Hello dear Alice, looking for a small step up conversion circuit?
What are you trying to power up?
What is the input and output Voltage x Current?
:)

Wagner.


Example of a simple circuit:
                                 Diode
                            .------>|------------o---o  High V
                            |                    |
                            3| <- point A        |
                            3|                  --- HV C
                            3|                  ---
                            3|                   |
+1.5V----o------------------3| <- point B        |
         |                  3|                  GND
         R                  3|
         |      Nc----------3| <- point C
         o------P           3|
         |      Ne--.       3|
         |          |       3| <- point D
         |         GND       |
         |                   |
         '---------||--------'
                   C

This circuit use a "one coil" transformer with two taps.

At power on, all points have the same +1.5V.

 1) Resistor R makes the NPN transistor conducts

 2) Current Flows from ground to point C, via coil to B to +1.5Vdc.

 3) Point C is grounded

 4) Point D will develop a voltage below ground

 5) Point A will develop a voltage higher than +1.5V.

 6) Voltages goes increasing

 7) Voltage at point D is enough negative to cut off transistor
    via capacitor C.

8)  Transistor opens, Point C goes floating.

9)  High + Voltage at Point A is rectified and stored at HV C.

10) Capacitor C (blocking the transistor) starts to discharge via R
    and coil taps D-B.

11) Upon C discharged, R is enough to turn on transistor again.

Cycle repeats in a frequency determined by R, C, and the transformer
itself.

This kind of configuration was widely used, using a cheap small
transistor audio output transformer (transistor radio), connecting the
secondary in series with the primary.  Some different configuration was
used at those toys to catch your friends with 500Vac from a single
cell... remember?  Nasty salty taste of high V... :)

!!! Watch out kids, don't do it at home, you can kill the cat !!!