Here are some 3V to 9V DC boost converter circuits that were requested by some of our visitors. It may be helpful to have one of this converters when no 9V battery is available or if you consider that they are too expensive. The first circuit is very simple, it uses the TL496 power supply controller, a coil and a electrolytic capacitor.
The maximum output voltage is actually 8.6V and current is around 80mA.
The input current (the current drawn from the batteries) is 405mA at the maximum output current. Without load the current consumption is 125µA and the batteries life is around 166 days.
Probably there are more 3 to 9 volt dc converters but for the moment those are the only ones presented in this article.