DC-DC Isolation using HCNR200 - Page 1
Forum section: electronics / projects

author: ajoseph88
author_rank: Contributor
timestamp: October 27, 2015, 09:55:11 pm
content: Hello Guys....I was told on this website to use HCNR200 for DC-DC isolation... And attached is the circuit for positive polarity voltage using HCNR200...I have a doubt regarding this circuit... As the notes say, you should use two separate LM158 op-amps, which is fine...But what about the Vcc (supply) to the left side and right side in the picture.... it reads Vcc,GND1... and Vcc1 and GND2... so is it two separate power supplies... if Yes... can you explain that please... I mean, I only have one power source using LM705, which gives 5V, which i have taken from one of the tapings of the transformer... There are no tapings on the voltage transformer that I can use.... So is it a must, that i should buy an extra transformer, rectify it and put a voltage regulator for the Vcc1 and GND2, if i am using the present to power Vcc and Gnd2...Have anyone used this HCNR200 for DC-DC isolation... can you experienced engineers help me regarding this...Thank youJoseph Dawkins...

author: daqq
author_rank: Super Contributor
timestamp: October 27, 2015, 10:01:44 pm
content: The point of galvanic isolation of signals is to make sure that no point in any part of one circuit is electrically connected to the other - as such if you are isolating a signal you also need a separate ground reference for it and also a power supply for it. If you used the same GND and VCC for the isolated part, it would not be isolated at all, defeating isolation alltogether.You can use various isolated DC DC converters to get an isolated (floating relative to the input) +5V - like these fellas:http://assets.tracopower.com/TMA/documents/tma-datasheet.pdf

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: October 28, 2015, 12:11:39 pm
content: its not clear that you need isolation - maybe just attenuation or a differential amp to reject some common modeyou really need to describe the problem a bit better - what does the larger system look like, what are you measuringisolation amps amps are a good solution for measuring small V riding on large, noisy V that need too much common mode rejection, perhaps over too wide a frequency range for a diff amp

author: ajoseph88
author_rank: Contributor
timestamp: October 29, 2015, 01:21:34 pm
content: Quote from: daqq on October 27, 2015, 10:01:44 pmHello DaqqI have the tapping's of the transformer as seen in the diagram attached...So, as to my knowledge, x0 is common GND to x1, x2 and x4.And x5 and x6 are separate or isolated from the rest. So If I am able to put a diode bridge rectifier, then capacitors, then LM7805 across x5 and x6, the same way as i used across x1 and x0... Does that give two separate isolated power supplies, that i can use for HCNR200 left side and right side... Does that provide galvanic isolation...

author: ajoseph88
author_rank: Contributor
timestamp: October 29, 2015, 01:25:53 pm
content: Quote from: f5r5e5d on October 28, 2015, 12:11:39 pmI am measuring the voltage from the armature of a 200V D.C motor... So I pass it through a low pass filter, then use voltage divider, to reduce the voltage to about 0 to 4V... and give it to a microcontroller... so i get a linear 0 to 4v range as the voltage in the motor varies from 0 to 200v... but its not isolated... and last time i blew up the breadboard and some wires trying to measure the 4v output using oscilloscope...So that's why i am trying to use HCNR200 to get isolation... and the datasheet claims its highly linear...