Miniature Transformers of Isolated DC-DC Converters

I have looked around and your price is far too low it is going to be more like $5.00/unit.

DC-DC converter for $5 each is OK but switching transformer need to be only $1. Perhaps 100kHz to 1MHz switching frequency will require very small core and few truns and that is what I need.

Best of luck looking but you have set an impossible task.

I found that Texas Instrument is making a DC-DC converter for $5 with dual output and is as small as I wanted. The order goes to Texas Instruments for 1000 numbers now.

I hope they meet with your approval.

Yet to test them. Yes I had bad experience with Texas ICs and have lots of bad parts got shipped all the way from USA. I can not say anything unless I test the parts. Right now their specs are only reference.

You might be able to do it if you wind your own. I'm not completely sure how to do it cheaply for 3000V isolation, though. The core cannot be bare ferrite, first of all. I tend to think getting high voltage isolation and low leakage inductance are competing needs. I have been experimenting with zero voltage switching to eliminate much of the concern over leakage inductance.

How much output current at +/-6V ? Output tolerance? and other specifications.

80mA to 100mA with current noise less than 0.1%. Isolation 1500V.

Even if you do manage to do it you will have to keep duty cycle in mind.

Have you tried contacting any of the strobe light manufacturers? They do use these miniature transformers to boost say 6 vdc to 330 vdc. They might be able to help you.

1500 v isolation is a different matter though.

Sir, Switching frequency is very important. Are trying using any Tiny switch of Power Integrations? Take trials with Toroid Ferrite cores (or beeds) that are used as input/ out put filters (even small beeds are available at very low cost in the market). Since conversion is from 30V DC to 6 V DC number of turns will be very low and also wire guage.Though winding is a bit difficult the size and efficiency will be very high. It is also possible to achive high isolation.

These good thoughts got me to remember a trick I thought of for low power converter transformers. It basically eliminates trouble with winding low power transformers.

Obtain some of those clamp-on choke half-toroids. Cover each half carefully with enough film tape for isolation. Winding each half is easy. Even small gauge wire is easy by hand since you can wind around and around without having to thread through a continuous core.

Once the halves are wound, cover them with enough extra tape for more isolation. Press the halves together and hold them together tightly with a nylon tie.

I found this way to work excellently for my low power isolated converter. Thanks for the memory jog!

Yes, you did it rightly and that metal film gives good shielding and reduces leakage to other windings. My aim is to get to about 1nA leakage current. Hence, Teflon wires and some shielding etc. MHz switching to reduce the size and go for high current to several amps in the primary.

Good Idea. I have developed a program that computes the transformer design and it was published in electronics design is also available on my web page. This helps in computing number of turns for a frequency and core size. I think that high frequency ferrite core will do wonders at 1MHz to 2MHz frequency range. I can use Teflon insulated core and wires to get 6kV isolation easily.