[SOLVED] Help with power supply for a guitar effect

[slow_rider]

I'm trying to design a power supply for a guitar effect. It should work from a 12Vdc power supply as well as a 9V battery. The effect needs supply of 9Vdc, 5Vdc & 4.5Vdc.
The 9V & 4.5V are pretty low or current draw and 5V needed for digital part which draws about 100mA.

I would like to design a simple circuit that could output these voltages and while working with a battery will keep the 9V output for as long as possible. Probably using a switcher. My resources are pretty limited and I am using parts mostly from futurlec.com which carries switchers by national semi. At this point I have a linear regulator for 9V for wall adapter usage and a switcher regulator for 5V output that can take anything down to almost 5V. I need a solution for the 9v feed from battery and a solution for 4.5V supply. Thanks!

 

[BradtheRad]

Are all the feeds positive voltage, or are you using any of the feeds as a ground reference? In other words does your project have a negative supply rail?

5V needed for digital part which draws about 100mA.

Is this a TTL IC? Can you substitute a CMOS type? It draws less current and can use a range of supply voltages.

regulator for 5V output

If you have 5V then you can get a 4.4V feed by inserting an inline diode.

I need a solution for the 9v feed from battery

Do you mean you want to prevent current flowing backwards through the battery when you use the wall adapter? A diode is the simplest way but it will subtract .6V when you draw from the battery.

Suppose you were to use a rechargeable 9V (the 8.4V type containing 7 cells, not the 7.2V with 6 cells)? It could charge at 9V from the wall adapter. No intervening components will be necessary.

Each cell would be maintained at 1.28V which is about the same as its voltage on a shelf.

 

[slow_rider]

The digital circuitry is composed of an MCU and a digital pot. I have some logic ICs as well, all are CMOS. The reason I would like 5V is because I need to keep the clock speed is the MCU.
All the feeds are positive, I think I wasn't clear enough on this part... I can use the barrel jack's switch to disconnect the battery when a wall-wart plug is inserted. What I am worried about is the voltage drop the battery will have after being used for a while. I would like to use a switcher (boost) so it will keep on outputting 9V even when the battery is at 5V for example (although it won't be able to supply much current).

Are all the feeds positive voltage, or are you using any of the feeds as a ground reference? In other words does your project have a negative supply rail?



Is this a TTL IC? Can you substitute a CMOS type? It draws less current and can use a range of supply voltages.



If you have 5V then you can get a 4.4V feed by inserting an inline diode.



Do you mean you want to prevent current flowing backwards through the battery when you use the wall adapter? A diode is the simplest way but it will subtract .6V when you draw from the battery.

Suppose you were to use a rechargeable 9V (the 8.4V type containing 7 cells, not the 7.2V with 6 cells)? It could charge at 9V from the wall adapter. No intervening components will be necessary.

Each cell would be maintained at 1.28V which is about the same as its voltage on a shelf.

 

[BradtheRad]

Your idea can work, but a switcher will try to extract ever-increasing current from the declining battery in order to step it back up to 9V. When the cells are down to 1.1 V each (6.6V total), the battery is pretty much discharged.

Is it correct, you are drawing at least 1/2 W from a 9V battery? It's a lot for that size.

You may have to resort to using 7 or 8 individual cells. AAA maybe. It's awkward of course.