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50 Watt constant power supply design using FL7733A

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nilayshah812

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i have designed constant power supply using fairchild's fl7733a ic
Specifications
I/p voltage : 80 - 280V
Output Voltage : 7-40 v
Output current : 1.5Amps

When i connect full load led lights flicker when voltage is low(around 80 v ) but as soon as voltage is increased lights work properly. what must be the cause?
 

Hi,

You sent a riddle. Without schematic, without device values, without any useful information.

My assumption: transformer saturation.

If you need more help it is urgent to post your schematic and all informations about the used devices.

Klaus
 



i Have uploaded the schematic
transformer design

Primary Turns 37
Secondary Turns 18
Aux Turns 7
 

Some possibilities:

-Under voltage lockout feature
-Primary switch overcurrent limit
-Transformer saturation
 

your current snese resistors are not sized to allow proper peak current?

- - - Updated - - -

R1, R2, R3 are 10k, 15k, 15k...seems very low for a startup branch.
 

In their application note they have used the same value resistors. I increased the value of r1 to 1M it only delayed the startup time but flickering was still there. How we know if transformer is saturating or not. As the voltage reaches 130V the power supply is working fine.
 

Hi,

How we know if transformer is saturating or not.
Click to expand...
Use a scope to show the primary current wavform.

Klaus
 

I checked that yes the transformer was saturating so i made a new transformer and it is working fine but the new problem is it heats up to 80deg and also power factor reduces as the input voltage increases (Pf 0.94 for 230v). where to look for the problem According to datasheet capacitor at comi pin should be increased. I increased it from 2.2uf to 4.7uf but the power factor only increased by 0.01
 

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