A power supply circuit comprising a first conversion stage and one or more second conversion stages; the first conversion stage comprising: input terminals for connection to an ac or dc supply; an electronic converter with controlled or pre-determined output current characteristics; and first and second output terminals for connection to the one or more second conversion stages; each of the one or more second conversion stages comprising: input terminals to receive a substantially constant current input from the first conversion stage; a current multiplier circuit; and output terminals for connection to a load; characterised in that the electronic converter of the first conversion stage is a high frequency series parallel resonant converter, with an inductance connected in series with a capacitor; in that the first and second output terminals are connected across the capacitor or the inductance, whereby the mid-point of said inductance and said capacitor is connected to said first output terminal; in that, for at least one of the one or more second stage converters, if the first and second output terminals are connected across the capacitor in the first stage, then a second inductance (131,231) is connected in the second stage converter between the first output terminal of the first converter stage and the current multiplier circuit of the second converter stage; and in that, for at least one of the one or more second stage converters, if the first and second output terminals are connected across the inductance in the first stage, then a second capacitor is connected in the second stage converter between the first output terminal of the first converter and the current multiplier circuit of the second converter stage. input terminals for connection to an ac or dc supply; an electronic converter with controlled or pre-determined output current characteristics; and first and second output terminals for connection to the one or more second conversion stages; each of the one or more second conversion stages comprising: input terminals to receive a substantially constant current input from the first conversion stage; a current multiplier circuit; and output terminals for connection to a load; characterised in that the electronic converter of the first conversion stage is a high frequency series parallel resonant converter, with an inductance connected in series with a capacitor; in that the first and second output terminals are connected across the capacitor or the inductance, whereby the mid-point of said inductance and said capacitor is connected to said first output terminal; in that, for at least one of the one or more second stage converters, if the first and second output terminals are connected across the capacitor in the first stage, then a second inductance (131,231) is connected in the second stage converter between the first output terminal of the first converter stage and the current multiplier circuit of the second converter stage; and in that, for at least one of the one or more second stage converters, if the first and second output terminals are connected across the inductance in the first stage, then a second capacitor is connected in the second stage converter between the first output terminal of the first converter and the current multiplier circuit of the second converter stage. input terminals to receive a substantially constant current input from the first conversion stage; a current multiplier circuit; and output terminals for connection to a load; characterised in that the electronic converter of the first conversion stage is a high frequency series parallel resonant converter, with an inductance connected in series with a capacitor; in that the first and second output terminals are connected across the capacitor or the inductance, whereby the mid-point of said inductance and said capacitor is connected to said first output terminal; in that, for at least one of the one or more second stage converters, if the first and second output terminals are connected across the capacitor in the first stage, then a second inductance (131,231) is connected in the second stage converter between the first output terminal of the first converter stage and the current multiplier circuit of the second converter stage; and in that, for at least one of the one or more second stage converters, if the first and second output terminals are connected across the inductance in the first stage, then a second capacitor is connected in the second stage converter between the first output terminal of the first converter and the current multiplier circuit of the second converter stage.