Transistor Discussion

[gyulasun]

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But one last question, for all, which is the best device to use to drive a torid with a bit of current?
Should I use a MOSFET, NPN Transistor (2N3055) or a IGBT
I have a supply of transisters that drive the stepper motors out of Fisher and Paekel washing machines, these are found secured to the side of the water cooling heatsinks. Would these do? I just discovered that F&P have altered their heatsink design, no more water cooling, they are using G4RC10s transisters, hmmmmm.
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Hi Jim,

If only I knew what you mean on a torid...  Is it a mains toroid transformer or only a ferrite toroid core with some heavier wires?
Also, the frequency involved is also of importance.  And your bit of current means 1 - 2 Ampers?

The G4RC10S transistor is an IGBT, see this data sheet if it makes sense:
http://www.irf.com/product-info/datasheets/data/irg4rc10s.pdf

The earlier transistors on the bigger heat sinks are probably also IGBTs or maybe power MOSFETs, if you write down their names (type numbers stamped on their casings), we may also find some data sheets on them.

rgds, Gyula

[electricme]

Hi Gyula,
I carn't remember, its 11.30pm night, an I need a bit of sleep lol, but I will try n think.
I am using a big torid, and also smaller ones which I have taken out of PC power supplies, they are yellow ones.

I havent got a clue about the frequencies that torids work best with.
If I could get 1 or 2 amps out of them, whacko, that would be great.

Its too late to go and look at the IGBT sheet, thats for tomorrow 1st thing.
I will also post the other transister numbers as well tomorrow.

Update on my JT project, I just wound 20 turns bifilar on each torid, they work OK.
Tomorrow I have to put 480 turns on each as the secondaries.
I want to have at least 8 torids, being energised by a single JT, which powers a 4017 IC, driven by a 555, modify the markspace ratio by using pots, then when the 9th LED on the 4017 lights, it sends a hi to another set of bc548's to dump the caps energy back into the 1.5v battery. Then the 10th LED hi I will rerout back to the reset pin on the 4017 IC so it will go and do its thing all over and over again.

see if I can get a bit of OU this way.

Gyula, thanks for the reply and your help so far.
Regards
General Jim

[electricme]

@ Gyula,
I just pulled apart a different F&P motor controller, it has a number of different transistors , 6 in fact, the IRF840 I think are the ones that drive the stater coils.

The others I will take a look for myself.

Thanks for your help and I will concentrate back on the JT forum.

Hooroo
General Jim

[jadaro2600]

I've read this thread back and forth a few times now:  Is it as a result of a path of lesser resistance that the LED in the joule thief lights up?

[gyulasun]

@General Jim

Here is a link to the IRF840,  it is a power MOSFET with max 500V drain voltage and 8A drain current.
http://media.digikey.com/PDF/Data%20Sheets/ST%20Microelectronics%20PDFS/IRF840.pdf

Now I know what you meant by a torid...      

Your earlier question was: 
But one last question, for all, which is the best device to use to drive a torid with a bit of current?   

It mainly depends on what circumstances you wish to use them,  regarding their supply voltage and their collector or drain current.  Because the devices' saturation voltage'  V_CEsat given in their data sheets depend on these two data.  Of course there are devices that are especially manufactured for just high speed switching with lower saturation voltages than other types for general purpose applications.
You can see a 2N3055 transistor collector-emitter saturation voltage in Fig. 4 and 5 (page 3) of its data sheet here http://www.qsl.net/on7pc/datasheet/transistors/2N3055.pdf    You see the 2N3055 has a maximum of  0.1V  saturation voltage from  0.1A to 1A collector current when you drive the base always with 1/10 of the actual collector current (I_C/I_B=10),  from Fig. 5 ON voltages on the left.  But in case of a 4A collector current @400mA base current, the V_CEsat increases to about 1.1V, this data is not from the Figures but from the tables ON characteristics, page 2.
In case of you IGBT device, G4RC10S,  the saturation voltage is 1.1V at 2A collector current and 15V gate-emitter control voltage, data sheet does not give data on saturation voltage when collector current is lower.

So in case you have a battery (or supply) voltage in the order of 1-2V only it is obvious to choose a device with the lowest V_CEsat value because in that case the dissipation hence the loss on the device is at a minimal value too.  Say you have a 1.2V battery and you wish to switch about 100mA current via a device through you coil, than the useful voltage available will be (1.2V - V_CEsat) for induction (here I did not consider the DC and AC losses of the coil).   And if your device has ,say,  0.4V saturation voltage @100mA current, then it dissipates more than a device with 0.1V or even less saturation voltage, so efficiency suffers much in the first case.
Of course in case of  higher supply voltages like 12V or 24V or higher, the saturation voltage become negligible compared to the supply voltage hence efficiency does not suffer so much from just this. 

All in all,  the 2N3055 is still a good choice both economically and saturation voltage points of view for you toroid driver.   The IFR840 is even better, but it needs at least a 10V Gate-Source control voltage to bring its drain-source ON resistance under 1 Ohm (from its data sheet in the above link),  in which case its dissipation would be just governed by its drain current (say the drain current is 100mA, then the voltage drop across the drain-source path would be under  0.1V , this would be its "saturation voltage").

Hopefully I shed some more light on your question...

Regards, Gyula