TEA19161T All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
Product data sheet Rev. 1 — 10 March 2016 21 of 46
NXP Semiconductors
TEA19161T
Digital controller for high-efficiency resonant power supply
At a positive transient (t2), a new low-power cycle is started immediately to minimize the
drop in output voltage. The measured time period, at time t2, is below the targeted burst
period. The system increases the number of burst cycles. At t3, it measures the burst
period again. In this example, the burst period is still below the targeted burst period. So,
the system increases the number of low-power cycles again and again until the measured
burst period equals the target burst period, which occurs at t4.
7.5 Optobias regulation
In a typical application, the output voltage is sensed using a TL431 and connected to the
SNSFB pin of the TEA19161T via an optocoupler (see Figure 27
). Because of the
behavior of the TL431, the current through the optocoupler is at the maximum level when
the output power is at the minimum level. It is therefore one of the most critical parameters
to achieve the required no-load input power. To achieve maximum efficiency at
low load/no-load, the TEA19161T continuously regulates the optocurrent to a low level
that is independent of the output load.
A very low optocurrent reduces the transient response of the system, because of the
parasitic capacitance at the optocoupler collector. So, the TEA19161T applies a fixed
voltage at the SNSFB pin. It measures the current through the optocoupler which defines
the required output power. Via an additional internal circuitry, which adds an offset to the
required output power, the optocurrent is continuously (slowly) regulated to the I
reg(SNSFB)
level (= 85 A). This level is independent of the output power.
At a positive load transient, the optocurrent initially decreases (see Figure 9
; I
SNSFB
). The
TEA19161T immediately increases the V
SNSCAP
which again increases the output
power.
Figure 17 shows that when the optocurrent decreases, the internal voltage across the
12 k resistor drops to below the targeted level of 1020 mV (= 85 A 12 k). The
TEA19161T then slowly increases an additional offset at the power level (P). It continues
to increase the additional offset until the optocurrent reaches the target of 85 A. At a
negative transient, the additional offset to the power level is decreased. As a result, the
output voltage increases which again increases the optocurrent. In this way, the
optocurrent is continuously regulated to the I
reg(SNSFB)
level (see Figure 9).
Fig 17. Optobias regulation
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