参数资料
型号: ISL6752/54EVAL1Z
厂商: Intersil
文件页数: 12/16页
文件大小: 0K
描述: BOARD DEMO FOR ISL6752 ISL6754
标准包装: 1
主要目的: 电源,ATX
输出及类型: 1,隔离
输出电压: 12V
电流 - 输出: 50A
输入电压: 350 ~ 450 V
稳压器拓扑结构: 全桥式
板类型: 完全填充
已供物品:
已用 IC / 零件: ISL6752,ISL6754
ISL6752
Determine the amount of voltage, V e , that must be added to
and Equation 21 becomes:
( 2D – V e + Δ V CS ) ? R6
V e – Δ V CS
the current feedback signal using Equation 13.
V e = 153mV
R9 = -------------------------------------------------------------
Ω
(EQ. 24)
Next, determine the effect of the magnetizing current from
Equation 18.
Δ V CS = 91mV
Using Equation 21, solve for the summing resistor, R9, from
CTBUF to CS.
R9 = 30.1k Ω
Determine the new value of R CS , R’ CS , using Equation 22.
R’ CS = 15.4 Ω
This discussion determines the minimum external ramp that
is required. Additional slope compensation may be
considered for design margin.
If the application requires deadtime of less than about
500ns, the CTBUF signal may not perform adequately for
slope compensation. CTBUF lags the CT sawtooth
waveform by 300ns to 400ns. This behavior results in a
non-zero value of CTBUF when the next half-cycle begins
The buffer transistor used to create the external ramp from
CT should have a sufficiently high gain (>200) so as to
minimize the required base current. Whatever base current
is required reduces the charging current into CT and will
reduce the oscillator frequency.
ZVS Full-Bridge Operation
The ISL6752 is a full-bridge zero-voltage switching (ZVS)
PWM controller that behaves much like a traditional hard
switched topology controller. Rather than drive the diagonal
bridge switches simultaneously, the upper switches (OUTUL,
OUTUR) are driven at a fixed 50% duty cycle and the lower
switches (OUTLL, OUTLR) are pulse width modulated on
the trailing edge.
CT
DEADTIME
when the deadtime is short.
Under these situations, slope compensation may be added
by externally buffering the CT signal as shown in Figure 7.
1
2 VREF
OUTLL
OUTLR
OUTUR
PWM
PWM
PWM
RESONANT
DELAY
PWM
3
ISL6752
OUTUL
RESDEL
4
5
WINDOW
FIGURE 8. BRIDGE DRIVE SIGNAL TIMING
R9
6
7 CT
To understand how the ZVS method operates, one must
R6
8 CS
include the parasitic elements of the circuit and examine a
full switching cycle.
VIN+
UL
UR
L L
D1
VOUT+
R CS
C4
CT
VIN-
LL
LR
D2
RTN
FIGURE 7. ADDING SLOPE COMPENSATION USING CT
Using CT to provide slope compensation instead of CTBUF
requires the same calculations, except that Equations 20
and 21 require modification. Equation 20 becomes:
FIGURE 9. IDEALIZED FULL-BRIDGE
In Figure 9, the power semiconductor switches have been
replaced by ideal switch elements with parallel diodes and
capacitance, the output rectifiers are ideal, and the
V e – Δ V CS = ----------------------
2D ? R6
R6 + R9
V
(EQ. 23)
transformer leakage inductance has been included as a
discrete element. The parasitic capacitance has been
lumped together as switch capacitance, but represents all
parasitic capacitance in the circuit including winding
12
FN9181.3
October 31, 2008
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