When a control IC is employed it's quite easy to ensure proper switching even at no load, just place a resistor between the center tap of the control side of the pulse transformer and +Vcc to induce an auxiliary base current.
See AT and ATX power supply schematics, most of them use this approach, you will see also a diode in series with that resistor to prevent it from stealing base current
See AT and ATX power supply schematics, most of them use this approach, you will see also a diode in series with that resistor to prevent it from stealing base current
