Hello all,
We are looking to use the UCC28740 without an optocoupler for reliability reasons. We have considered UCC28710 but had too many problems with the sense pin that we decided to try the UCC28740 instead.
We are using the schematic from UCC28740EVM as a starting point, but with the following modifications:
1) since we are eliminating the opto, we are using the aux winding (BIAS) as main regulation source. We know regulation is not going to be good, but we use this to power relays, so we don't need accurate regulation. +/-10% is OK. Looking at the EVM sch we are connecting R21 and R15 to the VDD pin 1 of U1.
2) We are replacing the opto U2 with a PNP with E connected to opto emitter and C to opto collector. Base is driven cathode of TL431 (U3) through a base res. We are adding an emitter resistor to control gain.
3) We are planning on using the same compensation network to stabilize the feedback network.
We looked at the datasheet and the design guide is centered around opto usage. Does anyone have experience on this IC without an opto? Any feedback on this will be greatly appreciated!