Hello,
I need to build an isolated DC-DC converter for a project. It's going to be a one-off so my requirements are mainly ease of building and simplicity.
Requirements:
- Low noise - it is going to be used in my class D amplifier (it's part of an experimental gate driver design I'm trialling)
- 12 volts in, 2 x 12 volts 1 amp out
- Easy to wind transformer - not thousands of turns
- Fully isolated output
I know there are three topologies I should look at - flyback, push pull or forward. In layman's terms, what is the difference between these topologies and which one should I be looking at to suit my requirements?
Cheers.
I need to build an isolated DC-DC converter for a project. It's going to be a one-off so my requirements are mainly ease of building and simplicity.
Requirements:
- Low noise - it is going to be used in my class D amplifier (it's part of an experimental gate driver design I'm trialling)
- 12 volts in, 2 x 12 volts 1 amp out
- Easy to wind transformer - not thousands of turns
- Fully isolated output
I know there are three topologies I should look at - flyback, push pull or forward. In layman's terms, what is the difference between these topologies and which one should I be looking at to suit my requirements?
Cheers.
Hi,
OK, I have looked at that (and others) and done a bit more research.
I think I want to use the push-pull topology, however...
I need two isolated outputs from the same supply. However, I think feedback is going to be a problem - am I right in thinking I can't have feedback on just one of the outputs, in case the loads on each output are unequal?
What are the problems with running a push-pull converter open loop with no feedback at all? Surely unlike with a flyback converter, the secondary voltages will be fairly constant and won't just keep rising unless the duty cycle is 'throttled back'?
I am visualising it as a smaller, higher-frequency version of a mains transformer - is this the right way to think about it?
OK, I have looked at that (and others) and done a bit more research.
I think I want to use the push-pull topology, however...
I need two isolated outputs from the same supply. However, I think feedback is going to be a problem - am I right in thinking I can't have feedback on just one of the outputs, in case the loads on each output are unequal?
What are the problems with running a push-pull converter open loop with no feedback at all? Surely unlike with a flyback converter, the secondary voltages will be fairly constant and won't just keep rising unless the duty cycle is 'throttled back'?
I am visualising it as a smaller, higher-frequency version of a mains transformer - is this the right way to think about it?
The Application Note might help you with your design.
http://www.ictest8.com/eg/tl494_ap.pdf
You normally only use feedback from one of the secondaries.
http://www.ictest8.com/eg/tl494_ap.pdf
You normally only use feedback from one of the secondaries.
The transformer core is chosen from the frequency and power that you require.
A typical choice would be something like an ETD core. You then need the datasheet to start to calculate your windings. Have a search on E-Bay for ETD Core and you will see what I mean.
It is important to buy one that you can get the data for, you will notice that they come in a miriad of materials N27 for example.
A typical choice would be something like an ETD core. You then need the datasheet to start to calculate your windings. Have a search on E-Bay for ETD Core and you will see what I mean.
It is important to buy one that you can get the data for, you will notice that they come in a miriad of materials N27 for example.
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I think you'll find most of the answers to your questions here...http://www.diyaudio.com/forums/power-supplies/244729-sg3524-smps-help-needed.html
Just an idea...
If you must have equal rails at the output at what ever load condition.
Make it with 24v isolated output.
If high regulation is not needed, dont regulate (no feedback).
Then divide the 24V output to +/-12V with an active virtual ground (this forces the two rails equal).
And simplifies output filtering...
For example: Look at IR2153... Make that push-pull (dont bootstrap it), very simple, very reliable...
If you must have equal rails at the output at what ever load condition.
Make it with 24v isolated output.
If high regulation is not needed, dont regulate (no feedback).
Then divide the 24V output to +/-12V with an active virtual ground (this forces the two rails equal).
And simplifies output filtering...
For example: Look at IR2153... Make that push-pull (dont bootstrap it), very simple, very reliable...
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