5 - 220 volt AC/DC to stabilized 5 volt DC

I have a PLC which use stabilized 5 DC input.
I want to add a device that can convert 5 - 220 volt AC / DC to stabilized 5 volt DC.
in order to make a PLC operates in more flexible way, I find schematic about voltage indicator. here this scheme :


Parts:

P1 = Red Probe
P2 = Black Probe
D1 = 5 or 3mm. Red LED
D2 = 5 or 3mm. Green LED
LP = 1220V 6W Filament Lamp Bulb

if i replaced LED with optocoupler, will it be reliable? does any one have better solution?

It isn't clear what you are trying to achieve. If you want to sense if the 220V AC is present, yes you can use an opto-coupler but replace the two LEDs with a bridge rectifier and connect the opto-couler across the DC output. If you put a reverse voltage across a normal opto-coupler LED side it will be damaged, the bridge rectifier will ensure it only sees the correct polarity for it to conduct. The output will be pulses at twice the AC frequency.

There may be a flaw in your design though, bear in mind that when the filament of a lamp is cold it has a much lower resistance than when it is glowing. At the moment you connect the probes there may be a much higher current flowing than you expect and the LEDs or opto-coupler could be damaged.

Brian.

There may be a flaw in your design though, bear in mind that when the filament of a lamp is cold it has a much lower resistance than when it is glowing. At the moment you connect the probes there may be a much higher current flowing than you expect and the LEDs or opto-coupler could be damaged.

Click to expand...

A similar design using a NTC instead of an incandestent lamp has been sold by german company Steinel since the 70th. But the NTC has about 4k cold resistance, and the device is specified to reach 1 - 1.5 mA after 3 ms. An inrush current peak of this magnitude is apparently handled by regular LEDs. Depending on the specification, an additional clamp circuit may be advisable for an sensitive opto coupler.

But either a lamp or NTC will be stressed by each inrush event. I won't suggest the design for continuous operation. I would rather go for darlington opto couplers and low drive current.

i apologize for my confusing explanation,
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basically, i want to make some device that operate as shown at picture above. (marked with red)*
this device senses / converts 5 - 220 volt AC / DC to stabilized 5 volt DC. this 5 volt dc current source will supply PLC input.

then i googling and find something that have close similarity with the project I am working on.

**broken link removed**
in this schematic, i haven't found compatible component yet (which operates at 5-220 volt)

device that i need may be a voltage sensor, anyway a converter will also suits me as well

I explained, why a similar design, that may be suitable for a voltage probe, shouldn't be used in continuous operation, e.g. for a PLC input.

For similar problems, I followed these considerations:
- the power dissipation should be limited to a reasonable amount, e.g. < 500 mW, better < 250 mW. This results in a maximum input current of 1 - 2 mA.
- input currents of this size can be used with sensitive optocouplers (darlington output)
- for a smaller voltage ratio, e.g. 24 - 230 V, I used a simple current limiting resistor (470K), resulting in a very low input current in the low voltage range, but it's still possible
- extenting the voltage range to 5 - 230 V (about 1:100 effective current ratio) rather suggests a constant current circuit, e.g. using a depletion mode MOSFET

Please clarify - are you monitoring the source or are you trying to power the PLC from it? I can't understand why you want 5V stabilized out of it if it isn't for powering circuitry.

If you are trying to use an opto-coupler to couple the power source it won't work, they can give an indication of voltage present at their inputs but they do not actually pass appreciable power to the sensor side.

Brian.

Do you have an idea what could be the current value of the "Stabilized 5 Vdc". Is it constant? If not, what are its maximum and minimum?

At the input, is the AC frequency 60Hz, 50Hz or other?
I assume you mean 5 - 220V if AC as RMS value (so the peak voltage is higher than in case of DC).

I guess, you don't mean looking for an AC zero-crossing detector that gives a precise trigger 5V pulse (less than 100us offset) for a wide range of input voltage (say 100V to 250V) and not sensitive to temperature and by using low-cost components... Am I right?

Kerim

how to implement depletion mode MOSFET in this project?

my PLC is using 220 VAC power source. a stabilized 5 Vdc for discrete signal input. because a limit switch in my experiment is using 220 Vac/50 Hz and many sensor using 5Vdc, i probably need this device (5 - 220 volt AC/DC to stabilized 5 volt DC).

Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. With values 5 V DC representing On, values below 1VDC representing Off. i am using "stabilized" term because it probably will damaged the plc if the voltage input unstable. For on condition, the current of discrete signal is less more than 4mA.

is 5 - 220 volt AC/DC to 5 volt DC converter (sensing voltage) possible to create?

Just to be sure, don't you think that the experiment needs a sort of electrical isolation between the mains AC voltage and the PLC (by using an optoisolator for example)?