Puzzling Pulse Transformer output 1

[swb1]

Hi,

I am pulsing a 1:1 pulse transformer with a 600 ns pulse and when I send 3 consecutive '1' the pulses on the output satrt to get smaller (about 350 ns). If I send 2 consecutive '1' the pulses on the output are fine. I tried putting a 1N4001 diode across the primary and secondary sides of the transformer and it didn't help. Can anyone offer any help??

Thanks,

swb1

 

[MacGyverS2000]

As with all non-ideal components, you have an inductance, a capacitance, and a resistance (impedance). Throw all of that into the mix and you have a couple of poles to deal with once you hit the correct frequencies.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[xfmrman]

I belive the transformer you are using has an ungapped core, so each time you pulse it you increase the gauss level until it reaches saturation. To use a single ended(unipolar) pulse as an input to a transformer the transformer core must have a gap to prevent saturation or a very long off-time for the core charge to bleed off.

 

[swb1]

xfmrman, the pulse pulsing the transformer is 600ns wide and happens every 3.3 microseconds. That seems like enough time for the core charge to bleed off. Am I wrong??

swb1

 

[cbarn24050]

Hi swb1, yes you could be wrong. Suppose your pulse is 5v that gives you a volt time product of 600 x 5= 3000nSV during the on time. If you have a reverse recovery diode accross the transformer the time volt product is 0.6 x 2700 = 1620nSV during the off time. Under these conditions your core "charges up" with each pulse untill it saturates.

 

[swb1]

cbarn, so are you saying that the "on-time" should be equal to or less than the "off-time"??

thanks,

swb1

 

[cbarn24050]

Hi swb1, no i didnt say that. The volt time product of the on time has to be less than the volt time product of the off time. in the worked example above it isn't and so the core would saturate.

 

[LionelHutz]

cbarn is saying to not just use a reverse diode across the transformer but some type of circuit with a larger voltage drop. In lower speed applications we have used a diode and zener in series. You could do the same but they obviously have to be high speed components and I don't know what's available off-hand.

When you pulse the transformer you create a magnetic field which is basically storing some of the enery (charge the inductor). To get rid of the stored magnetic energy you have to "move" it somewhere else (discharge the inductor). Using a snubber circuit with a decent voltage drop will quickly change this energy into heat. Our zener/diode circuit has a little more voltage drop than the DC pulse does to allow a 50% duty cycle.

I hope that makes sense.