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MB39C602 Datasheet(Fiches technique) 11 Page - Cypress Semiconductor
Numéro de pièce
CYPRESS [Cypress Semiconductor]
MB39C602 Datasheet(HTML) 11 Page - Cypress Semiconductor
/ 40 page
Document Number: 002-08397 Rev. *A
Page 11 of 40
8. Function Explanation
1. LED Current Control Function
MB39C602 is a flyback type switching regulator controller. The LED current is regulated by controlling the switching on-time
depending on the LED load.The LED current is converted into detecting voltage (Vs) by sense resistor (Rs) connected in series
with LED. Vs is compared by an external error amplifier (Err AMP).When Vs falls below a reference voltage, Err AMP output
rises and the current that flows into the Opto-Coupler is decreased.
The OTC pin current is controlled via the Opto-Coupler in the on-time control block. In on-time control, it controls on-time at
OTC pin current. So, on-time increases when the current of the OTC pin decreases. And the average current supplied to LED is
regulated, because on-time is regulated at the constant switching frequency.
2. Cascode Switching
The switch in Primary Winding is a cascode connection.The gate of external MOSFET is connected with the VCG pin, and the
source is connected with the drain of internal Driver MOSFET. When the swich is on-state, internal Driver MOSFET is turned on,
HS Driver MOSFET is turned off, and the source voltage of external MOSFET goes down to GND. For this period the DC bias is
supplied to the gate of external MOSFET from the VCG pin. Therefore external MOSFET is turned on.
When the switch is off-state, internal Driver MOSFET is turned off, HS Driver MOSFET is turned on, and the source voltage of
external MOSFET goes up to VCG voltage. For this period the DC bias is supplied to the gate of external MOSFET from the
VCG pin. Therefore external MOSFET is turned off. Moreover, the current flowing into internal Driver MOSFET is equal to the
current of Primary Winding. Therefore, the peak current into Primary Winding can be detected without the sense resistor.
3. Natural PFC (Power Factor Correction) Function
In the AC voltage input, when the input current waveform is brought close to the sine-wave, and the phase difference is brought
close to Zero, Power Factor is improved. In the flyback method operating in discontinuous conduction mode, when the input
capacitance is set small, the input current almost becomes equal with peak current (I
) of Primary Winding.
: Supply voltage of Primary Winding
: Inductance of Primary Winding
In on-time control, if loop response of Error Amp. is set to lower than the AC frequency (below 1/10 of the AC frequency),
on-time can be constant. Therefore, input current is proportional to input voltage, so Power Factor is regulated.
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