Hello again,
I'm in the process of putting together a "UV exposer" with a MAX1698A led driver, and i've decided to supply it from a 5vsb section "grafted" from an HP power supply, based on a TNY266 chip.
The schematic i'm using is attached below. Now, the switcher is definitely working (scoped it out), and on the 220u filter cap, from the aux primary winding, i'm getting 14-17v. Trouble is, for some reason, the chip is on minimum duty cycle, and on the secondary, i'm getting some tiny blips (which i'm not even sure are enough to open the rectifier schottky). I also changed the optocoupler, same thing.
I wonder if the coil i'm using is a bit too big (180uH), but... Should / could that affect things quite like that? Secondary caps are two 1500uH/6.3v Nichicon HD. I also tacked on a 51ohm resistor as a ~100mA minimum load. Nothing else is mounted on the board (so just supply-related components).
Could the TL431 be bad?
I'm in the process of putting together a "UV exposer" with a MAX1698A led driver, and i've decided to supply it from a 5vsb section "grafted" from an HP power supply, based on a TNY266 chip.
The schematic i'm using is attached below. Now, the switcher is definitely working (scoped it out), and on the 220u filter cap, from the aux primary winding, i'm getting 14-17v. Trouble is, for some reason, the chip is on minimum duty cycle, and on the secondary, i'm getting some tiny blips (which i'm not even sure are enough to open the rectifier schottky). I also changed the optocoupler, same thing.
I wonder if the coil i'm using is a bit too big (180uH), but... Should / could that affect things quite like that? Secondary caps are two 1500uH/6.3v Nichicon HD. I also tacked on a 51ohm resistor as a ~100mA minimum load. Nothing else is mounted on the board (so just supply-related components).
Could the TL431 be bad?
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