Wide range DC-DC 5.7:1

Posted by: Little Bear on 07/14/2016

I see a reference design for InnoSwitch-EP Family for 85-484 VAC. This is a ratio of 5.7 to one. I need to design a 10 watt DC-DC that covers an input range of 21 to 120 Vdc. The sofware only reports errors like input voltage too low and exeeds duty cycle. Do you have any parts that will work for this design?

Comments

Hi Little Bear,

Thank you for choosing Power Integrations.

May I know what application will you be using the power supply for?

We have TOPSwitchJX which could start up with a drain voltage of 18VDC.

Tinyswitch-4 is another device that you could use. It has a minimum drain supply voltage of 50V but by using a floating constant current source supplying the BYPASS (BP) Pin, the device could be made to start at even lower input voltages. Here is a link to the circuit idea.

https://ac-dc.power.com/design-support/circuit-ideas/floating-constant-current-source-allows-ultra-wide-input-voltage/

Regardless of which device you eventually choose you have to make sure that your input and output electrolytic capacitors follow the recommended capacitance to maintain regulation even at full load. You must also take note that since you are designing a 10W PSU that your transformer is correctly designed with power dissipation taken into account.

Hope this helps.

I tried the PI Expert software selecting the TOPSwitchJX and it gives an error stating the min is 36 volts and the duty cycle exceeds the device limit

I am intrested in the INNOSwitch for the syn rectifiers. My supply outputs are isolated +/- 24V 0.18A and 5V 0.07A.

Will the syn rectifiers be more efficient at these low currents and can I get better cross regulation?

You would need to design with a low reflected voltage for this to work. Probably less than 50V. If you can send your PIexpert file, I could help you check and advise what can be done to meet your requirements.

What is your efficiency specification? Definitely, efficiency with the synchronous rectifiers will be higher. However the minimum drain supply voltage for Innoswitch is only 50V.

Cross regulation will generally depend on your feedback and/or your transformer winding coupling. However, having synchronous rectifiers will remove variation caused by the output diode forward voltage.