1) Who won’t “allow” you to plug a small transformer into the mains? If this is just a hobbyist thing, stop worrying, we’ll visit you in jail. If it’s a product, that’s different.
2) the circuit doesn’t know anything about plug orientation.
, it just knows about voltage.
3) it depends.
4) If you set your hysteresis large enough, you won’t get false triggers.
you could save yourself a chip by using a Schmitt-trigger NAND gate instead of an inverter and AND gate.
Hi,
Why it can't work.
TR1_N2 has no relation to your GND, thus ZCD circuit sees no voltage. You need to connect N2 lower side to GND.
I don't understand the relay function. When there is no supply the ZCD won't work. If there is supply the relay will always be ON.
SD1 and SD2 are in parallel. A single diode will do.
But the diode limits negative voltage but does not limit positive voltage. So the signal is non symmetric...take care not to make the ZCD output unsymmetric.
LM193 input voltage range is -0.3V .... can you satisfy this?
The input of both comparators are at same voltage nodes, thus they switch equally...just inverted.
No filter, no hysteresis...this calls for noise pickup.
What do you want to do with the ZCD signal?
Klaus
Both your comparators switch at around 0V ... consider noise and offset.The idea is to have no signal going into the comparators until the regulator is regulating and the power supply is functioning correctly, so that the ZCD circuit is ready to accept input signals.
Yes, this is non symmetric. 3V vs about 0.5V.Positive input will be limited to e.g. 3V, negative input to the Schottky diode Vf.
If it´s 0.35V then you´re out of abs. max specification. "Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device"not sure about satisfy LM193 datasheet specifications regarding -0.3V max.
This is why I asked about the application.wouldn't adding a filter create further delay between the actual zero crossings and the output signals used to trigger whatever is supposed to turn on as close to the zero crossings as possible?
yes, I´d start with 2nd order.would an x-order band pass be the simplest way of dealing with these issues?
Hi Klaus,Hi,
No problem. It's your design ... and you have to find and go your own way.
Give the same task to 10 engineers and get10 different solutions.
Some thought about your design.
You take much effort in adding several Opamp stages.
In my eyes the stafes U3 and U4 don't bring any benefit.
If U4 can drive the signal, then also U2 will be able.
U3 is just an inverting circuit ... for a symmetrical AC signal .... the comparators won't care...
Klaus
Hi Dick,You might be well off to use a small xfmr
to sniff the line without letting line into
active circuitry.
Comparator chatter after the zero crossing
event is not necessarily a problem, like the
time I had to do this was just to fire SCRs
in a DC motor drive bridge and it doesn't
matter how many times you poke a SCR's
gate terminal, the first one gets it done.
In timing applications w/ ramp and comparators
I will always use a SRFF to clean up chatter.
A one-shot can be a way to go if you know
how much noise amplitude and duration to
expect.
Is there a reason why you need to get fast
ZC impulses rather than edges? Simpler to just
use a square wave image of line and just get
the ZC-up, ZC-down off those two edges, if
adequately clean (what constitutes adequacy,
the successor circuitry gets to say).
The band pass filter inverts te input signal. True. But at a perfectly inverted signal the zero cross still is at the same place as before, just rising edge becomes falling and vice versa.Explain it to me in 'stupid', please, because I'm not sure if I'm missing/misunderstanding something... If the band pass filter (U2) inverts the input signal 180º, by my understanding and reasoning I would add an inverting amplifier stage (U3) to invert that inverted signal another 180º to make it the same as/in phase with the input signal. Thus, my 'rising zc' and 'falling zc' are not inverted at their outputs, because if I left the input signal 180º out of phase with the input, the 'rising' would really be the 'falling' zero crossing and vice versa. Is there something wrong with my reasoning about that?
I'd say the additional buffers make things worse, especially regardingI always have doubts about op amps with feedback and when/if the previous and subsequent stages that may also contain feedback or voltage dividers, etc., will affect their operation, so I shove buffers everywhere, just in case. So U4 is unnecessary, but U1 is necessary?
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