STR-A6000MZ datasheet(19/26 Pages) SANKEN

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STR-A6000MZ/HZ Series

STR-A6000MZ/HZ - DS Rev.1.2

SANKEN ELECTRIC CO.,LTD.

Mar.13, 2015

For alleviating C2 peak charging, it is effective to add

some value R2, of several tenths of ohms to several

ohms, in series with D2 (see Figure 10-1). The optimal

value of R2 should be determined using a transformer

matching what will be used in the actual application,

because the variation of the auxiliary winding voltage

is affected by the transformer structural design.

Without R2

With R2

VCC pin voltage

Output current, IOUT

Figure 10-2 Variation of VCC pin voltage and power

 Snubber Circuit

If the surge voltage of VDS is large, the circuit should

be added as follows (see Figure 10-1);

・ A clamp snubber circuit of a capacitor-resistor-

diode (CRD) combination should be added on the

primary winding P.

・ A damper snubber circuit of a capacitor (C) or a

resistor-capacitor (RC) combination should be

added between the D/ST pin and the S/GND pin.

When the damper snubber circuit is added, this

components should be connected near the D/ST pin

and the S/OCP pin.

 Phase Compensation

A typical phase compensation circuit with a secondary

shunt regulator (U51) is shown in Figure 10-3.

C52 and R53 are for phase compensation. The value of

C52 and R53 are recommended to be around 0.047μF to

0.47μF and 4.7 kΩ to 470 kΩ, respectively. They

should be selected based on actual operation in the

application.

D51

C51

R51

R52

U51

R54

R56

C52

PC1

R53

R55

L51

C53

VOUT

(-)

(+)

Figure 10-3 Peripheral circuit around secondary shunt

regulator (U51)

 Transformer

Apply proper design margin to core temperature rise

by core loss and copper loss.

Because the switching currents contain high frequency

currents, the skin effect may become a consideration.

Choose a suitable wire gauge in consideration of the

RMS current and a current density of 4 to 6 A/mm

If measures to further reduce temperature are still

necessary, the following should be considered to

increase the total surface area of the wiring:

▫ Increase the number of wires in parallel.

▫ Use litz wires.

▫ Thicken the wire gauge.

In the following cases, the surge of VCC pin voltage

becomes high.

▫ The surge voltage of primary main winding, P, is

high (low output voltage and high output current

power supply designs)

▫ The winding structure of auxiliary winding, D, is

susceptible to the noise of winding P.

When the surge voltage of winding D is high, the

VCC pin voltage increases and the Overvoltage

Protection (OVP) may be activated. In transformer

design, the following should be considered;

▫ The coupling of the winding P and the secondary

output winding S should be maximized to reduce the

leakage inductance.

▫ The coupling of the winding D and the winding S

should be maximized.

▫ The coupling of the winding D and the winding P

should be minimized.

In the case of multi-output power supply, the

coupling of the secondary-side stabilized output

winding, S1, and the others (S2, S3…) should be

maximized to improve the line-regulation of those

outputs.

Figure 10-4 shows the winding structural examples

of two outputs.

Winding structural example (a):

S1 is sandwiched between P1 and P2 to maximize

the coupling of them for surge reduction of P1

and P2.

D is placed far from P1 and P2 to minimize the

coupling to the primary for the surge reduction of

Winding structural example (b)

P1 and P2 are placed close to S1 to maximize the

coupling of S1 for surge reduction of P1 and P2.

D and S2 are sandwiched by S1 to maximize the

coupling of D and S1, and that of S1 and S2. This

structure reduces the surge of D, and improves

the line-regulation of outputs.

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