Drive a 12 Ohm, 50mH Transformer Coil with 12V @ 1A

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Discussion Overview

The discussion revolves around driving a transformer primary coil with a signal generator, specifically using a 12 Ohm, 50mH coil with a 12V input at 1A. Participants explore circuit options, component specifications, and the implications of using different driving methods and components.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the possibility of purchasing a circuit to drive the coil or if a custom circuit is necessary, seeking the correct terminology for such a circuit.
  • Another suggests using a power FET instead of a 2N3055 and recommends searching for coil driver images for inspiration.
  • Clarification is sought regarding the voltage range of the square wave signal from the generator, specifically whether it goes from 0V to +12V or from -6V to +6V.
  • It is confirmed that the signal is indeed from 0V to +12V, and the transformer is a step-up type with a 1:5 turns ratio and a small air gap in the core.
  • Concerns are raised about whether a 5V signal from the signal generator can effectively drive the 2N3055 transistor, with one participant expressing uncertainty due to a lack of recent experience in electronics.
  • Specifications for the MJE3055 transistor are discussed, noting its power rating and the need for a heatsink when operating at 1A, along with the importance of sufficient base current for proper operation.
  • Suggestions are made to consider a two-stage circuit, a Darlington configuration, or a MOSFET if the function generator cannot provide adequate drive current.
  • One participant asks about the rise and fall times of the signal and whether adding a buffer like a 4050 would improve these times.
  • It is noted that the turn-on/off time may not significantly affect the operation due to the nature of switching an inductor, but a small capacitor across the resistor could speed up transistor switching.
  • Discussion includes the possibility of using a power MOSFET and a dedicated driver for better performance, with references to other threads for potential solutions.
  • Finally, the secondary of the transformer is connected to a capacitor and a resistive load of about 300 ohms.

Areas of Agreement / Disagreement

Participants express varying opinions on the best approach to drive the transformer coil, with no clear consensus on the optimal components or configurations. Multiple competing views on the effectiveness of different transistors and driving methods remain unresolved.

Contextual Notes

Participants discuss various assumptions regarding component specifications, driving capabilities, and circuit designs without reaching definitive conclusions. The discussion reflects a range of technical considerations and uncertainties related to the application.

Who May Find This Useful

Individuals interested in electronics, particularly those working with transformers, signal generators, and circuit design, may find this discussion relevant.

BHY-BK
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I have a signal generator that is used to generate 12kHz square waves. I want to use my signal generator to drive a transformer primary coil. My coil has 12 ohms resistance, 50mH, and will have 12V applied to it @ 1A.

Can I buy a circuit to drive the coil from the signal generator pulse or do I have to make one?
What is the correct terminology for such a circuit?
 
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Do this:
levitatorcoildriver.gif

You can get fancy to drive it with faster edges, or use a power fet instead of a 2n3055, or do a search on coil driver and look at the images for one you like
 
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BHY-BK said:
I have a signal generator that is used to generate 12kHz square waves. I want to use my signal generator to drive a transformer primary coil. My coil has 12 ohms resistance, 50mH, and will have 12V applied to it @ 1A.
12 V square wave ? Does it go from 0V to +12V or from -6 to +6 ?
What's the part number of your transformer ? Does it have a small air gap in the core ?
 
Sorry, it's 0V to +12V, transformer is one a friend made for me, it has a small gap in the core but it's not a flyback. It's a step up transformer with a 1:5 turns ratio.
 
meBigGuy said:
Do this:
levitatorcoildriver.gif

You can get fancy to drive it with faster edges, or use a power fet instead of a 2n3055, or do a search on coil driver and look at the images for one you like
Will my 5V signal from my signal generator be able to drive the 2N3055?
Dumb question I know, it's just been a while since I played around with electronics and I've forgotten a lot.
 
Probably. Do you have a model number?
Looking at the specs for an MJE3055 in a TO-220 package, it is rated for 0.6W without a heatsink. That's borderline for 1 amp. I'd use the to-220 and add a small heatsink.
Like this http://www.mouser.com/ProductDetail/Aavid-Thermalloy/6237BG/?qs=sGAEpiMZZMttgyDkZ5WiuqcEpFN0QqoQfmtMCSJ6UoA%3d

For 1A, you probably want at least 100ma base current which would be at around 4volts with a 300 ohm resistor. Can your function generator drive 100ma? If it has a 50 ohm output, then no problem.

If there is not enough drive you can go to a 2 stage circuit, or a darlington, or a mosfet. Regardless, a TO-220 package with a clip-on heatsink will be the most robust solution.

Don't forget the diode --- the transistor will blow without it.
 
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meBigGuy said:
Probably. Do you have a model number?
Looking at the specs for an MJE3055 in a TO-220 package, it is rated for 0.6W without a heatsink. That's borderline for 1 amp. I'd use the to-220 and add a small heatsink.
Like this http://www.mouser.com/ProductDetail/Aavid-Thermalloy/6237BG/?qs=sGAEpiMZZMttgyDkZ5WiuqcEpFN0QqoQfmtMCSJ6UoA%3d

For 1A, you probably want at least 100ma base current which would be at around 4volts with a 300 ohm resistor. Can your function generator drive 100ma? If it has a 50 ohm output, then no problem.

If there is not enough drive you can go to a 2 stage circuit, or a darlington, or a mosfet. Regardless, a TO-220 package with a clip-on heatsink will be the most robust solution.

Don't forget the diode --- the transistor will blow without it.
Cool, thanks for the suggestions, I'll use them. The function generator is 50 ohms! Any idea how fast the rise and fall time will be?
Would adding a buffer like a 4050 reduce the rise and fall time?
 
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Again, it depends on your generators output. Since you are switching an inductor, the turn-on/off time may not have much effect overall. You can speed up the transistor switching with a very small cap across the 300 ohm, but again, it won't change much. If the 4050 is faster than your generator, then that will help.

If speed is really an issue, then there may be better solutions than the 3055, like a power mosfet and a hefty mosfet driver (mosfets have huge gate capacitance)
There is probably some power mosfet you can connect directly to the generator and drive it without a heatsink or a series resistor.

I found some mosfets in this thread. Maybe that's a better way to go.
https://www.physicsforums.com/threads/electromagnet-and-mosfets.831892/#post-5224970
 
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What's connected to the secondary of this transformer ?
 
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Connected to the secondary of the transformer is capacitor and resistive load of about 300 ohms
 

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