DC to DC Converters

[sidra khan]

i am using dc dc converter. i don't exactly know how it works internally. if anyone could suggest me some good reading material about it.. also i want to know if the input GND and output GND are isolated or not? i am using vicor dc dc converters

 

[Les Jones]

Most DC to DC converters work by first converting the DC to high frequency AC then passing it through a transformer to provide isolation and possibly a voltage change. The AC from the transformer secondary is rectified and possibly regulated. You can check it the one you have is isolated by connecting a multimeter set to a high ohms range. If it is isolated you should get an infinite reading. You could also look at the manufacturers data sheet for the item you have.

Les.

 

[sidra khan]

it is isolated one, i wanna know if i don't short the -ve output and input ground and want to use the -ve output as gnd for the rest of circuitry, how would i do it actually?

 

[Les Jones]

If you want to there is no reason not to connect input and output grounds together. Very often the reason for using a DC to DC converter is to have the ground isolated from each other. For example you may want to provide an RS232 serial link between some equipment that is earthed and connect the ling to a PC serial port. Without isolation this would form a ground loop. If the link was between different buildings then there could be a voltage difference between the two grounds that could couse corruption of data. Another application could be to provide a gate drive voltage to the top MOSFETs in an H bridge. To answer the question "how would i do it actually?" you would have to say what you are trying to do. The only thing you sould not do is to exceed the isolation voltage rating of the converter by having a larger voltage than tis between the input and output grounds.

Les.

 

[AnalogKid]

If you are asking about a Vicor J series half-brick, yes, it is fully isolated. And yes you can tie either input pin to either output pin - but only one pin at a time.

But if you don't need isolation, there are many DC/DC converters that will handle the same power for less money, heat, size, etc.

ak

 

[cowboybob]

it is isolated one, i wanna know if i don't short the -ve output and input ground and want to use the -ve output as gnd for the rest of circuitry, how would i do it actually?

I would suggest that you not do that.

Note page 3 of : http://cdn.vicorpower.com/documents/powertech/DC_Theory.pdf

Input and output grounds are carefully isolated from one another: defeating that isolation will likely destroy the device.

 

[sidra khan]

If you want to there is no reason not to connect input and output grounds together. Very often the reason for using a DC to DC converter is to have the ground isolated from each other. For example you may want to provide an RS232 serial link between some equipment that is earthed and connect the ling to a PC serial port. Without isolation this would form a ground loop. If the link was between different buildings then there could be a voltage difference between the two grounds that could couse corruption of data. Another application could be to provide a gate drive voltage to the top MOSFETs in an H bridge. To answer the question "how would i do it actually?" you would have to say what you are trying to do. The only thing you sould not do is to exceed the isolation voltage rating of the converter by having a larger voltage than tis between the input and output grounds.

Les.

i am using 24V and GND from external power supply at dc dc converter input. It converts 24V to 12V. Then i am using this 12V to drive the rest circuitry. As this is isolated converter, i am confused if the - output can be used as GND for driving the circuit. I am not connecting input and output GNDs to protect my circuit if anything wrong happens with external power supply!

 

[AnalogKid]

What you are describing is the most common way to use an isolated DC/DC converter, so there is no problem.

ak

 

[spec]

i am using dc dc converter. i don't exactly know how it works internally. if anyone could suggest me some good reading material about it.. also i want to know if the input GND and output GND are isolated or not? i am using vicor dc dc converters

A pretty good overview of switch- mode power supplies is here: https://www.electro-tech-online.com/articles/books-articles-data.758/
Item(1.11). Just download the pdf from the link.

Just to confirm there would be no problem connecting the positive output of your power supply to OV and thus generating a negative supply.

One thing to look out for with switch mode and some linear power supplies is they will not regulate the voltage with no load, so if you get any strange effects put a resistor across the output if the supply has no other load. A 20 or 30 ma load should do it. I have used many Vicor power supplies- they are good, but not cheap

 

[dr pepper]

This may not be what your looking for however it gives you a practical look into switchers without much confusing maths, excuse the title I make no inferences:

https://www.dos4ever.com/flyback/flyback.html