Voltage regulator feedback

rail of approx 5.3V (unregulated is fine). Due to space and cost we cannot add another regulator for 5.3V or us dual regulators. So I added a schottky diode D2 as shown in the schematic below and taken the feedback to the regulator after D2. The 2 feedback resistors R2 and R3 values are unchanged from the existing design of 5V. If 5V is maintained after D2 there will be approx 5.3V before D2 (due to diode drop). Does this work? Are there any shortcomings with this approach?

Different propagation times for up and down transients? Just a guess, really.

ther rail of approx 5.3V (unregulated is fine). Due to space and cost we ca nnot add another regulator for 5.3V or us dual regulators. So I added a sch ottky diode D2 as shown in the schematic below and taken the feedback to th e regulator after D2. The 2 feedback resistors R2 and R3 values are unchang ed from the existing design of 5V. If 5V is maintained after D2 there will be approx 5.3V before D2 (due to diode drop). Does this work? Are there any shortcomings with this approach?

I don't know much about switching supplies. But if you had to sink current into the 5V supply that might be an issue. (I might add a bit of capacitance to the 5 V supply.)

George H.

nother rail of approx 5.3V (unregulated is fine). Due to space and cost we cannot add another regulator for 5.3V or us dual regulators. So I added a s chottky diode D2 as shown in the schematic below and taken the feedback to the regulator after D2. The 2 feedback resistors R2 and R3 values are uncha nged from the existing design of 5V. If 5V is maintained after D2 there wil l be approx 5.3V before D2 (due to diode drop). Does this work? Are there a ny shortcomings with this approach?

It should be ok, but the 5.3V wont be accurate in any way. The drop will va ry according to temperature, current and initial tolerances.

Cheers

Klaus

ther rail of approx 5.3V (unregulated is fine). Due to space and cost we ca nnot add another regulator for 5.3V or us dual regulators. So I added a sch ottky diode D2 as shown in the schematic below and taken the feedback to th e regulator after D2. The 2 feedback resistors R2 and R3 values are unchang ed from the existing design of 5V. If 5V is maintained after D2 there will be approx 5.3V before D2 (due to diode drop). Does this work? Are there any shortcomings with this approach?

No problems if you use appropriate Schottky, something like the Vishay SB52

nother rail of approx 5.3V (unregulated is fine). Due to space and cost we cannot add another regulator for 5.3V or us dual regulators. So I added a s chottky diode D2 as shown in the schematic below and taken the feedback to the regulator after D2. The 2 feedback resistors R2 and R3 values are uncha nged from the existing design of 5V. If 5V is maintained after D2 there wil l be approx 5.3V before D2 (due to diode drop). Does this work? Are there a ny shortcomings with this approach?

is negligble, probably lower than that of C6 so it does not require additi onal decoupling. You must add the 5.3V loading to the 5V loading on the LM2

Thanks all. I will rework the board and test once.

-mj