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參數資料
| 型號： | 935269485115 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 穩壓器 |
| 英文描述： | SWITCHING CONTROLLER, 115 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | 1.50 MM, PLASTIC, MO-178, SOT-25, SOT-23, SOP-5 |
| 文件頁數： | 5/21頁 |
| 文件大小： | 298K |
| 代理商： | 935269485115 |
Philips Semiconductors
Product data
SA57251-XX
CMOS switching regulator (PWM controlled)
2001 Aug 01
13
Designing a passive snubber
If the switching power supply is generating too much radio
frequency interference (RFI) a passive snubber can be added.
A passive snubber is a series resistor and capacitor placed across
any component that exhibits a resonant “ringing”. This series R-L-C
loop creates a lossy or damped tank circuit that dissipates the
ringing energy. The design is critical, because it introduces another
loss within the converter.
Designing a snubber is an empirical process, mainly because it
involves undefined parasitic capacitances and inductances
contributed by the PCB layout, leakage inductance, and device
capacitances. The snubber should be placed across the major
source of the spike or ringing which is the output rectifier for a boost
converter (see Figure 20) and the primary windings of the
transformer in a flyback transformer (see Figure 25).
The usual design process is:
1. Measure the period of the undesired ringing (T0).
2. Place a very small ceramic capacitor (about 10 pF) across the
output rectifier or primary winding.
3. Re-measure the period of the undesired ringing. The new period
should be about 3 times that of T0. If it is less than this, place a
slightly larger value of capacitor across the output rectifier or
primary winding.
4. Once the desired increase in the ringing period is achieved with
a capacitance (C0), place a resistor in series with the capacitor
whose value is approximately:
R
snubber ^
T
0
2
pC
0
Eqn. (10)
This should produce a snubber that does not load the circuit and
introduces a very small loss.
SL01499
SA57251-XX
VIN
CIN
ON/OFF
GND
FB
COUT
VOUT
DRIVE
PASSIVE SNUBBER
Figure 25. Passive snubber in flyback converter.
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