A switched mode converter is disclosed that includes both voltage mode and
current mode control. The switched mode converter also includes mode
logic for switching between a voltage mode and a current mode. The
converter includes current sensing circuitry for sensing the switcher
current on the primary side of the transformer and the load current on
the secondary side as well as voltage sensing circuitry for sensing the
converter output voltage. When the load current is less than a
predetermined value, the converter operates in a voltage mode. During the
voltage mode, the output voltage of the voltage mode controller is used
to control the duty cycle of a pulse width modulation (PWM) controller.
When the load current is greater than a predetermined value, the
converter operates in a current mode. In a current mode, the primary
switcher current is used to control the PWM controller. As such, during a
light load in which the converter is voltage controlled, there is no need
for a minimum load to stabilize the control loop. In a current-mode, the
control loop will have a relatively faster transient response and avoid
flux imbalance in push-pull topology. As such, the converter provides the
advantages of both known voltage controlled and current controlled
switched mode converters. In addition, by the careful arrangement of the
locations of a EMC filter, a primary heat sink, a secondary heat sink, a
power transformer T1 and other power devices as well as a cooling fan, a
smaller EMC filter can be used due to the primary heat sink performing a
dual function of thermal management and additionally providing EMC
shielding to prevent the noise, for example, the noise generated by the
transformer, from reaching the filter. In addition, the primary heat sink
is configured to face the air flow while the secondary heat sink is
placed close to the fan with its fin direction the same as the direction
of the air flow. As such, both the primary and the secondary heat sink
get maximum air flow, allowing smaller heat sinks to be used in order to
provide a reliable and cost-effective switched mode converter.