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18W offline flyback with large secondary capacitor.

We are currently looking to design a 18W offline flyback as follows:-

 

Currently I have done the design  and have chosen to use UCC28C40D , and another design with UC3843.

-However, my boss believes the component count is too high and says we need a different solution.

-Please can I speak with Texas staff  about our requirements?

 

 

Spec:

Vin = 85-265VAC

 

Vout1 = 36V     +/-2V;            13W

Vout2 = 5V,      +/-0.25V;         4W

Vout3 = 3.1V,   +/- 0.3V;         0.6W

 

(Vout1,2,3 are fully SELV isolated outputs….not isolated from each other though)

 

Efficiency = 85%

 

Standby Power =  <500Mw.

Frequency = 50-150KHz.

 

Skip-cycle during light load.

 

Capacitance on 36V Rail = 30mF.

(…..this is for energy storage for when there is a mains power cut when the customer is  running  fluid from the tanks….it  closes the  fluid flow off with the stepper motor valves)

-this 30mF  capacitance should  be charged up in  ~ 1 second after power_ON……but we may allow this to extend up to say 3 seconds.

 

 

 

 

 

 

 

 

 

Notes on Standby:-

Our standby requirement is interesting, because during standby, our 5V & 3.1V  rail is actually loaded with 170mW……..

….-this is due to the RF transceiver, which must keep listening for an ON command from the remote   device during standby.)

 

High  energy storage capacitance:

Most PWM controllers go into hiccup mode when  charging up our big secondary capacitance. –and so are not useful to us

 

 

Anyway,  myself and the R&D Engineering Manager, were wondering if you may have any suggestions to suit our requirement?

 

Schematic:

http://i52.tinypic.com/ab1ibt.jpg

 

……..please note that LT1243  is pin for pin compatible with our intended device, (UCC28C40D) from Texas

 

Here is the simulation file in LTSpice:-

http://www.2shared.com/file/zNwuM_u5/Matalan_SMPS_simulation__1_7__.html

 my phone number is UK 07798 851534