Conversion of sinusoidal to spikes ?

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Externet

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Hi.
How can floating plain sinusoidal 230VAC 50Hz from a power transformer secondary be converted to 50Hz pulses of about 0.01mS duration ?
Thanks
 
Externet said:
Hi.
How can floating plain sinusoidal 230VAC 50Hz from a power transformer secondary be converted to 50Hz pulses of about 0.01mS duration ?
Thanks
Click to expand...
hi,

Half wave rectifier, zero crossing comparator and a monostable.
 
it is easier to get 100Hz and divide by 2. put a rectifier between the bridge and the filter cap. PNP emitter to regulator output, base to bridge through resistor and diode, collector resistor to ground give you 100Hz pulses.
 
What do you mean by floating? What is the secondary output being used for otherwise?
 
Hi.
Floating means none of the power transformer output winding terminals or lines is grounded, nor center tap neutral.
It is the output transformer of a DC to AC inverter, to be used for nothing else than to convert its AC into pulses for a device that operates with pulses and not with sinusoidal AC.
Miguel
 
If the transfomer output is used for other purposes and is not grounded then you would need to use an isolator, such as an opto coupler to generate the pulse. Connect the input of the opto coupler through a diode to the transformer output with a resistor to limit the current to the opto coupler's rated input. The opto coupler output can be used trigger a 0.01s monostable (one-shot).

P.S. And why are you against the deciBel?
 
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hi Carl.

The way I have used the opto method is to have the series resistor, you have stated, but a zener diode connected in parallel with the opto emitter.

The zener voltage chosen to suit the transformer secondary voltage, a 12Vac, say a 6V2.

This gives a good waveform on the opto collector and it also protects the opto against reverse overvoltage.

Regards
 
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Works, but I don't think the 6V2 zener will ever conduct in the reverse direction (foward direction of the opto emitter) since 6.2V is much higher than a typical emitter's forward voltage. You could split the resistor into two series resistors and connect the zener at the junction of the resistors. That way it would provide a clipped sine-wave signal to the opto emitter input.
 

The already isolated transformer output is not used for any other purpose than obtaining 230V 50Hz pulses, it has no grounded side.

I was expecting something more in the line of a dimmer/scr type of circuit suggestion where the scr conduction somewhere at the positive peak of the AC would capacitively emit the pulse (to be polished)

---> Feel that the antique attempt to substitute a perfectly good and world recognized unit as the Volt is senseless. The decibel is absurd in 2008 and makes all innecessarily convoluted and complex. All expressed in decibels can be perfectly expressed without it and with no confusion to learners.
 
The decibel is not intended to replace the volt. It is a logarithmic representation of power ratios (but is also often used to represent voltage ratios). The reason for using it is that a logarithmic measure is often much easier for humans to interpret, especially for relative measurements. It's also a sort of simple shorthand way of expressing such ratios. For example a filter rolloff of 12db/octave is simplier than saying a rolloff factor of 0.2512 per octave. Or it's easier to say an amp has 75dB of gain than a gain of 5,623.

I believe your chances of eliminating it's useage are about the same as eliminating the use of English units of measure in the U.S.
 
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Hello Carl.
Cannot see where is it easier
A decibel is the logarithm of a ratio.
If you know the ratio, it can be expressed that way, with no need to calculate its logarithm to say it.

An amplification factor of 20 already says it, There is no need to calculate the logarithm of 20 to say it. with the 10 or 20 factor added depending on power or voltage.
An operational amplifier gain is the Rf and Rin ratio, and is not given in decibels, why making life complex translating its gain to decibels...

A 0.6V signal does not need to be expressed as -2dBm, or in dBV, or dbu,...it is already 0.6V.

Seen many times, a ratio shown with a bunch of decimal places to imply is a hard to remember number, and compared to a decibel figure of perhaps a couple of decimals.
Example : For 7.4516443; its log= 0.87 Looks simpler with only 2 decimal places...
but it actually is 0.872252116. So the original ratio could have been comparatively expressed as 7.45 , nothing wrong with it.

No, I will not be able to eliminate its useage. Neither fluid ounces, furlongs, grains, acres, knots,....
 
Roff said:
AC couple the sinewave and you don't need the half wave rectifier.
Click to expand...

Morning Ron,
True.

Just didn't want to exceed the negative excursion rating of the comp input.

The 'floating' requirement suggests an opto coupler..

Regards
 
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Try doing the power budget calculations for a microwave radio link using your "learner friendly technique" and you will see why dB are so useful.

JimB
 
crutschow said:
I believe your chances of eliminating it's useage are about the same as eliminating the use of English units of measure in the U.S.
Click to expand...

True, but the difference here is that dB actually make sense.

Sorry Externet, but you have failed to present a convincing argument. While I agree that old-style Imperial/English/American/whatever measurements are goofy*, I don't agree that they are a good analog to decibels. Sure, if you contrive to attempt to use decibels as though they were volts you will make it look like decibels are silly--but then, if you were to contrive to attempt to use volts as though they were decibels, you could make the same argument the other way--that *volts* should be abolished. They are different entities and are used for different things, although there is some overlap which is why a contrived example appears to make dB look useless.

* That being said, for some reason I tend to think of my height and weight in inches and pounds, not centimeters and kilograms. The rest of the time it's SI all the way.


Torben
 
Am I missing something here? If the output of the transformer is used for no other purpose, why can't one terminal be grounded?
 
JimB said:
Try doing the power budget calculations for a microwave radio link using your "learner friendly technique" and you will see why dB are so useful.
Click to expand...
Part of the reason dB's are useful is that, since they are logarithmic, they can be simply added in your head to get a total. Thus, for example, an amp stage with 32dB gain driving an amp stage with 36dB gain will have a total gain of 68dB. You don't have to multiply 39.8 by 63.1 to get the total gain of ~2,500.

Ethernet, if you ever work with designing any type of amplifiers, not just microwave, you will see the advantage of working with dB. It simply makes the work easier.
 
Roff said:
Am I missing something here? If the output of the transformer is used for no other purpose, why can't one terminal be grounded?
Click to expand...
Ron. Couldn't agree more. That's why I suggested it in my June 26th post, but guess most people missed it.
 
crutschow said:
Ron. Couldn't agree more. That's why I suggested it in my June 26th post, but guess most people missed it.
Click to expand...
This is not intended to be contentious, but if you suggested it, it was in a roundabout way, unless I missed it again when I reread your posts.
 
Roff said:
This is not intended to be contentious, but if you suggested it, it was in a roundabout way, unless I missed it again when I reread your posts.
Click to expand...
It was sort of buried in the quote from Ethernet:

ETHERNET QUOTE: The already isolated transformer output is not used for any other purpose than obtaining 230V 50Hz pulses, it has no grounded side.

(My Reply in blue in the quote): In that case you ground one side of the output and use the suggested comparator, one-shot circuit.

So guess my reply wasn't that obvious.
 
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