Voltage Control for Power Supply

[OKiDOKI]

Hallo ,
i have a little Korg Monotron Delay that operates with 3 volt @ 90mA. The idea is to add a potentiometer that controlls the Vc from 1 Volt to 3 Volt.
The power source is 3.6 Volt from my microcontroller.
Doing this i can make some more noise sound modulation. The goals is to calculate the resistor value of the potentiometer based on a voltage divider concept.

At the end I got this numbers: 3.6V|---------R1 = 6.6 Ω ------- Rv = 22 Ω ------- R2 =11 Ω.---------| 0V

The problem is right now, I can`t find a potentiometer that has a 22 Ω value to control the range from 1 volt to 3 volt at 90mA.

If i use a Rv = 10K the current draw falls to 200μA.
And this would not have enough power if my synth works at 90mA. ????

 

[Honduras]

Hallo ,
i have a little Korg Monotron Delay that operates with 3 volt @ 90mA. The idea is to add a potentiometer that controlls the Vc from 1 Volt to 3 Volt.
The power source is 3.6 Volt from my microcontroller.
Doing this i can make some more noise sound modulation. The goals is to calculate the resistor value of the potentiometer based on a voltage divider concept.

At the end I got this numbers: 3.6V|---------R1 = 6.6 Ω ------- Rv = 22 Ω ------- R2 =11 Ω.---------| 0V

The problem is right now, I can`t find a potentiometer that has a 22 Ω value to control the range from 1 volt to 3 volt at 90mA.

If i use a Rv = 10K the current draw falls to 200μA.
And this would not have enough power if my synth works at 90mA. ????

First off, I've just pent about a month looking at low voltage/low current sources. I wish you luck.

One idea that I saw was to use an LM7803 with the Vr between the sense pin and ground. I haven't tried it, and you would probably have to use a current limiter with it. There are a few schematics for low current limiters using 2-4 BJTs, but I've never looked at them too hard. The version of the LM7803 that is in the small package may have a built in 0.1 Amp limit, but I'm not sure.

The Texas Instruments datasheet PDF for the LM78XX series might give you some useful ideas.

It's like I said. Not too many people seem to be working in this range.

 

[MikeMl]

Please post a schematic diagram. The part about 3.6V from a microcontroller makes no sense...

 

[alec_t]

The idea is to add a potentiometer that controlls the Vc from 1 Volt to 3 Volt.

I very much doubt the Monotron Delay will operate with less than 3V as its supply. It's a microprocessor-based device.

 

[OKiDOKI]

Hi ...

I very much doubt the Monotron Delay will operate with less than 3V as its supply. It's a microprocessor-based device.

It will make some noise glitch-sound at 1Volt ...., based on the schematics its complete an analog device without a microcontroller inside.

Please post a schematic diagram. The part about 3.6V from a microcontroller makes no sense...

I did at the bottom... 3,3 Volt should come from the microcontroller but i measure an output of 3.6 Volt... ???

 

[alec_t]

It will make some noise sound..

Have you actually tried it with, say, a 1.2V or 1.5V supply from a single AA cell (NiMH or alkaline)?

 

[OKiDOKI]

Have you actually tried it with, say, a 1.2V or 1.5V supply from a single AA cell (NiMH or alkaline)?

I got this Info from this blog https://amazingdiy.wordpress.com/2012/03/18/monotron-delay/

"Doing a few tests with lab PSU, my Delay seems to draw between 0.27W when in use. Thus with a input voltage of 3 volts, the current draw is around 90mA. The synth starts introducing a mildly audible tremolo effect over the output when input voltage drops around 2.5V. I assume it’s the LFO LED turning on that makes the internal operating voltage duck, in turn causing a dip in the overall volume.. At least the tremolo is firmly tied to LFO speed . From here, going down to below 2V starts causing other random behaviour, like pitch warbling on high tones, and the synth dies entirely when input voltage hits 1V. Tampering with operating voltage is of course one of the easy circuit-bending tricks, if random behaviour is what you’re after "

Using a potentiometer i could do these effects...

 

[alec_t]

based on the schematics its complete an analog device without a microcontroller inside.

Ok. My bad. Can you post a link to its schematic?

 

[OKiDOKI]

Ok. My bad. Can you post a link to its schematic?

https://amazingdiy.files.wordpress.com/2012/03/md-schematic.jpg

 

[OKiDOKI]

Ok. My bad. Can you post a link to its schematic?

https://amazingdiy.files.wordpress.com/2012/03/md-schematic.jpg

 

[Honduras]

Take a look at Figure 27.

https://www.ti.com/lit/ds/symlink/lm317l-n.pdf

There are also a number of current limiters shown including precision variable, for the same device.

 

[alec_t]

Here's a simple circuit you could try. It's somewhat dependent on the gain (beta) of the transistor, but may be ok for your purpose. Transistor type isn't critical, as long as it's an NPN with reasonable gain and a current rating >= 200mA.

 

[OKiDOKI]

Probably I find the solution on this blog:
LM317T Variable Voltage Regulator
**broken link removed**

 

[OKiDOKI]

Here's a simple circuit you could try. It's somewhat dependent on the gain (beta) of the transistor, but may be ok for your purpose. Transistor type isn't critical, as long as it's an NPN with reasonable gain and a current rating >= 200mA.View attachment 90679

Hi thanks for this schematics!!!!
I will try it .... seems simple---

 

[Honduras]

Probably I find the solution on this blog:
LM317T Variable Voltage Regulator
**broken link removed**

Did you look at the 0 vdc - 30 vdc regulator? I thought that might be a little closer to what you need.

 

[Honduras]

What Alec is suggesting looks a lot simpler than my idea.