Need Flyback with two outputs and good cross regulation
Hi,
We wish to have an offline Flyback SMPS, 90-265VAC input.
Sometimes we wish it to give two outputs which are isolated from the input
by 3500VAC and isolated to 3500VAC from each other.
The two outputs are 24V, 2A and 20V, 2A.
But also, sometimes (and we can adjust the value of the output divider for this)
we need the outputs to be 24V, 2A and 15V, 3A and these are isolated from the mains input
but don't need isolation from each other.
So this is with one single transformer, that could sometimes be used in a product with
24V, 2A and 20V 2A outputs, and sometimes in a product where it would need to give 24V,2A and 15V, 3A outputs.
What could you suggest for this?, and what kind of cross regulation could we expect?
Consider that either output could be on full load when the other is on no load.
____
Also, please could you advise on all DER and RDK reports concerning your dual output flybacks where both of the outputs are >20W?
Comments
If you are using two outputs with separate grounds, expect to need to play games with resistive preloading to get regulation. Don't expect regulation better than 10-15% for two outputs with separate grounds, though the output that actually has feedback should get decent regulation. Expect regulation issues if you widely vary the load on the output that has feedback, since the other output has no feedback to control it. You may have to put a heavy resistive preload on the output with feedback and linear regulate the second output that has no feedback connection.
What sort of load range are you expecting for the two outputs?
Hello treez,
For the device, given the power requirements, some devices you can use are the InnoSwitch3-EP and the TopSwitch-JX. Our InnoMux2 device would be best for good cross-regulation, multiple output designs but it is only for applications where the outputs do not need to be isolated from each other so it will not be applicable for one of your use cases.
For cross-regulation, the main output that has a direct connection to the feedback should be fine regardless of the loading condition, but the other output can vary greatly depending on things like the turns ratio and coupling between windings. Depending on your regulation tolerance requirements, a Zener or maybe a simple regulator may be necessary in order to achieve proper regulation in all cases.
Below are a couple of dual output DERs where the power of each individual output is relatively high. There are others but their power levels are much lower than what you require.
DER-544: https://www.power.com/design-support/design-examples/der-544-40-w-dual-output-power-supply
DER-571: https://www.power.com/design-support/design-examples/der-571-40-w-dual-output-power-supply
I will also link below the product page of our InnoMux2. There you can see many multiple output designs that you can use for reference but all of them have outputs that are not isolated from each other.
InnoMux2: https://www.power.com/products/innomux/innomux2-ep