I am building a SMPS circuit from a switching IC. This IC has feedback and enable pins for timing and current calculations respectively.
Transformer Data: (10 pin 1-5, 6-10)
primary: 1-3 – 60 turns, 3-2 25 turns (1-2 is total coil with 1.5 mH)
secondary: 6-10 – 7 turns
aux: 4-5 – 21 turns
When this circuit is operated in open mode (without load), it gives 5.2V (which is what i need). But when we start connecting load, voltage drops a little up to around 4.8V for some 1.4 A or 1.5 A need (10 ohm 10 W resisters in parallel to make load). If i take total parallel load up to 2.5 ohm, it should ideally give 2A at 5V. But happens is voltage start decreasing to 3 V as current raises to 2 A.
Why is that?
(I have tried using 2 1R0 or 2R2 instead of 2 1R5 for cs/enable but with no result, Also using 10 ohm in feedback after diode instead of 1 ohm)
IC: CT5503s
EDIT: Updated circuit Image
Best Answer
You have the output (secondary) of the transformer's phase reversed.