On Tue, May 3, 2022 at 03:59 PM, lpb612 wrote:
On Tue, May 3, 2022 at 03:58 PM, lpb612 wrote:
There is no DC feedback in the error amplifier TL494/U2. Just R1033 in
series
with C1033. The same happens with U4 - no feedback at all. Therefore the
output voltage V2 and V4 should be either LOW or HIGH, but not in the
middle,
as Figure 3-11 seem to suggest. It can work like this in a bang-bang way
(100%
or 0% duty cycle). But is this how the circuit is supposed to work?
Correction of typo: V2 and V4 should be U2 and U4, the error amplifiers.
---
That is what I guessed in my reply. U4 is wired for over voltage protection so it is OK it be be on/off. When over voltage at the primary happens it needs to turn off the switcher.
U2 is the one that controls the loop. As I wrote in the previous message it is wired more like an integrator, it also has a zero coming from R1033 for compensating the loop, so in normal operation output of U2 is a control voltage and not on/off only. There is no local DC feedback between pins 2 and 3 but global feedback (around the full switcher control loop) still controls DC voltage at the input.
Ozan
