Simplified primary triggering circuit for the switch in a switched-mode power supply

Trigger circuit for a switch in a primary-side, triggered switching power supply, the trigger circuit comprising:

• a supply voltage terminal for supplying the trigger circuit (200, 400) with a supply voltage,
• a control terminal for the output of a trigger signal from the trigger circuit for supply to a control input of the switch,
• a ground terminal for connecting the trigger circuit to a ground potential, and
• a peak current detection terminal for detecting a primary-side peak current,
• wherein the trigger circuit is configured to receive a feedback signal at the peak current detection terminal, the feedback signal being representative of an auxiliary voltage that is induced on an auxiliary winding (L4) of a transformer of the switching power supply, and wherein the feedback signal is superimposed on the voltage at the peak current detection terminal.

Primary-side, triggered switching power supply comprising:

• a transformer with a primary-side main winding and a secondary-side main winding, wherein electrical energy pulses are transmitted from the primary-side main winding to the secondary-side main winding,
• a primary-side switch for turning on and off a primary current through the primary-side main winding in response to a trigger signal,
• an auxiliary winding in which a voltage pulse is induced after the primary-side switch is turned off, and
• a primary-side trigger circuit comprising:
• a supply voltage terminal for supplying the trigger circuit with a supply voltage,
• a control terminal for the output of the trigger signal from the trigger circuit for supply to a control input of the primary-side switch, and
• a ground terminal for connecting the trigger circuit to a ground potential,
• wherein the trigger circuit is configured to receive a feedback signal at the supply voltage terminal, the feedback signal being representative of the voltage pulse that is induced on the auxiliary winding, and wherein the feedback signal is superimposed on the supply voltage.

Primary-side, triggered switching power supply comprising:

• a transformer with a primary-side main winding and a secondary-side (L3) main winding, wherein electrical energy pulses are transmitted from the primary-side main winding to the secondary-side main winding,
• a primary-side switch for turning on and off a primary current through the primary-side main winding in response to a trigger signal,
• an auxiliary winding in which a voltage pulse is induced after the primary-side switch is turned off, and
• a primary-side trigger circuit comprising:
• a supply voltage terminal for supplying the trigger circuit with a supply voltage,
• a control terminal for the output of the trigger signal from the trigger circuit for supply to a control input of the primary-side switch,
• a ground terminal for connecting the trigger circuit to a ground potential, and
• a peak current detection terminal for detecting a primary-side peak current,
• wherein the trigger circuit is configured to receive a feedback signal at the peak current detection terminal, the feedback signal being representative of the voltage pulse that is induced on the auxiliary winding, and wherein the feedback signal is superimposed on the voltage at the peak current detection terminal.