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MB39C605PNF-G-JNEFE1 数据表(PDF) 13 Page - Cypress Semiconductor |
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MB39C605PNF-G-JNEFE1 数据表(HTML) 13 Page - Cypress Semiconductor |
13 / 26 page Document Number: 002-08444 Rev. *B Page 13 of 26 MB39C605 8.4 Power-Off Sequence After the AC line voltage is removed, VBULK is discharged by switching operation. Since any Secondary Winding current does not flow, ILED is supplied only from output capacitors and decreases gradually. VVDD also decreases because there is no current supply from both Auxiliary Winding and VBULK. When VVDD falls below the UVLO threshold voltage, MB39C605 shuts down. Figure 8-5. Power-Off Waveform DRV VDD VLED UVLO Vth = 7.9V Shutdown VBULK0 AC line removed VBULK 8.5 IP_PEAK Detection Function MB39C605 detects Primary Winding peak current (IP_PEAK) of Transformer. ILED is set by connecting a sense resistance (Rcs) between CS pin and GND pin. Maximum IP_PEAK (IP_PEAKMAX) limited by Over Current Protection (OCP) can also be set with the resistance. Using the Secondary to Primary turns ratio (NP/NS) and ILED, RCS is set as the following equation (refer to 8.1) RCS= S P N N × LED I 0.14 In addition, using the OCP threshold voltage (VOCPTH) and RCS, IP_PEAKMAX is calculated with the following equation. IP_PEAKMAX = R V CS OCPTH 8.6 Zero Voltage Switching Function MB39C605 has built-in zero voltage switching function to minimize switching loss of the external switching MOSFET. This device detects a zero crossing point through a resistor divider connected from TZE pin to Auxiliary Winding. A zero energy detection circuit detects a negative crossing point of the voltage on TZE pin to Zero energy threshold voltage (VTZETL). On-timing of switching MOSFET is decided with waiting an adjustment time (tADJ) after the negative crossing occurs. tADJ is set by connecting an external resistance (RADJ) between ADJ pin and GND pin. Using Primary Winding inductance (LP) and the parasitic drain capacitor of switching MOSFET (CD), tADJ is calculated with the following equation. tADJ= 2 C × L π D P Using tADJ, RADJ is expressed by the following calculation. RADJ [kΩ] = 0.0927 × tADJ [ns] |
类似零件编号 - MB39C605PNF-G-JNEFE1 |
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类似说明 - MB39C605PNF-G-JNEFE1 |
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