the capacitor is bigger than the battery voltage the big" diode stop conducting making of the capacitor the source of the energy at least until its voltage is grater than the battery voltage...


This capacitor should be big if possible and rated for maybe 50v, and should be an efficient one (not electrolytic would be better) (it will work as the earth ground witch i mentioned....




If you connect a diode in parallel with the coil, (like on stans papers) simply when the pulse is off all the energy you inputed on the coil will be shorted on the coil because the polarity will reverse and the diode will than start conducting... (if you want to try this way, use high power diodes cause will get really hot)


Best regards 
« Last Edit: August 24, 2010, 18:27:22 pm by sebosfato »

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Re: Opto - Transistor Pulsing Circuit
« Reply #37 on: August 24, 2010, 16:43:20 pm »
this better?
(http://i82.photobucket.com/albums/j243/outlawstc/101_1017.jpg)


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Re: Opto - Transistor Pulsing Circuit
« Reply #38 on: August 24, 2010, 18:11:25 pm »
This is the circuit i named the components so we can more easily talk about them


You could also use irf 540 witch is also a good mosfet with low rds on  (the irfp250 is better however)


C1 should be about 15uf if possible a paper capacitor (not electrolytic )
 
C2 could initially be around 200nf but you can tune the circuit for a certain frequency adding other capacitors in parallel, play with some values and look at the oscilloscope, it will depend on your load, inductance... 


C3 from 100nf to 200nf would be just fine


For the diodes you can buy some 1n4007 and use them in parallel so you can make any diode you need... If they get hot add more diodes in parallel...


the 20 ohm resistance should be 2 watts


the 1000 ohms 0,5 watts is fine






« Last Edit: August 24, 2010, 19:57:26 pm by sebosfato »

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Re: Opto - Transistor Pulsing Circuit
« Reply #39 on: August 25, 2010, 03:54:08 am »
Circuit from haithar is up and running, more details in a sec

first test, i have a comment about amp restriction and inductive reactance

~1000 Hz , 1.3 amps
~2000 Hz, 1.1 amps
~3000 Hz, 1.0 amps
~4000 Hz. 0.88 amps
~5000 Hz, 0.5 amps
~6000 Hz, 0.17 amps
~7000 Hz, 0.11 amps
~8000 Hz, 0.08 amps
~9000 Hz, 0.04 amps
~10,000 Hz, 0.02 amps
~11,000 Hz, 0.01 amps

drawn from power supply, the chokes are restricting amps!
inductive reactance = 2 pi f L