AN11012_15 Datasheet, PDF (24/36 Pages) NXP Semiconductors – Using the TEA1703 to reduce standby power

NXP Semiconductors
AN11012
Using the TEA1703 to reduce standby power
8.1 General description typical application
Figure 13 and Figure 14 show a typical application of the TEA1753 low cost SMPS
controller and the TEA1703 standby controller. During standby operation, optocoupler
U2A forces VINSENSE (pin 7 of the TEA1753) low. The SMPS stops switching when the
voltage on VINSENSE drops below 0.35 V (DC).
8.2 Interfacing
To reduce standby power consumption, the TL431 reference (U4 in Figure 13 and
Figure 14) and the resistor divider R37 and R38 are switched off in standby by means of
Q7. This reduces the standby power with 5 mW to 10 mW. The values of R55, R56 and
C53 are important in relation with components R51, R52 and C51, this relationship is
explained in more detail in Section 8.7.1. Resistors R55 and R56 reduce the maximum
gate voltage and C53 creates a switch off delay.
Alternatively, R37 and R38 can be increased to reduce the standby power consumption.
This, however, reduces the accuracy of the output voltage because of the spread on the
reference input current of the TL431.
line
R1
VCC (pin 1)
R2
neutral
VINSENSE (pin 7)
R3
D1001A
R1000
R4
C20
R1001
(optional)
Q11
BC547
C21
C13
R45
D1001B
4
U2A-1
LTV-817B
3
R8
gate Q8 and Q9
D1000
019aab513
Fig 15. The proposed VSENSE circuit for minimizing the influence of the dark current
The standby information for the SMPS is obtained via optocoupler U2A. The collector of
the optocoupler is not compensated for dark current. The brownout voltage can be
influenced if there is no compensation for dark current. Figure 15 shows an alternative
circuit diagram that compensates dark currents up to 10 μA. The red colored components
in Figure 15 have to be added and components R42 and R43 can be removed in
Figure 13 and Figure 14. Diode D1001A and D1001B are available in one package.
Remark: Dark current is the current flowing through the output of the phototransistor
when it is turned off.
AN11012
Application note
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 30 March 2011
© NXP B.V. 2011. All rights reserved.
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