参数资料
型号: L6566BH
厂商: STMICROELECTRONICS
元件分类: 稳压器
英文描述: SWITCHING CONTROLLER, 300 kHz SWITCHING FREQ-MAX, PDSO16
封装: ROHS COMPLIANT, SOP-16
文件页数: 17/48页
文件大小: 768K
代理商: L6566BH
Application information
L6566BH
24/48
Doc ID 16610 Rev 1
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 L6566BH
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 parasites, 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 5 V 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 1.4 V the L6566BH 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 25).
Vout
TL431
L6566BH
9
COMP
L6566BH
5
Vcc
Naux
9
COMP
Cs
Secondary feedback
Primary feedback
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