Maybe not; the doorbell is not intended for short risetimes, it has thick laminations in its iron core. It'll generate a moderate turnoff voltage spike, but not a fast one. The flux in iron decays a lot slower than in ferrite.
s
ive
of a
e >current through the TRIAC is the same current through the bell coil. Bec ause >the bell coil is inductive, its current lags...
ff voltage rate of rise.
spike, but not a fast one. The flux in iron decays a lot slower than in
It's not the core responsible for the dV/dt, it's the TRIAC. When the TRIAC shuts off, the current is zero, making the coil core flux ideally zero. It is the line voltage that instantly switches from being across the bell to being across the TRIAC which is attempting to block the circuit. Neglecting stray bell coil capacitance, the coil has no problem with an instantaneous voltage change.
So would I be right in thinking that I can simply run sims with varying values of C until I and V in/across the coil are back in phase? Will that do it?
Rather than mess with all this stuff, why not use the bridge rectifier and a transistor? Then you can cut the power on or off as you see fit and don't need to worry about the dv/dt stuff.
I take it you aren't actually going to reduce the power to the bell, rather it is just on and off, right?
-- Rick C
a ,
Just draw up a series R+L+C and AC- 50 Hz sine input circuit. Your R is 4k ohms, make L-10H, and C=0.1u, set the initial phase for the sine at +45o and run the transient simulation out to say 20msecs. Probe the voltage acro ss C and check that it's max slew is well less than 30V/us, maybe 3V/us, th en you should be safe.
TRIACS are much more rugged than any transistor.
he
it
s a
er,
at
k ohms, make L-10H, and C=0.1u, set the initial phase for the sine at +45 o and run the transient simulation out to say 20msecs. Probe the voltage ac ross C and check that it's max slew is well less than 30V/us, maybe 3V/us, then you should be safe.
And give that sine a 220/0.7=315 V peak amplitude.
If it is an external telephone bell, the normal AC power line feed may be too high frequency. The classical POTS ring signal was about 100V at 20 Hz.
-- -TV
Sorry, but what the hell kind of application is it where you do not need isolation ? It's hard to think of one really.
At least he would be able to get the transistor circuit to work easily.
-- Rick C
I think you're right. In may not matter. If the bell/buzzer has a commutating switch in it, the next OPEN phase of that switch will cut it off regardless of a triac false-trigger issue, anyhow.
10 Henrys sounds an awful lot - but I can measure the real thing and assign that measured value to L in the sim. Cuts down the scope for error.
So it's all about getting the AC voltage slew rate down to
It doesn't.
You said isolation from the phone line/phone system. I repeat: not necessary in this instance as it will not be connected to the phone system.
This one has been proven to work fine at 240VAC 50Hz during extended testing.
Julian, Your post has proven to be a reading comprehension test >:-} ...Jim Thompson
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That would certainly account for all the misunderstandings, Jim!
Nothing dramatic, the TRIAC simply fails to turn the bell off, no smoke with your high impedance load.
Yeah but then you might have to shoot the thing. Ammo is expensive.
there's cheaper SSRs digikey.http://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/CPC1972GSTR/CLA273CT-ND/1277147
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