How to make a slow boot power ?

[shalky]

I need a power circuit: input voltage +9v, output voltage +5v, current 200ma. Some components require the voltage raises slowly when the power starts. Is there anyone has such experiences ?

 

[VVV]

You are describing a regulator with so-called soft-start. You can impement it by adding a capacitor (RC filter, plus a diode) on the reference input of the error amplifier. That way, at power up the reference voltage rises slowly and so does the output voltage.
For switching regulators, a similar method can be used, although it is more common to directly foce the duty-cycle to increase slowly to the final value.

Do you have a preference for the actual circuit? A linear one would dissipate about 4V*200mA=800mW. Is this acceptable?

 

[IanP]

Take a look at the picture below .. for 5V output R1≈720Ω, R2=240Ω ..
For more details goto:
**broken link removed**
Regards,
IanP

 

[shalky]

Many thanks to VVV!

There is no reference in my circuit, but I refer your idea and design a control signal to let the power to soft-start.

Give you a helped me!

Thank you very much !