2019-05-09 A 3V to 9VDC Boost Converter V. 1.1

I built this in 2007. No load it puts out 9.5VDC and at 22 mA it puts out 8.5VDC. It works okay for powering a radio on the FM band, but it has too much RF Interference on the AM band. The original circuit had only a single output transistor but it couldn’t handle enough current so I added the little PCB with four BC338 transistors in parallel. I extended the wires for the coil so I could experiment with different toroid coils. The one in this photo is two FT37-43 cores stacked, with about 18 turns of 26 AWG wire, measuring 250 microhenrys. The black and white output wires are wound around a RFI suppressor sleeve before exiting the case, but this is not enough to remove the RFI. There need to be more chokes outside to reject the RF interference before the radio will be able to pick up stations. I added those filters and the radio receives the AM stations with a slight amount of hash between stations.

Some call this a Joule Thief circuit, but it does not have a second winding on the coil so


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