# Output voltage monitor circuit ideas

• posted

Hello Group, I am looking to designing an output monitor circuit for a power supply with up to 10 outputs. These outputs could be from 2V to 48V The input supply for the circuit must not be above 28V 2A The output will be LEDS lighting to show that the output has dropped out. Must have a quick response time, if the output drops out for a few ms I need to know about it.

I was thinking a comparator type circuit comparing output with 0V and then an LED switching on to alert the user that the output had dropped out. Any other ideas or circuits?

Thank you Dan

• posted

There is no concept of anything other than ON or OFF, and that's final- so why do you want to complicate the issue by asking all those questions!!!!!! LOL.

• posted

How do you define "drops out"? Comparing with 0V is probably not what you want-- with perfect components it will never get to zero.

Maybe you want a voltage divider (dividing the output voltage down to something around 1.3V, then compare against a ~1.25V reference, and trigger a one-shot of ~0.5 second to blink the LED even with a short drop of a few % from nominal.

But why do you want to do this? Why would the voltage drop? Is there a better solution than just detecting this mystery drop (due to mechanical contacts or something?).

Best regards, Spehro Pefhany

```--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com```
• posted

A
• posted

Dan, I don't think you want to compare the output voltages to 0V. What if the output voltage just sags below a specified voltage; not necessarily going all the way to 0V... wouldn't you want to know about that as well? What constitutes a drop-out? The voltage falling all the way to 0V, or below a specified threshold? A bank of LM339 quad comparators would probably do your job. Three chips, and you even have a couple comparators left over. Make a reference voltage source of about 1V, and scale the power supply outputs to 1V. Connect the reference to one comparator input, the scaled outputs to the other. Send the comparators' outputs into 555 one-shots if you want a momentary flash when the voltage drops. If you want the LED to latch on when the comparator trips, send the outputs into a D-latch. Of course, the LEDs connect to the 555 flasher or to the latch output. That should do it.

```--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the ```
• posted

Hello Dan,

Comparators are a good option but don't compare with 0V, use something higher. All comparators have offset errors. Also, as Spehro mentioned you might need to decide for each output a level below which you'd consider it "dropped out". IOW, where the connected circuitry would quit functioning.

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Regards, Joerg

http://www.analogconsultants.com```
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Opto's holding SCR's off. Ed

• posted

Hello I do Halt (highly accelerated Life Testing) on varying power supplies. This involves stressing units to extremes of temperatures and vibration testing. I want a one trick box that will work for all power supplies with up to 10 outputs. I see what u r saying with the regulation issue. Ideally I would measure about 2% output dips but comparing with a 1V regulated signal would do as a minimum. I was trying to keep things as simple as possible for the initial ideas but as you ask, This is what I would like to achieve: 98% of the output voltage at switch on would need to be stored and used for the comparator signal with the actual output voltage. then triggering an LED with an easy reset option.

Spehro Pefhany wrote:

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