MC44603P ON Semiconductor, MC44603P Datasheet - Page 17
Manufacturer Part Number
Other Power Management Voltage/Current PWM
PWM Mode Controllerr
Specifications of MC44603P
Input Voltage Range
Package / Case
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
arrangement is not activated, the operating frequency can be
obtained from the graph in Figure 2.
NOTE: The output is disabled by the signal V
Synchronization and Demagnetization Blocks
output must be low. Reset is activated by the L
during the discharge phase. To restart, the L
(refer to Figure 35). To perform this, the demagnetization
signal and the synchronization must be low.
that compare the synchronization signal (external) to 0.7 and
3.7 V (typical values). The comparators’ outputs are
connected to the input of an AND gate so that the final output
of the block should be:
synchronized low level pulses have to be generated on the
output of the synchronization block. If synchronization is
not required, the Pin 9 must be connected to the ground.
saturation of the transformer core, or demagnetization,
consists in using the auxiliary winding voltage. This voltage
DV is the oscillator peak−to−peak value
So, as f
To enable the output, the L
The synchronization block consists of two comparators
− high when 0.7 < SYNC < 3.7 V
− low in the other cases.
As a low level is necessary to enable the output,
In flyback applications, a good means to detect magnetic
− negative during the on−time,
− positive during the off−time,
− equal to zero for the dead−time with generally some
ringing (refer to Figure 38).
is lower than 1.0 V (refer to Figure 31).
is the oscillator charge current
is the oscillator charge time
is the oscillator discharge current
is the oscillator discharge time
= 1 /(T
Figure 37. Synchronization
) when the Regul
has to be set
consists of a comparator that can compare the auxiliary
winding voltage to a reference that is typically equal to
applied voltages while an active clamping system limits the
negative voltages to typically −0.33 V. This negative clamp
level is sufficient to avoid the substrate diode switching on.
incorporated in order to keep the demagnetization block
output level low as soon as a voltage lower than 65 mV is
detected and as long as a new restart is produced (high level
on the output) (refer to Figure 39). This process prevents
ringing on the signal at Pin 8 from disrupting the
demagnetization detection. This results in a very accurate
connected to the output, disabling it during the
demagnetization phase (refer to Figure 34).
NOTE: The demagnetization detection can be inhibited by
connecting Pin 8 to the ground.
That is why, the MC44603A demagnetization detection
A diode D has been incorporated to clamp the positive
In addition to the comparator, a latch system has been
The demagnetization block output is also directly
Power Losses in a Classical Flyback Structure
Figure 38. Demagnetization Detection
Figure 39. Demagnetization Block