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DPA 426R switch

Posted by: SUSHIL on

          Dear sir,

 

                  We are using DPA 426R switch for 60 W , in which we are getting two output one +5v /8A and other 40v/ 200mA . Now the issue is , the dpa switch start s only when we remove the 40 v winding diode otherwise not .if we remove the 40v diode the switch starts normaly and frequency is 400khz  but 5v drop on load even after more than 1A. Pls do needful.

Comments

Submitted by PI-Neela on 07/12/2012

I assume you are sensing from the 5V channel not 40V channel. If that is the case, what is the Cpin cap you are using? That capacitance is critical for the operation. If you choose Cpin cap following our datasheet, then I need to look at your layout and schematic. 

Submitted by SUSHIL on 07/15/2012

Pls help us as schemetic is attached

Submitted by PI-Neela on 07/20/2012

One of the possibilities is that if the transformer winding connection is sohow swapped, accidently falyback becomes forward, there is a high current spike at turning on time, then that initical high current could trigger Iocp and even shut down the device for over temp protection. So maybe you could check if there is any mis connection for your transformer. If problem still presents, let us know.

Dear Neela ,

 The DPA does not shut down ,output comes continue but the voltage drop 5.3 V to 4.4V.

Submitted by PI-Neela on 07/24/2012

Under what condictions you see this Vo drop? it is start up transient or from light load to full load tansition?

However there are a few things u can improve from you current schematic:

1. C pin decoupling cap CP55 can be increased to 220nF

2. CP25 can be increased from 1uF to 4.7uF

3. you feed back resistor better be 1% resistor for better tolances.

Try these things to see if it helps.

Submitted by SUSHIL on 09/03/2012

Dear Neela,

                          Its Vo starts up from ligth load to high load transition. it dropps to all voltage after 2A. I have tried everything as per you.and transformer design is also working in old design but the problem is not yet resolved . Pls suggest what can i do further .

Submitted by PI-Neela on 09/04/2012

I wonder did you design your system using our PI Expert? If you already did, could you share with us your design file?  If you didn't, I suggest you to start a design, you can compare PI expert design with your current schematic, and also share with us. That will help us to resolve your problem.

link is http://www.powerint.com/en/design-support/pi-expert-design-software