Space Saving Secondary Side Synchronous Rectification Controllers for Flyback Converters

8 May 2020 - 0 Comments

STMicroelectronics’ high efficiency, low power consumption SRK1000A and SRK1000B synchronous-rectification (SR) controllers for flyback converters are now available in a new affordable and small footprint. They are designed for fast turn-on with minimum delay, and with innovative adaptive turn-off logic, the devices maximize synchronous rectification MOSFET conduction time and minimize the effects of parasitic inductance in the circuit without the need to add external components, this will improve the system efficiency and reduce the bill of materials.

The SRK1000A and SRK1000B both can manage a wide range of flyback controllers including quasi-resonant (QR) and mixed CCM/DCM fixed frequency operation up to 300kHz and they both allow programmable blanking time after turn-on (TON), via resistor selection, to prevent noise from inducing spurious behavior.

Both the devices offer an efficient low power mode at light load to enter a low consumption sleep mode when synchronous rectification is not beneficial, the problem is handled by detecting primary-side controller burst-mode operation, or when the SR MOSFET conduction becomes lower than the programmed minimum TON. The smaller-footprint option makes these devices suitable for battery chargers, quick chargers, adapters, and USB power-delivery outlets.

Features of SRK1000A and SRK1000B

Wide Vcc operating voltage range 3.75 to 32 V
Drain Source Voltage: 100V
CC regulation operation down to 2 V output supported
The very low quiescent current in low consumption mode (160 μA)
Fixed blanking time after turn-off (TOFF) : 2μs(SRK1000A), 3μs(SRK1000B)
Operating frequency up to 300kHz
The output can sink up to 1A and source up to 0.6A to control the gate of the external N-channel synchronous-rectification MOSFET.
The device quiescent current in low consumption mode is only 160μA.
Available in a 2.9mm x 2.8mm 6-pin SOT23-6L package

Note: More technical information can be found in the datasheet linked at the bottom of this page and in the SRK1000A and SRK10000B product pages.