EDN Magazine — 04.13.95 Finding the keys to flyback power supplies produces efficient design (figure)

FIGURE 2

(A)	CH1 CH2 RF1 RF2	20V 10 mV 200V 10.0 mV	2 µSEC 2 µSEC	2 µSEC-8.27V EXT1

MOSFET DRAIN VOLTAGE 200 VDC/DIV
RF1gnd
PRIMARY TRANSFORMER CURRENT 500mA/DIV
RF2gnd
CH1gnd
DIODE (D2) VOLTAGE 2.0 V/DIV
SECONDARY TRANSFORMER CURRENT 5.0 A/DIV
CH2gnd

(B)	CH1 CH2 RF1 RF2	20V 10 mV 200V 10.0 mV	2 µSEC 2 µSEC	2 µSEC 1.09V EXT1

MOSFET DRAIN VOLTAGE 200 V/DIV
RF1gnd
PRIMARY TRANSFORMER CURRENT 500mA/DIV
RF2gnd
CH1gnd
DIODE (D2) VOLTAGE 2.0 V/DIV
SECONDARY TRANSFORMER CURRENT 5.0 A/DIV
CH2gnd

Fig 2—The voltage and current waveforms in (a) are representative of discontinuous operation, which results in low primary inductance. Triangular-current waveforms characterize discontinuous operation, where stored energy is completely delivered to the load. The voltage and current waveforms in (b) are representative of continuous operation, which results in high primary inductance. The secondary current is still flowing when the MOSFET turns on at the beginning of the next cycle, so stored energy isn't completely delivered to the load.