AP3965/66/71

Document number: DS36531 Rev. 3 - 2

7 of 13

www.diodes.com

November 2013

© Diodes Incorporated

AP3965/66/71

A Product Line of

Diodes Incorporated

Constant Voltage Operation

The AP3965/66/71 captures the auxiliary winding feedback voltage at FB pin and operates in constant-voltage (CV) mode to regulate the output

voltage. Assuming the secondary winding is master, the auxiliary winding is slave during the D1 on-time. The auxiliary voltage is given by:

()

d

S

AUX

AUX

V

Vo

N

N

V

+

⋅

=

…………(5)

Figure 3. Auxiliary Voltage Waveform

The voltage detection point is portion of Tons after D1 is turned on. The CV loop control function of AP3965/66/71 then generates a D1 off-time to

regulate the output voltage.

Constant Current Operation

The AP3965/66/71 is designed to work in constant current (CC) mode. Figure 4 shows the secondary current waveforms.

Figure 4. Secondary Current Waveform

In CC operation, the CC loop control function of AP3965/66/71 will keep a fixed proportion between D1 on-time Tons and D1 off-time Toffs by

discharging or charging the built-in capacitance connected. This fixed proportion is

2

4

Toffs

Tons = ………… (6)

The relation between the output constant-current and secondary peak current Ipks is given by:

Toffs

Tons

Tons

Ipks

2

1

+

⋅

⋅

=

…………(7)

At the instant of D1 turn-on, the primary current transfers to the secondary at an amplitude of:

Ipk

N

N

Ipks

S

=

…………(8)