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Performance Characteristics
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10.2 Output Ripple Waveforms
Figure 4
shows the transient response for a load of change from 5A to 25A. The upper trace shows
minimal output voltage droop and overshoot during the sudden change in output current shown by the
lower trace.
Figure 5
shows typical output ripple seen directly across the output capacitor, for an input voltage of 48V
and a load of 30A. This waveform is typical of most loads and input voltages.
Figure 6
and
Figure 7
show the drain voltage of Q1 with a 25A load.
Figure 6
represents an input voltage
of 38V and
Figure 7
represents an input voltage of 78V.
Figure 8
shows the gate voltages of the synchronous rectifiers. The drive from the main power transformer
is delayed slightly at turn-on by a resistor interacting with the gate capacitance. This provides improved
switching transitions for optimum efficiency. The difference in drive voltage is inherent in the topology and
varies with line voltage.
Conditions: Input Voltage = 48VDC Output Current = 5A to
Conditions: Input Voltage = 48VDC Output Current = 5A
25A Trace 1: Output Voltage Volts/div = 0.5V Trace 2:
Trace 1: Output Voltage Volts/div = 1V Horizontal Resolution
Output Current, Amps/div = 5A Horizontal Resolution =
= 1msec/div
1msec/div
Figure 3. Output Voltage
Figure 4. Transient Response
Conditions: Input Voltage = 48VDC Output Current = 30A
Conditions: Input Voltage = 38VDC Output Current = 25A
Bandwidth Limit = 25MHz Trace 1: Output Ripple Voltage
Trace 1: Q1 drain voltage Volts/div = 20V Horizontal
Volts/div = 50mV Horizontal Resolution = 2µs/div
Resolution = 1µs/div
Figure 5. Typical Output Ripple
Figure 6. Drain Voltage of Q1
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AN-1387 LM5026 Evaluation Board
SNVA117A – September 2005 – Revised May 2013
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