Electronics > Projects, Designs, and Technical Stuff
What is this circuit doing?
(1/1)
elimenohpee:
I developing an application where I need to current share a couple of external, stand-alone DC switch mode power supplies. I'm planning to use TI UC2907 as a load share controller. There aren't any application notes specifically on this chip, but there is a note on UC3907 with an approach that I want to use. It looks like it ties into the sense feedback lines to drive/share the current between the supplies.
In the application note it shows a rough schematic of the approach (see the attached image), but I'm a little confused what the highlighted portion is doing. It looks like it's clamping the emitter of the transistor at the chip's reference voltage but I don't really understand why. Does anyone have any idea what this portion of the circuit is doing?
Mr Evil:
From looking at the block diagram in the datasheet, pin 8 is a 1.75V reference voltage, so it will pull up the emitter of the transistor by a few hundred millivolts, preventing it from pulling down on the power supply's sense line until the output from the adjust amplifier rises above a threshold. Without spending too much time trying to work it out, it seems that this is because the output from the adjust amplifier is >0V under quiescent conditions, so R3 prevents it from constantly trying to adjust the power supply's output even when there is no current output from it.
Navigation
[0] Message Index
Go to full version