A start up circuit for power converters is presented. It includes a JFET transistor, a resistive device, a first transistor, a second transistor and a diode. The JFET transistor is coupled to a voltage source. The first transistor is connected in serial with the JFET transistor to output a supply voltage to a control circuit of the power converter. The diode is connected from a transformer winding of the power converter to supply a further supply voltage to the control circuit of the power converter. The second transistor is coupled to control the first transistor and the JFET transistor in response to a control signal. The resistive device provides a bias voltage to turn on the JFET transistor and the first transistor when the second transistor is turned off. Once the second transistor is turned on, the first transistor is turned off and the JFET transistor is negative biased.