PKS603-607
V
DRAIN
PI-3943-031506
300
200
100
0
10
peak output power was required in low line conditions. On-time
extension is disabled during the startup of the power supply.
PeakSwitch
Operation
PeakSwitch devices operate in the current-limit mode. When
enabled, the oscillator turns the power MOSFET on at the
beginning of each cycle. The MOSFET is turned off when the
current ramps up to the current limit or when the DC
MAX
limit
is reached. Since the highest current limit level and frequency
V
DC-OUTPUT
5
0
V
EN
CLOCK
D
0
5
10
Time (s)
Figure 6. PeakSwitch Auto-Restart Operation.
the line under-voltage sense circuit prevents a
restart attempt until the AC input voltage is removed
(I
EN
<25 µA). Then the internal auto-restart latch is reset and
the power MOSFET switching will resume once the AC input
voltage is applied again (I
EN
>25 µA). This effectively provides
a latching shutdown function with AC reset during such a fault
condition.
When a brownout or line sag occurs, output regulation may be
lost and the EN/UV pin will receive no feedback (it is pulled
low). After 30 ms of no feedback, MOSFET switching is disabled.
Since the AC line is abnormally low (I
EN
<25 µA) MOSFET
switching remains disabled until normal line voltage is restored.
The power MOSFET switching will resume once the AC input
returns to normal (I
EN
>25 µA). This effectively disables the
latching shutdown function during such a condition.
Auto-Restart (UV resistor not present)
In the event of a fault condition such as output overload,
output short circuit or an open loop condition,
PeakSwitch
enters into auto-restart operation. An internal counter
clocked by the oscillator is reset every time the EN/UV pin
is pulled low. When the EN/UV pin receives no feedback
for 30 ms, the power MOSFET switching is disabled for
5 seconds (150 ms for the first auto-restart event). The
auto-restart alternately enables and disables the switching
of the power MOSFET until the fault condition is removed.
Figure 6 illustrates auto-restart circuit operation in the presence
of an output short circuit.
Adaptive Switching Cycle On-time Extension
Adaptive switching cycle on-time extension keeps the MOSFET
on until current limit is reached, instead of terminating after
the DC
MAX
signal goes low. This on-time extension is adaptive
because it only occurs after the ENABLE pin has been high
for approximately 750 µs, a condition that would arise if the
MAX
I DRAIN
V DRAIN
PI-2749-050301
Figure 7. PeakSwitch Operation at Near Maximum Loading.
V
EN
CLOCK
D
MAX
I DRAIN
V DRAIN
PI-2667-090700
Figure 8. PeakSwitch Operation at Moderately Heavy Loading.
5
Rev. I 10/06
POWERINT [ POWER INTEGRATIONS, INC. ]
