參數(shù)資料
型號(hào)： TK75003
廠商： TOKO Inc.
英文描述： PWM CONTROLLER
中文描述： 脈寬調(diào)制控制器
文件頁(yè)數(shù)： 10/14頁(yè)
文件大?。?/td> 108K
代理商： TK75003
Page 10
January 1999 TOKO, Inc.
TK75003
APPLICATION INFORMATION
SELF-BIASED POWER SUPPLY WITH CONSTANT-
FREQUENCY CURRENT-MODE CONTROL
Figure 3(a) shows the TK75003 IC in the typical application:
a flyback converter with self-bias and constant-frequency
current- mode control. Figure 3(b) shows the feedback pin
voltage. In the converter, the voltage-error amplifier (a
TL431 shunt regulator IC) is located at the output side and
the error signal is transmitted to the input side through the
opto-coupler OC. Three signals are added together at the
feedback pin: 1) the feedback voltage that develops across
the resistor R
, 2) the switch current signal, and 3) the
stabilizing ramp. In each cycle, the MOSFET switch is
turned off when the sum of those three signals reaches
0.98 V.
FIGURE 3: TK75003 IN A SELF-BIASED FLYBACK
CONVERTER WITH CONSTANT-FREQUENCY
VOLTAGE-MODE CONTROL
(a) SCHEMATIC (b) VOLTAGE AT FEEDBACK PIN
POWER SUPPLY WITH CONSTANT-FREQUENCY
VOLTAGE-MODE CONTROL AND CYCLE-BY-CYCLE
CURRENT LIMIT
Voltage-mode control is free from some of the
disadvantages (e.g., subharmonic instability and noise
sensitivity) of current-mode control. It is very easy to
implement that control method with the TK75003 IC.
Figure 4(a) shows the IC in a voltage-mode-controlled
flyback converter. Figure 4(b) shows the feedback pin
voltage. The only circuit difference between current-mode
control and voltage-mode control is in the connection of
the resistor R
1
, that terminates the feedback pin. In current-
mode control, that resistor is connected to the current-
sense resistor of the converter. In voltage-mode control,
that resistor is connected to ground.
In voltage-mode control, overload protection can be realized
by adding a simple circuit to the control IC, as shown in the
figure. The PNP transistor Q
, turns on and pulls up the
feedback pin when the switch current times the resistance
of the sense R
reaches the threshold set by the resistive
divider R
2
and R
3
and the base-emitter voltage of Q
1
.
FIGURE 4: TK75003 IN A VOLTAGE-MODE-
CONTROLLED CONVERTER WITH ADDITIONAL
CYCLE-BY-CYCLE CURRENT LIMIT
(a) SCHEMATIC (b) VOLTAGE AT FEEDBACK PIN
POWER SUPPLY WITH CONSTANT OFF-TIME
CURRENT-MODE CONTROL
The advantages of constant off-time current-mode control
over constant-frequency current-mode control are: 1) there
is no need for a stabilizing ramp, 2) the converter is free
from subharmonic instability (i.e., there is no need for
slope compensation), and 3) the line voltage variation is
automatically canceled in buck-derived converters (e.g.,
the forward converter). Figure 5 shows the implementation
of that control method. As can be seen, a transistor Q
1
must be added to the controller. Figure 6 shows the timing-
pin and feedback pin voltages for the TK75003. The
transistor Q
keeps the timing pin at ground potential
during the on-time of the switch. Timing begins when the
drive output returns to low and Q
is turned off. The off-time
for typical charge and discharge currents and peak and
valley voltages is:
GND
VCC
CT
FB
DRV
CAUX
R1
VAUX
RST
VIN
n3
n2
D3
RS
OC
TL431
+
+
VOUT
D2
FEEDBACK
VOLTAGE
SWITCH
CURRENT
SIGNAL
STABILIZING
RAMP
0.98 V
0
-
CT
GND
VCC
CT
FB
DRV
VAUX
VIN
RS
TL431
+
R3
Q1
R1
R2
OC
OC
FEEDBACK
PWM
0
0.98 V
(b)
(a)
(b)
(a)
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TK75003D 制造商:TOKO 制造商全稱(chēng):TOKO, Inc 功能描述:PWM CONTROLLER
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TK75003DIMG/75003 制造商:TOKO 制造商全稱(chēng):TOKO, Inc 功能描述:PWM CONTROLLER
TK75005 制造商:TOKO 制造商全稱(chēng):TOKO, Inc 功能描述:LOW-COST FLEXIBLE PWM CONTROLLER
TK75005DCMG 制造商:TOKO 制造商全稱(chēng):TOKO, Inc 功能描述:LOW-COST FLEXIBLE PWM CONTROLLER
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