TL494_15 Datasheet, PDF (15/33 Pages) Unisonic Technologies – VOLTAGE MODE PWM CONTROL CIRCUIT

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Typical Application (continued)
14
13
V_REF
R3
5.1 kW
TL494
R4
5.1 kW
R5
510 W
TL494
SLVS074G – JANUARY 1983 – REVISED JANUARY 2015
V_O
1
2
3
R7
51 kW
Error
+ ^Amplifier
−
R8
5.1 kW
R9
5.1 kW
TL494
Figure 11. Error-Amplifier Section
The TL494 internal 5-V reference is divided to 2.5 V by R3 and R4. The output-voltage error signal also is
divided to 2.5 V by R8 and R9. If the output must be regulated to exactly 5.0 V, a 10-kΩ potentiometer can be
used in place of R8 to provide an adjustment.
To increase the stability of the error-amplifier circuit, the output of the error amplifier is fed back to the inverting
input through R_T, reducing the gain to 101.
10.2.2.2.3 Current-Limiting Amplifier
The power supply was designed for a 10-A load current and an I_L swing of 1.5 A, therefore, the short-circuit
current should be:
I_SC
= I_O
I_L
+
2
= 10.75 A
(10)
The current-limiting circuit is shown in Figure 12.
V_O
LOAD
R11
0.1 kW
16
+ ¹⁵
TL494
14
R2
3 kW
R1
1 kW
V_REF
TL494
Figure 12. Current-Limiting Circuit
Resistors R1 and R2 set the reference of about 1 V on the inverting input of the current-limiting amplifier.
Resistor R13, in series with the load, applies 1 V to the noninverting terminal of the current-limiting amplifier
when the load current reaches 10 A. The output-pulse width is reduced accordingly. The value of R13 is:
1V
R13 =
= 0.1W
10 A
(11)
10.2.2.2.4 Soft Start and Dead Time
To reduce stress on the switching transistors at start-up, the start-up surge that occurs as the output filter
capacitor charges must be reduced. The availability of the dead-time control makes implementation of a soft-start
circuit relatively simple (see Figure 13).
Copyright © 1983–2015, Texas Instruments Incorporated
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