How to measure and step down 350 VDC.......

[aherna77]

Hi,
I am working on a project that is requiring measuring 350 Volt DC to be input into an FPGA which only takes 3.5 TTL volt. I am think this is like a digital multimeter but without the Ohm meter. So my question is what should I use to measure such high voltage and how do I step down this 350 VDC? Is there a IC that could do this function? Can you please help me! Thanks..

v/r,
AA

 

[MikeMl]

Is there an A/D input on the FPGA that you are using to "measure" the 350V level, or are just trying to make a "binary" measurement; i.e. the 350V level is there or not?

 

[aherna77]

Yes. ADC is connected to the FPGA. Question? Does the ADC can take an Input of 350 VDC?

 

[aherna77]

I am trying to do both, measuring the 350V levels and to convert it to binary. The objective is to monitor a line that has 350vdc but I don’t know what technique to use

 

[MikeMl]

Yes. ADC is connected to the FPGA. Question? Does the ADC can take an Input of 350 VDC?

Not just no, but hell no!!!

Read the data sheet on the ADC, then come back if you still have questions.

 

[crutschow]

You just use two resistors in a resistor divider network to reduce the voltage. For example a 690kΩ resistor connected in series with a 10kΩ resistor between the 350V and ground (10kΩ to ground) will give 5V for a 350V input.

 

[aherna77]

That’s right a voltage diver will be ideal if I only need to convert to 5 Volt. However, What I am trying to do here is to monitor a dc line of 350 vdc but what will happen when the voltage changes from what level to other. It is not just a simple voltage diver. I need to design a circuit that capable of monitor the dc line changes like a digital multimeter.

Thanks...

 

[aherna77]

MikeMI,
Do you know anything on step down transformer or dc to dc converter?

 

[aherna77]

MikeMI,
Do you know anything on step down transformer or dc to dc converter?

 

[crutschow]

That’s right a voltage diver will be ideal if I only need to convert to 5 Volt. However, What I am trying to do here is to monitor a dc line of 350 vdc but what will happen when the voltage changes from what level to other. It is not just a simple voltage diver. I need to design a circuit that capable of monitor the dc line changes like a digital multimeter.

Well, if you told us everything at the start we could come up with better answers. We are not psychic.

So what is the range of DC voltages you want to measure and to what precision?

 

[mneary]

You have a 5V FPGA? Look again; these are unusual these days. It'ss likely to have 3.3V I/O.

 

[tcmtech]

Use an off the shelf universal voltage (100 - 250 VAC input) SMPS from a common cell phone charger or other low voltage device to step the DC voltage down to the actual voltage the monitoring system needs for power. Then use the simple resistor divider to get the right input voltage range for the device to reference from.

The universal voltage power packs change the incoming AC into DC before they transform it down to the final output. That DC part of the circuitry actually works on a 140 - 400 VDC input without any problems.

 

[aherna77]

Gents,
Thanks so much for all your help! I finally got it thanks to all of you. A simple voltage diver was the solution. I want to apologize for my lack of knowledge.
Thanx…
AA