Bedini transistor Selector

[the_mog]

Hi Guys,

I am interested in what transistors you are using on your Bedini.

Please state if its a multiturn coil / Single / Multicoil

Also if anyone has recomended specs that would be nice to know.

The reason for this is some transistors are harder (More expensive) to get than others

thanks

K-

[sucahyo]

Definitely not 2N3055 or MJ2955. Even cheaper TIP31C/TIP32C is much better. However I found KSC5027 perform best. Although still dreaming MJL21193/MJL21194. My efficiency is more than 60% on any coil I have.

[the_mog]

How about....

TIP122 = 100V 5A
MJE13005 = 400V 4A
BU 508AF = 700V 8A

What sould a person actually look for in a decent transistor?

I would also like a few MJL21194's but that a little out of my price range on a big multicoiler maybe 1 day

K-

[sucahyo]

I think the voltage only indicate how tough it is, not how good it is at switching. Higher amp is good, but in my experience I never reach more than 2 amp current at the transistor even with 0.6 ohm coil.

The signal fall time maybe better for selecting which, but not all spec has them.

[Sephiroth]

the key to a fast switching transistor in bedini's systems is a narrow transient between the saturated mode and linear active mode. This is the mechanism that turns the transistor off, and the smaller that transient, the faster and more efficiently it will switch. Though don't know what to look for on the data sheet for that. If anyone else knows, advice would be appreciated

It would need to be rated at least 90v to have any chance of surviving the spikes (and that is if you're using a neon!). The current rating will depend on what you want to use it for but needs to be at least 5 times higher than the amount of (rms) current you intend to use.

also good linear gain is a nice quality that makes it much easier to tune. Higher gain is also desirable.

I think ST's 2N3055 is under rated... it is a cheap transistor, but for its price I think it performs very well.

My transistor of choice is the MJL21194 since it has good history. A very robust transistor that can handle huge amounts of power.

On the MG3 I am using 24 x MPSA06 transistors which I don't recommend... very fragile and the gain isn't very linear. The spec of the 2N5551 looks better, but will have to try them out before I will know how well they'll work. These two transistors are only suitable in very low power operations!

[nvisser]

John Bedini told us to use the Safe Operating Area Curve To determine your transistor.
For instance on the MJE13009, you should not go above 40V as you check what the transistor can handle safely at dc operation at 1Amp.
For the MJL21194 it is about 120V. That is why he recomends them as they can handle that high spikes
See atached curves.

[nvisser]

the key to a fast switching transistor in bedini's systems is a narrow transient between the saturated mode and linear active mode. This is the mechanism that turns the transistor off, and the smaller that transient, the faster and more efficiently it will switch. Though don't know what to look for on the data sheet for that. If anyone else knows, advice would be appreciated

]

Is it not the rise time and fall time. It is not always shown on bipolar transistors and is normally in the region of 3usec. For mosfets it is much faster like 50nsecs.
It is the time the pulse take to reach its max amplitude and vice versa.

[sucahyo]

It would need to be rated at least 90v to have any chance of surviving the spikes (and that is if you're using a neon!).

Since the spike are fast, even TIP31C with 100V rating can withstand output voltage of 200V, as long as you don't spark the output. Mine dies if I spark it (when connecting to charged battery while running).

[kdas]

Bd243c

What about BD243C? 100V x 6A x 3Mhz x 65W.

I know one guy who bedinis them with solid state device.

Regards.

[Sephiroth]

Is it not the rise time and fall time. It is not always shown on bipolar transistors and is normally in the region of 3usec. For mosfets it is much faster like 50nsecs.
It is the time the pulse take to reach its max amplitude and vice versa.

it may be, but as I understand the rise time relates to how fast the linear active region changes with changing base current, and while the transistor is operating in the linear active region.

though the base current in a bedini oscillator is suprisingly stable.

ideally, I'd want to see a graph which plots a line with constant base current, and rising c/e current on the x axis and rising c/e voltage on the Y axis... on a graph like this I would want to see a flat and very low plot (about 0.7v) with a sudden very sharp rise in c/e voltage at the end.

I haven't looked at that many transistor datasheets, so maybe this information is provided with some of them?

[SeaMonkey]

Enhanced Transistor Switching

Here's a diagram from an Application Note for a simple circuit enhancement to speed up transistor turn-off.

It's possible to easily adapt the same principle to NPN circuits as well - by reversing the polarities of the semiconductors.

When Base Drive ceases, the circuit removes 'base charge' quickly from the switching transistor which expedites its turn-off and greatly enhances the efficiency of the switch.

This technique may be used in any circuit where a switching transistor is utilized in order to improve its ability to turn-off rapidly.

[sucahyo]

Here's a diagram from an Application Note for a simple circuit enhancement to speed up transistor turn-off.

Look complicated. Where should we put the Bedini coil?

[torpex]

Hi all
My Tests:
Same circuit, same coil, only change the transistor. Measured output pulses (22 uF capacitor + dmm DCV)
2n3055 48v
Tip3055 160v
BU908 260v

The BU-508 also tried it, do not remember exactly, but I think close to BU-908.

Regards

[tecknomancer]

All that and a bag of chips

I use surplus SC5101 NPN rated at 160V 12A it's NTE replacement is NTE36 but the SC5101 I got for a Song 200 for $100.00 and when I get done blowing holes in them I can switch to NTE36 but at $5.00 I will have to be more restrained

also just in case someone needs this
Cross Reference Search

Live dangerously through surplus


VMG project has 6 Quad coils and 24 sc5101 NPN

[Sephiroth]

Here's a diagram from an Application Note for a simple circuit enhancement to speed up transistor turn-off.

It's possible to easily adapt the same principle to NPN circuits as well - by reversing the polarities of the semiconductors.

When Base Drive ceases, the circuit removes 'base charge' quickly from the switching transistor which expedites its turn-off and greatly enhances the efficiency of the switch.

This technique may be used in any circuit where a switching transistor is utilized in order to improve its ability to turn-off rapidly.

I think bedini's circuits do that any way, since once the field begins to collapse it reverse biases the b/e junction which forces it off.