Actually, the diode is there to repvent *damage* not to improve results, which it won't.
So, there's 6V across the 2N3055 too ?
There is clearly something fundamentally wrong here. it wil be something to do with how you've connected things.
I suggest you post a schematic in a suitable place ( not here since this isn't a binaries group ).
Graham
I tried the buz21 mosfet , it work good, but heats up real quickly. thats a reason why I wanted to use the 3055. . The buz21 only work when I apply at least 5v to the base. Itried a new 3055 with only 1v at the base as Jamies suggested, but it did not work. I really want to get it going with the 3055 transistor
k
Buz21 spec is 100 volts and point one ohm on resistance. It shouldn't be getting hot. Same application? source to ground - drain connected to the coil and coil connected to positive?
If that got hot, something is wrong. Possibly it needed more gate voltage - I don't have the specs in front of me - as a rule of thumb I figure an N channel mosfet should turn on with about +4 volts on the gate- and that is close to its linear region (not turned on fully)
All Mosfets require a fairly high gate voltage to turn on (that is an intrinsic characteristic of the part) - but a very low gate current (Pico amperes - compare that to the 3.3 amps a 3055 wants to switch ten amps.)
Another thing you can encounter with a mosfet is the gate drive current is so low that a sloppy layout can pick up stray power line hum, or an on board ground loop causing oscillations, or some dirt that is conductive - get one of them toggling at a mega hertz or so and they do get warm.
The only time they become hard to drive is when you try switching them fast - then the relatively high gate capacitance will take some current . In a low frequency or DC application that doesn't apply. High frequency to a power mosfet would be ~20 kHz or higher - In that case the power goes to charging and discharging the gate capacitance rapidly - reactive current, does no work, produces no heat, but you still have to be able to supply it..
A 2N3055 with a volt of positive polarity on the base with respect to the emitter (emitter grounded) should be turned on very hard. Most bipolar transistors turn on at point six volts and are over driven at .7 volts. One volt base drive is a lot. At that current the collector should be very close to ground potential.
It should be working . . . Bad batch of parts, wrong part entirely, bad or just destroyed part? (they can't have an unlimited current pumped into the base - over seven amps will destroy them) You must be overlooking something.
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if you are truly applying 4 volts to the base with the Emitter to common then you have already damaged your 2N3055. you should be reading around 0.5 ... 1.0 max on that base . is it possible you do not have your battery ground connected to the 555 common ? if so, if your worried about isolation then use an opto-coupler.
-- Real Programmers Do things like this. http://webpages.charter.net/jamie_5
After some more testing, the BUZ21 do not heat,.. thats good. I ordered ten 2N3055 from digikey. They cant be all scrap... could they? I will do some more test on them tonight or tomorrow. I worked on this all day. I used 0.5 volt to the base of the 3055, but I maybe there is not enough current to drive it. My ammeter cant detect anything. from the specs: http://www.ortodoxism.ro/datasheets/motorola/2N3055.pdf Ib max is 7amps and Veb is 7v so emitter is grounded leaving a max of 7v to base. I'll work on this a bit later or maybe choose another high power transistor.
ken
if bipolar it does, the cmos ones can't source much.
They can sink a reasonable amount though.
-- Bye. Jasen
Just to be on safe side, when you say: from the collector to emitter. you mean positive on the collector ? I only have 0.1uF left 35 and 50 v ones.. I assume electrolytics? I just want to make sure I do exactly hat yuou want me too. My ideas bank is practically exhausted. I hope to wake up with some new one tomorrow :)
ken
Your parts should be good. Digikey is a prime source and unlikely to be trash.
The base emitter junction takes .6 volts to turn on .5 probably won't turn it on at all. It is a diode junction - begins to conduct at point 6. A hot transistor will conduct with a lower base voltage. Heat it to 100 C and it would probably switch on at .5 volts.
The 7 volts you're quoting is the absolute maximum rating - that's the point where it smokes - not part of anything you're likely to see (except maybe with a scope in a high power dynamic application - like a brief spike)
Look down at the "on" voltages graph that's where you should be running and with a 50 ohm coil (if that's right) you should be working with about point 65 volts.
2N3772 or 2N3773 are somewhat better parts and frequently used to replace the 3055. But if the 2N3055 isn't working it is unlikely another bipolar will.In one of your posts you make it sound like you connected the 555 directly to the base of the transistor without a current limiting resistor - if so it is probably dead.
Test the transistor to make sure it turns on when it should:
Put your transistor emitter to ground, collector to the coil and coil to +12. Nothing should happen. Connect a 100 ohm resistor from +12 to the base and the coil should turn on - that tests that part of it.
Connect the 100 ohm to the output of the 555 (pin 3) and it should turn on and off with the oscillator.
It wouldn't be a bad idea to put a damping diode across the coil (a reversed biased diode across the coil (band lead, cathode to +). Then when the transistor switches off the voltage spike won't eat the transistor.
