InnoSwitch3-CE
Applications Example
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R11
InnoSwitch3-CE
0.00ꢆ Ω
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Figure 10. 12 V, 3 A Charger/Adapter.
The circuit shown in Figure 10 is a low cost 12 V, 3 A power supply
using INN3166C. This single output design features DOE Level 6 and
EC CoC 5 compliance.
Synchronous rectification (SR) is provided by MOSFET Q1. The gate
of Q1 is turned on by secondary-side controller inside IC U1, based on
the winding voltage sensed via resistor R9 and fed into the FWD pin
of the IC.
Bridge rectifier BR1 rectifies the AC input supply. Capacitors C2 and
C3 provide filtering of the rectified AC input and together with
inductor L2 form a pi-filter to attenuate differential mode EMI.
Capacitor C4 connected at the power supply output with input
common mode choke help to reduce common mode EMI.
In continuous conduction mode of operation, the MOSFET is turned
off just prior to the secondary-side’s commanding a new switching
cycle from the primary. In discontinuous conduction mode of
operation, the power MOSFET is turned off when the voltage drop
across the MOSFET falls below a threshold of 0 V. Secondary-side
control of the primary-side power MOSFET avoids any possibility of
cross conduction of the two MOSFETs and provides extremely reliable
synchronous rectification.
Thermistor RT1 limits the inrush current when the power supply is
connected to the input AC supply.
Input fuse F1 provides protection against excess input current
resulting from catastrophic failure of any of the components in the
power supply. One end of the transformer primary is connected to
the rectified DC bus; the other is connected to the drain terminal of
the MOSFET inside the InnoSwitch3-CE IC (U1).
The secondary-side of the IC is self-powered from either the
secondary winding forward voltage or the output voltage. Capacitor
C12 connected to the BPS pin of InnoSwitch3-CE IC U1, provides
decoupling for the internal circuitry.
A low-cost RCD clamp formed by diode D1, resistors R3, R1, and
capacitor C7 limits the peak drain voltage of U1 at the instant of
turn-off of the MOSFET inside U1. The clamp helps to dissipate the
energy stored in the leakage reactance of transformer T1.
During CC operation, when the output voltage falls, the device will
directly power itself from the secondary winding. During the on-time
of the primary-side power MOSFET, the forward voltage that appears
across the secondary winding is used to charge the decoupling
capacitor C12 via resistor R9 and an internal regulator. This allows
output current regulation to be maintained down to ~3 V. Below this
level the unit enters auto-restart until the output load is reduced.
The InnoSwitch3-CE IC is self-starting, using an internal high-voltage
current source to charge the BPP pin capacitor (C13) when AC is first
applied. During normal operation the primary-side block is powered
from an auxiliary winding on the transformer T1. Output of the
auxiliary (or bias) winding is rectified using diode D2 and filtered using
capacitor C11. Resistor R10 limits the current being supplied to the
BPP pin of InnoSwitch3-CE IC (U1).
Output current is sensed between the IS and GND pins with a
threshold of approximately 35 mV to reduce losses. Once the current
sense threshold is exceeded the device adjusts the number of switch
pulses to maintain a fixed output current.
The secondary-side controller of the InnoSwitch3-CE IC provides
output voltage sensing, output current sensing and drive to a
MOSFET providing synchronous rectification. The secondary of the
transformer is rectified by SR FET Q1 and filtered by capacitors C5
and C6. High frequency ringing during switching transients that
would otherwise create radiated EMI is reduced via a snubber
(resistor R5 and capacitor C8).
The output voltage is sensed via resistor divider R4 and R8. Output
voltage is regulated so as to achieve a voltage of 1.265 V on the
FEEDBACK pin. Capacitor C9 provides noise filtering of the signal at
the FEEDBACK pin.
9
Rev. D 08/18
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