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TEA1523P-N2112 データシート(PDF) 5 Page - NXP Semiconductors |
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TEA1523P-N2112 データシート(HTML) 5 Page - NXP Semiconductors |
5 / 20 page TEA152X All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved. Product data sheet Rev. 04 — 14 September 2010 5 of 20 NXP Semiconductors TEA152x SMPS ICs for low-power systems components RRC and CRC. This mode is called Pulse Width Modulation (PWM). Furthermore, a primary stroke is started only in a valley of the secondary ringing. This valley switching principle minimizes capacitive switch-on losses. 8.1 Start-up and Underoltage lockout Initially, the IC is self supplying from the rectified mains voltage. The IC starts switching as soon as the voltage on pin VCC passes the VCC(startup) level. The supply is taken over by the auxiliary winding of the transformer as soon as VCC is high enough and the supply from the line is stopped for high efficiency operation. When for some reason the auxiliary supply is not sufficient, the high-voltage supply also supplies the IC. As soon as the voltage on pin VCC drops below the VCC(stop) level, the IC stops switching and restarts from the rectified mains voltage. 8.2 Oscillator The frequency of the oscillator is set by the external resistor and capacitor on pin RC. The external capacitor is charged rapidly to the VRC(max) level and, starting from a new primary stroke, it discharges to the VRC(min) level. Because the discharge is exponential, the 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 (typically 20 dB which is 10 ×). 8.4 Valley switching A new cycle is started when the primary switch is switched on (see Figure 4). After a certain time (determined by the oscillator voltage RC 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: (1) where: Lp = primary self-inductance Cp = parasitic capacitance on drain node 1 2 π × L p C p × () × ---------------------------------------------- |
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同様の説明 - TEA1523P-N2112 |
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