voltage window switch control circuit with hysteresis 2

[ijaoga]

I am looking for information on the design of a voltage window switch control circuit with hysteresis.The device is expected to control a 50V dc back up power supply for a telecommunication equipment.The device should be able to switch on a dc back up at 50V and off at 46V.The problem i have is with the hysteresis loop.I will be grateful if anyone could help me find a solution to this problem.

ijaoga

 

[BrianG]

It may be just a typographical error in your message, but could your problem be that you have the requirement of the window comparator defined the wrong way round? If you have a 50V normal supply surely you want the backup supply to cut in when the normal supply drops to 46V. The backup supply would then be set to switch out when the normal supply recovers to around 50V.

 

[ijaoga]

BrianG,

Thanks for your response.It seems you did not get my message correct.The word hysteresis suggests that the circuit should have a temporary resistance to change in voltage.The device should still be on if there is a change of voltage from 50V to 47V,but must go off at 46V and below.I hope this has made it clearer.I look forward to more response from you.

 

[nbucska]

Can't you just diode-OR the two supplies? (whichever is higher, gets the load ) <nbucska@pcperipherals.com>

 

[pebe]

ijaoga,

BrianG is right. A backup supply takes over when the normal source of power fails. So as written, your request doesn't make sense.

 

[ijaoga]

pebe,

I think your post should have been more helpful if you try to find out what hysteresis is all about.

 

[BrianG]

ijoaga,

You seem to be overly concerned about the word &quot;hysteresis&quot;. In design of comparators it is intorduced to ensure clean state switching without oscillation, which may otherwise occur if the input voltage dithers around the threshold voltage. This is normally achieved by positive feedback, which shifts the reference voltage by a pre-determined amount as the comparator changes state. This makes the comparator switch at two different voltages depending on direction of change at the input and thus introduces the hysteresis.

You state that you are trying to monitor a 50V supply system and provide a backup supply, so from the figures you have given the lower threshold for the falling voltage is 46V and the upper threshold for a rising voltage needs to be just slightly below 50V, thus you have about 4V of hysteresis.

I have designed a comparator circuit which meets these requirements and tested it with the Simetrix circuit simulation program. If you let me know your e-mail address through these pages I can send you a Word document showing the circuit diagram and the hysteresis response graphs.

 

[pebe]

ijoaga,

I am well aware of the meaning of the term 'hysteresis', having been in the electronics industry for many, many years!

The point I was making was that you appeared to have the voltages 50 and 46 the wrong way round in both your earlier postings.

That has absolutely *nothing* to do with hysteresis!

 

[melone]

ijoaga,

Try looking at how a schmidtt-trigger device is designed. Maybe that will get you started. BTW, are you trying to prevent your circuit from smoking by switching to 46V when your other supply exceeds 50V? Also, what reaction time is acceptable for these events?

 

[ijaoga]

BrianG,

Thanks a million for your concern in finding a solution to my design problem.My e-mail address is ijaoga@yahoo.com or ijaoga@hotmail.com.

 

[ijaoga]

melone,

The purpose of the design is to control ONLY BACK UP.

 

[naikjt]

The Best Solution is using a PIC with an A2D..

Have the PIC Measure Voltage at Approx. 10ms rate and
HAve it perform Hysterisis Locic.

Note YOu can us Timers in pic to provide Time Delay Etc.

Jay.

 

[melone]

Other than going negative at 46V, when would your back up battery ever turn off? Re-read your posts and see if you can figure out why we are having a tough time figuring out EXACTLY what you want. You said that &quot;device should be able to switch on a dc back up at 50V and off at 46V&quot;. Alright, at 46V, turn everything off, but when is your primary power source ever going to supply any power?