Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Apologies, as I mentioned in #22 I have gone off topic now. I'm experimenting with a single transistor pulsing my coil. There is no capacitor because I use the natural resonant freq. found by trial and error. Then by increasing the current I want to determine if I can achieve sufficient coupling...
I'm hitting the coil with DC current pulses in one direction only so the diode is always reverse biased in normal operation. The diode protects against back EMF when the flux collapses at switch off. In this case the voltage spikes can be high and of reverse polarity to my pulses. The diode...
Actually at the moment I'm using positive only square wave pulses so a diode across the coil does not short my oscillator. I can see it does stop the large over voltage spikes caused by coil ringing.
I'm a bit confused because my TIP120 Darlington transistors have internal diode from collector...
I have the diode connected from the collector of the transistor to ground. i.e between collector (+Ve diode end) and emitter. My inductor is between collector and +Vcc rail in a basic common emitter config. I have seen this called a 'flywheel diode'.
Thanks. I've ordered a job lot of Darlington transistors to play with. (TIP 120) they were cheap and I want to try one as I read they are often used for switching. With the high beta value and 5A collector current, they seem ideal to be driven from my simple circuit. They won't be good for...
I propose adding a diode to protect against coil back emf. See link for diagram. I/P Signal source is 0-12V peak square wave at ~ 150KHz. L1 is hand made large coil unknown value. D1 TBD.
**broken link removed**
Thanks for the info. Brad. Half a million volts! I guess that is theoretical of course. At the moment I am using a single transistor in cutoff / saturation to switch my square wave and supply ~ 1A through my coil. I've had to put a 10 Ohm resistor high wattage in series with the coil to limit...
Ok yes I realise Brad has chosen L & C values in #7 to give the resonant frequency of ~ 440 KHz I wanted, but in my application I am using a large copper coil of unknown inductance and capacitance that I made as my primary. The secondary is a commercial small coil (taken from a cheap wireless...
To minimise harmonics, a sine wave at the bridge legs would be preferable and your post #8 suggested that series resonant topology would achieve this? That attracted me to this idea, but I presume there are other factors to consider that I don't yet understand?
- - - Updated - - -
Thank you...
Thank you all for the informative replies. Special thanks to Brad for drawing my attention to H-bridge with cct diagram, I had not come across that design and it does seem suited for what I want so I think I will proceed with this idea now.
- - - Updated - - -
That is very interesting, I'd...
Thanks for the advice Brian. I think I will try a 555 timer which should run astable up to 2 MHz so I will look at a standard circuit and get my square wave running. I have a signal generator so I presume I could play with a MOSFET device and feed it a square wave and see how it behaves with my...
Thanks for the advice Brian. I think I will try a 555 timer circuit to generate a square wave. I believe they can run astable up to 2 MHz so 440KHz should be fine. Then I will add the MOSFET device and see how it goes. Harmonics may well be a problem so I will measure the spectrum and if they...
My first post! ..and my first electronic project since the 1980s!
I want to design an oscillator running at 440 Khz to experiment with an inductive coupling circuit I have. Basically I have a small coil that resonates at 440 Khz and I want to drive a much larger coil with this frequency to see...
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
