STR-A6000MZ datasheet(17/26 Pages) SANKEN

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STR-A6000MZ/HZ Series

STR-A6000MZ/HZ - DS Rev.1.2

SANKEN ELECTRIC CO.,LTD.

Mar.13, 2015

VOCP' becomes a constant value VOCP(H) = 0.888 V

ONTime

DPC

)

(

OCP







)

AVG

(

OSC

)

(

OCP

ONDuty

DPC







(6)

where,

VOCP(L): OCP Threshold Voltage at Zero ON Duty (V)

DPC: OCP Compensation Coefficient (mV/μs)

ONTime: On-time of a power MOSFET (μs)

ONDuty: On duty of a power MOSFET (%)

fOSC(AVG): Average PWM Switching Frequency (kHz)

9.11 Overload Protection (OLP)

Figure 9-17 shows the FB/OLP pin peripheral circuit,

and Figure 9-18 shows each waveform for Overload

Protection (OLP) operation.

When the peak drain current of ID is limited by

Overcurrent Protection operation, the output voltage,

VOUT, decreases and the feedback current from the

secondary photo-coupler

becomes

zero.

Thus,

the

feedback current, IFB, charges C3 connected to the

FB/OLP pin and FB/OLP pin voltage increases. When

the FB/OLP pin voltage increases to VFB(OLP) = 7.3 V or

more for the OLP delay time, tOLP = 75 ms or more, the

OLP is activated, the IC stops switching operation.

During OLP operation, the Bias Assist Function is

disabled. Thus, VCC pin voltage decreases to VCC(OFF),

the control circuit stops operation. After that, the IC

reverts to the initial state by UVLO circuit, and the IC

starts operation when the VCC pin voltage increases to

VCC(ON) by startup current. Thus, the intermittent

operation by UVLO is repeated in OLP state.

This intermittent operation reduces the stress of parts

such as a power MOSFET and a secondary side rectifier

diode.

addition,

this

operation

reduces

power

consumption because the switching period in this

intermittent operation is short compared with oscillation

stop period. When the abnormal condition is removed,

the IC returns to normal operation automatically.

PC1

FB/OLP

VCC

GND

IFB

Figure 9-17 FB/OLP pin peripheral circuit

VCC pin voltage

FB/OLP pin voltage

Drain current,

VCC(OFF)

VFB(OLP)

tOLP

VCC(ON)

Non-switching interval

tOLP

Figure 9-18 OLP operational waveforms

9.12 Overvoltage Protection (OVP)

When the voltage between the VCC pin and the GND

pin increases to VCC(OVP) = 29.1 V or more, Overvoltage

Protection (OVP) is activated and the IC stops switching

operation.

During OVP operation, the Bias Assist Function is

disabled, the intermittent operation by UVLO is repeated

(refer to Section 9.11). When the fault condition is

removed,

the

returns

normal

operation

automatically (refer to Figure 9-19). When VCC pin

voltage is provided by using auxiliary winding of

transformer, the overvoltage conditions such as output

voltage detection circuit open can be detected because

the VCC pin voltage is proportional to output voltage.

The approximate value of output voltage VOUT(OVP) in

OVP condition is calculated by using Equation (7).





)

NORMAL

(

)

NORMAL

(

OUT

OUT(OVP)

29.1(V)

(7)

where,

VOUT(NORMAL): Output voltage in normal operation

VCC(NORMAL): VCC pin voltage in normal operation

VCC pin voltage

Drain current,

VCC(OFF)

VCC(ON)

VCC(OVP)

Figure 9-19 OVP operational waveforms

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