Hi,
For D1-D4 I used a 35A bridge. Is that OK?
The "big" diodes on the PCB are the schottky's.
On your earlier drawing there was not a ground symbol. I guess this is just for the simulation and measurements?
Regards, Gerrit
For D1-D4 I used a 35A bridge. Is that OK?
The "big" diodes on the PCB are the schottky's.
On your earlier drawing there was not a ground symbol. I guess this is just for the simulation and measurements?
Regards, Gerrit
It should be OK. I am less sure about the big schottky's: they tend to have a large leakage. I'll try to simulate them in a realistic manner.
If the drop of the bridge is too small for detection, the solution could be the two-transistor alternative, or a prebias of the single transistor.
I am going to think about that, and test options with sims
If the drop of the bridge is too small for detection, the solution could be the two-transistor alternative, or a prebias of the single transistor.
I am going to think about that, and test options with sims
Naturally, readers will wonder whether the LEDs light up when the amount of DC present on the mains is "only" 249 mV [for 230VAC mains] or 124 mV [for 115VAC mains]. Numbers I extracted from Rod Elliott's article on Mains DC Blockers, posted on his Elliott Sound Products website.
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With the RBR30N40 of LTspice, the circuit still works, and provides a larger indication current:
Here is a tentative of prebias, to improve the sensitivity. A number of filters becomes necessary, to avoid an indication with just the 50Hz residue across the caps.
It is a first, clumsy attempt, and it could certainly be streamlined.
This is the LED current with no DC offset:
And this is the same with 0.5V DC offset:
Later, I'll simulate the two-transistor version
It is a first, clumsy attempt, and it could certainly be streamlined.
This is the LED current with no DC offset:
And this is the same with 0.5V DC offset:
Later, I'll simulate the two-transistor version
Here is the 2Q without offset:
Now with 0.5V offset:
This is without any prebias, meaning it is more tolerant.
A prebias could also be added if required, more simply than for the previous one.
Note that the sims are kind of worst case: pure resistive load.
With a transformer primary, the DC load resistance would be much lower, meaning the totality of the offset would find itself across the diodes, and would be more easily detectable.
Many other variations based on these circuits would be possible, depending on the needs and requirements
Now with 0.5V offset:
This is without any prebias, meaning it is more tolerant.
A prebias could also be added if required, more simply than for the previous one.
Note that the sims are kind of worst case: pure resistive load.
With a transformer primary, the DC load resistance would be much lower, meaning the totality of the offset would find itself across the diodes, and would be more easily detectable.
Many other variations based on these circuits would be possible, depending on the needs and requirements
On the pic of your test circuit, I just noticed that the transistor pinout suits types like 2N3904. If you used a BC547, C and E are reversed. Could it be the cause of the malfunction?
Hi Elvee,
You were spot on! I replaced the BC547B with a fresh one and reversed E and C.
Now the blue LED is off, regardless of loading with a lamp (50 Watt) or not. When switching the load on/off the LED sometimes peaks blue, so I guess it's working!
And even better: I inserted a 1.5 V AAA battery in the mains wiring and the led goes slowly to bright blue (with and without load). And without the batterij (but with a load) the LED slowly dims.
In that case it does not dim without a load. I guess the large capacitors keep the circuit alive?
Measuring the "old" BC547B shows that it's still intact. The battery survived as well without any harm done.
Regards, Gerrit
You were spot on! I replaced the BC547B with a fresh one and reversed E and C.
Now the blue LED is off, regardless of loading with a lamp (50 Watt) or not. When switching the load on/off the LED sometimes peaks blue, so I guess it's working!
And even better: I inserted a 1.5 V AAA battery in the mains wiring and the led goes slowly to bright blue (with and without load). And without the batterij (but with a load) the LED slowly dims.
In that case it does not dim without a load. I guess the large capacitors keep the circuit alive?
Measuring the "old" BC547B shows that it's still intact. The battery survived as well without any harm done.
Regards, Gerrit
Good to know that it ended working as designed, however I would recommend the 2-transistor version over that one: the overall complexity is globally similar, and the sensitivity is doubled without any help from a prebias circuit.
If you need an even higher sensitivity, I could also add prebias to the 2Q variant.
If the LED continues glowing after the load has been removed, it is indeed caused by the charge retained in the large caps
If you need an even higher sensitivity, I could also add prebias to the 2Q variant.
If the LED continues glowing after the load has been removed, it is indeed caused by the charge retained in the large caps
Hi Elvee,
The way it looks now it's quite sensitive. I may change to the 2-transistor later.
How about a resistor over each capacitor to get a little load on each capacitor?
Regards, Gerrit
The way it looks now it's quite sensitive. I may change to the 2-transistor later.
How about a resistor over each capacitor to get a little load on each capacitor?
Regards, Gerrit
It will do no harm, except if it is insanely low, but it will do no good either: in a regular appliance, the mains power switch will be upstream of everything else, meaning the LED will be instantly disabled as soon as you hit the power off switch
Hi Elvee,
Nevertheless I will do some tests tomorrow. I will report back my findings.
Regards, Gerrit
Nevertheless I will do some tests tomorrow. I will report back my findings.
Regards, Gerrit
I tried today with various resistors from 220 Ohm to 10K (one per capacitor), but I didn’t see any improvement (of difference).
Regards, Gerrit
Regards, Gerrit
Regarding the functionality, it should change nothing.
What should change is the behaviour when the circuit is disconnected from the load, but still attached to the mains: the LED should fade out more or less slowly depending on the resistor value
What should change is the behaviour when the circuit is disconnected from the load, but still attached to the mains: the LED should fade out more or less slowly depending on the resistor value