Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Sensisng AC supply line and coparing it with a comparator

Status
Not open for further replies.

papaisou11

Member level 2
Joined
Aug 2, 2016
Messages
47
Helped
0
Reputation
0
Reaction score
1
Trophy points
8
Activity points
486
Hiii...

I want to make a 12V ups system for powering up my musical gadgets.

My requirement is When the AC Voltage (230V, India) is present the 12v will be produced by a SMPS and it will provide the 12v power.

As the SMPS has an universal input voltage rating, which is 85V AC to 230V AC, if there is no AC input or the input voltage is below 85VAC, a Boost regulator which will be turned on and provide 7.4V to 12V at the output and will power up the gadgets. This switching will be done by MOSFET which will be connected across the boost regulator input pin.

I already made this circuit, but the problem is about sensing the AC line. I tried to sense the AC using diode bridge, Filter caps and opto-coupler but facing difficulties related with the 85V AC. If I want to compare the converted DC across the diode bridge using comparator, what is the best way to wiring it?

Is there any alternative way to do that?

Thanks in Advance.
 

What, exactly, is the problem you are having? If you've got a DC voltage it should be a simple task to compare it to a fixed voltage. But, first of all, I recommend you don't go directly to your 230VAC; I'd use a step-down transformer; just to be safe.
 

I already made this circuit, but the problem is about sensing the AC line. I tried to sense the AC using diode bridge, Filter caps and opto-coupler but facing difficulties related with the 85V AC. If I want to compare the converted DC across the diode bridge using comparator, what is the best way to wiring it?
So what exactly are the problems you are having with detecting 85Vac?

Below is the LTspice simulation of a circuit that may work for you.
The rectified waveform goes directly to the opto input (note that low voltage diodes can be used since the maximum reverse voltage is just the opto LED input forward voltage drop with the rest being dropped across the resistor).
The filtering to get the average dc value of the waveform is after the optocoupler.
The average value is less affected by noise and spikes on the line as compared to the rectified peak value.
The DC value for the normal 230Vac input can be linearly extrapolated to determine the comparator voltage for 85Vac, i.e. the 85V dc voltage is 85/230 of the 230V voltage.

Capture.PNG
 
Last edited:

Hii...
barry and crutschow...

I have the schematic... please see the attachment...

I used a comparator to save the battery from deep discharge, as it will turn down the mosfet connected across it and also break the Battery supply line to the boost regulator input. I connected the optocoupler out at a reference voltage point across the op-amp, so when the opto-coupler light up it will make one reference voltage as 0 and as a result the mosfet will turn on. I am unable to make a AC reference voltage point using opto-coupler so planning to using a different comparator and make this happen.

Is it possible to cut the opto-coupler at 85VAC point or below and set a threshold point?

Thanks once again.

Schema.png
 

Hi,

These are only snippets of your circuit.

I recommend to focus on one item first: The AC sensing. (Don't talk about battery voltage sensing or something else, it just confuses)

With your AC sensing...I see just an optocoupler and series resistors.
But there is no conversion to DC, nor is there some threshold circuit.

Rectified AC is 100 (or 120) times per second "zero" and 100 times per second high voltage.
And similar waveform is the optocoupler input current (in your case).
The optocoupler will transfer the input current to an output current.
Thus the output current will be: zero... rising to a maximum ... falling to zero ... rising to a maximum....
Continously.
So if you use a threshold at this AC signal you get a ON, OFF, ON, OFF...signal as result.
To avoid this you need to filter the rectified AC signal to get a DC signal.
Then you need to decide at which level of DC voltage you want your threshold.
--> use resistive voltage dividers and zener diodes to create the threshold.

Use a simulation tool to test your circuit.

Klaus
 

Hi...

Thanks for your reply KlausSt. I Filtered the Rectified Dc across the pc817 optocoupler and used the circuit described by crutschow. Now I can use the gain pot to adjust the desired average voltage and create a ratio of Input Voltage vs Optocoupler transistor output voltage.

Is it ok to connect the optocoupler output to this comparator or I should choose another one? can I combine this with the deep discharge cut-off comparator?

Thanks.
 

Is it ok to connect the optocoupler output to this comparator or I should choose another one? can I combine this with the deep discharge cut-off comparator?
What comparator?
What's a deep discharge cut-off comparator?
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top