1. Home
  2. Electronics Design
  3. series current

series current

Hi,

Figure 1 Link:

formatting link

Figure 2 Link:

formatting link

I experimented with the circuit shown in figure 1. It worked as expected. The series current is 6A peak at resonance frequency of

100KHz with 50 percent duy cycle. The voltages across the inductors L1 and L2 are 450 V peak to peak respectively.

I wanted to increase the current in the coils to get more magnetic field which I can not do with 100KHz as I maxed out on the ON time. So, I changed the frequency to 69KHz. Replaced the resonant capacitor as shown in figure 2. But this time I did not get the 10A peak current with the voltages 450V peak to peak across the inductors L3 and L4. I found that the current is still 6A peak.

I do not know the reason why the current did not increase. Any suggestions.

Thanks

jess

Reply to
Jessica Shaw
Loading thread data ...

I mistakeny put the value of the capacitor 45nF in figure 2. Its

53nF.

jess

Reply to
Jessica Shaw

The current in a series resonant circuit depends entirely on its effective series resistance. The reactive components cancel out.

What you are seeing is what I would expect to see. Neglecting small effects due to skin effect, reducing the resonant frequency, and the exciting frequency accordingly, should have no effect on the current at resonance.

I= V/(R+j(wL-1/wC)), where w = 2.pi.f If wL = 1/wC (resonance), you are just left with R.

Quite how, or why, you expected to see 10 amps, I don't know.

TANSTAAFL.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)
Reply to
Fred Abse

Same JPEG. You mean Figure 1 == top and Figure 2 == bottom, right?

Don't know if this is the entire reason, but the resonant frequency I calculated for Figure 2 (bottom) is 75 kHz. Try bumping C2 up to about 54 nF, or tweak the drive frequency and see what happens.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Entropy: When your shoelace comes untied, you can't fix it
         by walking backwards.
Reply to
Paul Hovnanian P.E.

Is this an actual circuit or a simulation? If this is a simulation with=20 ideal components, you need to add such things as series resistance and=20 breakdown voltage. If it is an actual circuit, the peak current and peak =

voltages will be limited by real parameters such as these, as well as = the=20 current and power available from the DC supply and the ratings of the=20 MOSFETs, and the power that is radiated by the magnetic field of the=20 inductors.

With ideal components, at resonance, the voltage and current in the = series=20 circuit will approach infinity. It seems as if you are experiencing the=20 effect of breakdown of the MOSFETs or the capacitor, or limitation due = to=20 the inductor resistance. You should supply actual part specifications of = the=20 components.

If it is an actual circuit, I am surprised that it has not blown up! I=20 almost had that happen when trying to make a three-phase converter using = an=20 inductor and capacitor at 60 Hz resonance. Fortunately, all that = happened=20 was some arcing and a large current draw that dropped the line voltage = and=20 tripped the mains breaker.

Paul=20

Reply to
P E Schoen

Then I'll agree with Fred. The 6A is based on the remaining R when Xl and Xc cancel at resonance. Since it appears that you've retained the same inductors, that seems reasonable. Want more current? Rewind the inductors (larger wire).

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Don't hate yourself in the morning -- sleep till noon.
Reply to
Paul Hovnanian P.E.

Paul, I've almost got the feeling that Jessica Shaw is a bot. This has been going on for months with one turn or another to drag the comments either deeper or away. If "she" is real, she must have little education.

Reply to
John S

A bot would spell properly, and construct better sentences.

If "she" is real, she must have little education.

Much more likely.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)
Reply to
Fred Abse

Or use more volts ;-)

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)
Reply to
Fred Abse

Kind of depends on who made the bot, yes?

No doubt

Reply to
John S

has

comments

IIRC she is a software developer. Learning electronics without much expectation of understanding produces results like this.

?-)

Reply to
josephkk

'Splains a lot

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Reply to
Fred Abse

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.