# high voltage DC measurement

Status
Not open for further replies.

#### sawaak

##### Full Member level 2
Hi,

I have few DC voltages upto 300V that I have to measure, using an ADC. Accuracy is not that important. I am trying to use the following circuit, need to know is that approach correct? and what things I need to consider to use this circuit?

Thanks,
sawaak

#### Integrated

##### Member level 1
Hi,

Keep in mind the input resistance of your A/D, (beacuse obviously you are going to use big resistors).... Also you may like to measure the current when voltage is passed through a resistor, but that depends on mechanical situation of your design.

regards

sawaak

### sawaak

Points: 2

#### uoficowboy

##### Full Member level 3
Also remember that most surface mount resistors have breakdown voltages of 200V or less. So be careful with your resistor selection! A small capacitor in parallel with your bottom resistor should also give you some surge protection as well as some filtering.

#### zeroskj1988

##### Member level 2
i think you can use 220k-1k combination to reduce the voltage level approximately to 1.5v. one thing u should remember is you have to use 1w resistor

#### atripathi

YOu may want to add varistors for protection against spikes. Although it would depends upon DC bus voltage nature.

#### ard

##### Full Member level 5
Lets work this backwards.

You have a maximum of 300 volts, to be pared down to a maximum of 5 volts.

Your ADC input shouldnt see an impedance of more than say, 4.7k. Then, the upper resistance in the voltage divider will have to be around 330k. This resistor would drop almost the whole 300 volts across itself, so the power rating works out to slightly over quarter watt. Therefore, a 1 watt resistor should be fine.

Hope I havent messed up the math.

Regards,

Anand Dhuru

Status
Not open for further replies.