visions_of_eden
Newbie level 5
Hi , this is the sleep/wake-up circuit from a laser printer psu.
I don't understand the design . Why use 3 transistors to just reverse a signal (from active negative to active positive ) and not just apply SLP_N signal to the last transistor .
the only reason i could find is because if there's a failure on +5V rail it automatically shut down the PSU .
+3.3V line is always active , while +5V line is activated only when PSU is not in sleep mode (SLP_N positive or +5V active in this design ) .
Can anybody help me understand this design ? Thanks .
I don't understand the design . Why use 3 transistors to just reverse a signal (from active negative to active positive ) and not just apply SLP_N signal to the last transistor .
the only reason i could find is because if there's a failure on +5V rail it automatically shut down the PSU .
+3.3V line is always active , while +5V line is activated only when PSU is not in sleep mode (SLP_N positive or +5V active in this design ) .
Can anybody help me understand this design ? Thanks .