ML4828 Ver la hoja de datos (PDF) - Micro Linear Corporation
Número de pieza
componentes Descripción
Fabricante
ML4828 Datasheet PDF : 11 Pages
| |||
FUNCTIONAL DESCRIPTION
PHASE MODULATOR
The ML4828 controls the power of a full bridge power
section by modulating the phases of the switches of the A
and B sides (Figure 1). The power cycle starts with A2 and
B1 high, as shown in the timing diagram (Figure 2).
1. With A2 and B1 high, Q1 and Q2 are ON. Current
flows through the primary of the transformer, and
power is delivered to the output through the secondary
winding (not shown).
2. After either the ΦMOD or ILIM comparator trips, B1
goes low, turning off Q2. Energy in the primary winding
charges the parasitic capacitances of Q2 and Q3 to
+VIN during tDB.
3. B2 goes high after time tDB, which is set by the resistor
connected from RB (pin 2) to GND. tDB should be set
large enough such that the source of Q3 has been
ML4828
charged to +VIN. At this time, Q3 turns on at zero
voltage. The transformer is now effectively shorted
through Q1 and Q3, with the primary magnetizing
current circulating in the loop formed by the
transformer primary, Q1, and Q3.
4. CLOCK then goes high and A2 goes low, while A1
remains low for time tDA, which is set by the resistor
connected from RA (pin 1) to GND. During this time,
both Q1 and Q4 are OFF. The primary magnetizing
current discharges the parasitic capacitances of Q1 and
Q4 to GND.
5. A1 goes high after time tDA. At this point, the drain of
Q4 is discharged to GND, and Q4 turns on at zero
voltage. With both Q3 and Q4 ON, a new power cycle
starts, and power is delivered to the output.
The above sequence is then repeated with the roles of
side A and B interchanged.
The ML4828 can also be used in current mode by sensing
the load current on the RAMP input (pin 11).
A2
B2
TB
+VIN
Q3
Q1
TA
B1
ML4828
A1
ILIM
B
TB
LLEAKAGE
TRANSFORMER
Q2
Q4
RSENSE
A
TA
Figure 1. Simplified diagram of Phase Modulated power Outputs.
CT
CLOCK
A2
tDA
A1
tDA
B1
tDA
tPD1
B2
tDB
tPD1
tDB
tPD1
tDB
B
A
Figure 2. Phase Modulation control waveforms (Shaded areas indicate a power cycle).
5
Share Link: 