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TEA1623PH Datasheet(PDF) 6 Page - NXP Semiconductors |
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TEA1623PH Datasheet(HTML) 6 Page - NXP Semiconductors |
6 / 20 page TEA1623P_TEA1623PH All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved. Product data sheet Rev. 3 — 30 August 2010 6 of 20 NXP Semiconductors TEA1623P; TEA1623PH STARplug switched mode power supply controller IC relative sensitivity of the duty factor to the regulation voltage at low duty factor is almost equal to the sensitivity at high duty factors. This results in a more constant gain over the duty factor range compared to PWM systems with a linear sawtooth oscillator. Stable operation at low duty factors is easily realized. For high efficiency, the frequency is reduced as soon as the duty factor drops below a certain value. This is accomplished by increasing the oscillator charge time. To ensure that the capacitor can be charged within the charge time, the value of the oscillator capacitor should be limited to approximately 1 nF. 8.3 Duty factor control The duty factor is controlled by the internal regulation voltage and the oscillator signal on pin RC. The internal regulation voltage is equal to the external regulation voltage ( −2.5 V) multiplied by the gain of the error amplifier (typical 20 dB or 10 ×). The minimum duty factor of the switched mode power supply is 0 %. The maximum duty factor is set to 75 % (typical value at 100 kHz oscillation frequency). 8.4 Valley switching A new cycle is started at the primary stroke when the switch is switched on (see Figure 5). After a certain time (determined by the RC oscillator voltage and the internal regulation level), the switch is turned off and the secondary stroke starts. The internal regulation level is determined by the voltage on pin REG. After the secondary stroke, the drain voltage shows an oscillation with a frequency of approximately , where: Lp is the primary self inductance on the drain node. Cp is the parasitic capacitance on the drain node. As soon as the oscillator voltage is high again and the secondary stroke has ended, the circuit waits for a low drain voltage before starting a new primary stroke. The primary stroke starts some time before the actual valley at low ringing frequencies, and some time after the actual valley at high ringing frequencies. Figure 6 shows a typical curve for a reflected voltage N × V o of 80 V. This voltage is the output voltage Vo (see Figure 7) transferred to the primary side of the transformer with the factor N (determined by the turns ratio of the transformer). Figure 6 shows that the system switches exactly at minimum drain voltage for ringing frequencies of 480 kHz, thus reducing the switch-on losses to a minimum. At 200 kHz, the next primary stroke is started at 33 ° before the valley. The switch-on losses are still reduced significantly. 1 2 π L pCp × ----------------------------- |
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