I have an induction coil that easily produced 450 volts when it switches off from a 20 volt power supply. I use a horizontal drive transistor (actually three of them in parallel) rated for 450 volts and it still requires a zener to protect the transistor (can't use a damping diode in this case because I want it to "ring" when it switches - that 450 V spike produces 100,000 volts on the secondary)
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you better put a diode test on the base to emitter of those transistors to make sure they are still alive. in any case.., you don't apply that much current in the base.
try a 60 ohm or near it from the 555 output driving the base. place a cap of lets say around .01 from the collector to emitter.
-- Real Programmers Do things like this. http://webpages.charter.net/jamie_5
Yes, that's normal. It would work better still ( less heat ) if you applied more volts to the gate.
Bipolar transistors are not *voltage driven* they are current driven.
Your immediate problem seems to be a lack of understanding of basic electronics.
Graham
huh??? should be half as strong.
Bye. Jasen
yes, and to create current I have to add a resistor in the output of the
555, I tried 5kohm ( little current) and 10ohm (lots of current) but nothing.Ken
No, it doesn't 'create' current. That's to *limit* current so the 555 isn't driving a near short circuit ( the 2N3055's base ) , or more accurately - to define the base current.
Well you're clearly doing something basic very wrong.
I note you haven't posted a schematic yet.
Graham
You're right - ampere turns, cut the current in half with the same current and the ampere turns is 1/2 not 1/4 as I stated.
Ken is getting me confused.
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Good observation. I've been taking it for granted he's using a standard NE555. If he was using a cmos part and trying to drive a workhorse like the 2N3055 that would explain some of the problems.
The other thing I tend to doubt is that the coil has a resistance of 50 ohms.
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you are right, I made a smallpage for this effect:
the resistance of the coil is 10.2 Ohms I am using the chip NE555N from
I am getting a good effect with the Buz21 chip (mosfet). I just want to do it with the 2n3055.
ken
I can believe the ten ohms. I rewound the rotor for my motorcycle and it was 4 ohms and, surprisingly, uses a 3055 for a regulator.
Ten ohms shouldn't take a lot of base drive it is only just over an amp.
What is that thingee between what appears to be the base and emitter of the 3055 - a diode? How is it in the circuit - forward or reverse biased? can't see the cathode band . . . that has to be reverse biased to allow the 3055 to have enough current to work - and it is totally unnecessary no matter which direction it is in - might be of some use with a mosfet to protect the gate, but not with a bipolar.
Air core coil? Iron has 800+ times the permeability of air, so an air core electromagnet is weak indeed.
There's nothing to be gained from using two power supplies - one for the 555 and one for the load coil. The 555 is happy working from 12 volts and will provide some more base drive to the 3055.
And that may account for the heating in the mosfet you saw earlier (two batteries). 6 volts is too close to the 4-5 volts the mosfet needs to turn on completely. The 555 can drop a volt or two and that puts the mosfet in its linear region (not turned on fully - drops voltage across it - generates heat)
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Well it was originally remove, as in none, Someone told me to trythat but i left if for the picture. It has been removed.
No there is iron in there, there is duct tale over it because there are small rods
would the batteries affect from working or not? I will try it.
I will also put a voltage divider to i get about 0.5 volt into the base as I did before. (Not in the picture)
ken
Oh. OK sounds like my induction coil. Lots of small wires.
Just run the 555 from the 12 volt supply
What is this about a voltage divider? The 555 outputs a source (connection to the + supply - internal to the 555). You put a current limiting resistor to keep the 555 from dying in an effort to supply the (effective short) base emitter junction.
A "voltage divider" implies, to me, that you put two or three resistors to set the base voltage - that isn't how it is done=== the
555 can output just so much current. The 3055 will eat that current and more (killing the 555 if you don't limit it)The way it is normally done - you calculate the current that the 3055 needs to turn on with the load you have. (from the data sheet on the
3055) That will be about 100 milliamps with a 10 ohm coil working from a 12 volt supply. The 555 can source over 100 milliamps (source=puts out a positive voltage and current, "sink" is the opposite - takes the current to ground). 555's do both - sink and/or source.That's plenty to turn on the 3055. You figure your power supply voltage, the drop inherent to the 555, the drop inherent to the 3055 (the six tenths of a volt or so) and calculate a current limiting resistor so that the 3055 turns on and the 555 doesn't die.
The short answer: There should be a 100 or 200 ohm resistor between the 555 and transistor base. It should be capable of dissipating a watt of power - not the 1/4 watt resistor we all work with - bigger.
There should be no diode between the base and emitter.
There should be a reverse biased diode (cathode (side opposite the arrow) or the band on the diode) to the plus 12 V and coil where it connects to the 3055 (that will keep the 3055 from shorting when it tries to interrupt the current and creates a big voltage spike. - the diode is reversed biased so doesn't eat any current. When the transistor switches off it absorbs the reverse EMF and saves the transistor from the high voltage spike.
(common practice with coils driven by transistors)
Can you watch the alt.binaries.schematics.electronics Usenet group? I can draw and post a jpg to show it.
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Hi I did as you told, put everything on the 12v battery. butmy 555 did not like that, one reason why i was putting it on 6v. It blew up in flames.. do they put gun powder in these thing? I,ll have to wait and buy some more tomorrow.
ken
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