Hi I'm trying to build a circuit that will multiply the input voltage by a factor of 5.

Here is what I came up with:

When I use a PWM signal of 0.5 ON, the output is about double the input so it works fine, but when I change to 0.8 PWM ON, the output doesn't change much (increased by 0.2V).

Any of you have suggestions?

 

Hi Dan,
Welcome to AAC.
Try a lower value for the inductor.
This is one option.
E

 

If you don't already have it, add something like a resistor to limit the base current. This probably won't fix your problem with limited voltage range but it might save you grief from complications.

Also, make sure the DC resistance of your inductor is much lower than your load.

 

Hi Dan,
Welcome to AAC.
Try a lower value for the inductor.
This is one option.
E

Thank you for answering,
I replaced the inductor with 47mH and the Vout dropped to 1.2V (was 2.3V with 100mH).

 

If you don't already have it, add something like a resistor to limit the base current. This probably won't fix your problem with limited voltage range but it might save you grief from complications.

Also, make sure the DC resistance of your inductor is much lower than your load.

There is a base current limit resistor of 470 ohm (not in the diagram)
DCR = 20 ohm

 

470 millihenry? I missed that the first schematic showed 100 mH.

Most likely your inductance and resistance are too high.

For a frequency of tens of kilohertz being well below 100 microhenries is common for many applications.

 

hi Dan
What is the DC resistance of the Inductor.?
E

 

Hello,

Perhaps the 1N4448 is not suitable.
Eric used a UF4007 in his simulation.

Bertus

 

hi Dan
What is the DC resistance of the Inductor.?
E

I have no datasheet but by measuring its 20 ohms for 2 47mH in series

 

470 millihenry? I missed that the first schematic showed 100 mH.

Most likely your inductance and resistance are too high.

For a frequency of tens of kilohertz being well below 100 microhenries is common for many applications.

Can you please show a formula for that so I can better understand?

 

hi Dan,
This what I get, comparing one and two inductors,
Using a Schottky diode == to 1N4448
E

EDIT:
I assume this 0.5 means 50% duty cycle.?

 

Hello,

Have a look at the attached PDF's.

Bertus