參數(shù)資料
型號(hào): L6566BTR
廠商: 意法半導(dǎo)體
英文描述: Multi-mode controller for SMPS
中文描述: 多模式開關(guān)電源控制器
文件頁(yè)數(shù): 26/51頁(yè)
文件大?。?/td> 401K
代理商: L6566BTR
Application information
L6566B
26/51
5.5
PWM control block
The device is specific for secondary feedback. Typically, there is a TL431 on the secondary
side and an optocoupler that transfers output voltage information to the PWM control on the
primary side, crossing the isolation barrier. The PWM control input (pin 9, COMP) is driven
directly by the phototransistor’s collector (the emitter is grounded to GND) to modulate the
duty cycle (
Figure 14
, left-hand side circuit).
In applications where a tight output regulation is not required, it is possible to use a primary-
sensing feedback technique. In this approach the voltage generated by the self-supply
winding is sensed and regulated. This solution, shown in
Figure 14
, right-hand side circuit,
is cheaper because no optocoupler or secondary reference is needed, but output voltage
regulation, especially as a result of load changes, is quite poor.
Figure 14. Possible feedback configurations that can be used with the L6566B
Ideally, the voltage generated by the self-supply winding and the output voltage should be
related by the Naux/Ns turn ratio only. Actually, numerous non-idealities, mainly
transformer's parasitics, cause the actual ratio to deviate from the ideal one. Line regulation
is quite good, in the range of ± 2%, whereas load regulation is about ±5% and output
voltage tolerance is in the range of ±10%.
The dynamics of the pin is in the 2.5 to 5V range. The voltage at the pin is clamped
downwards at about 2 V. If the clamp is externally overridden and the voltage on the pin is
pulled below 1.4V the L6566B will shut down. This condition is latched as long as the device
is supplied. While the device is disabled, however, no energy is coming from the self-supply
circuit, thus the voltage on the Vcc capacitor will decay and cross the UVLO threshold after
some time, which clears the latch and lets the HV generator restart. This function is
intended for an externally controlled burst-mode operation at light load with a reduced
output voltage, a technique typically used in multi-output SMPS, such as those for TVs or
monitors (see the timing diagram
Figure 15 on page 27
).
Vout
TL431
L6566B
9
COMP
L6566B
5 Vcc
N
aux
9
COMP
Cs
Secondary feedback
Primary feedback
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