TOP250 datasheet(22/54 Pages) POWERINT

22 / 54 page

Rev. R 10/20

TOP242-250

www.power.com

Resistor R7, C9 and C10 together with C5 and R3 provide

loop compensation.

Due to the large primary currents, all the small signal control

components are connected to a separate source node that

is Kelvin connected to the SOURCE pin of the TOPSwitch-GX.

For improved common-mode surge immunity, the bias

winding common returns directly to the DC bulk capacitor

(C1).

A High Efficiency, 250 W, 250-380 VDC Input

Power Supply

The circuit shown in Figure 43 delivers 250 W (48 V @

5.2 A) at 84% efficiency using a TOP249 from a 250 VDC

to 380 VDC input. DC input is shown, as typically at this

power level a p.f.c. boost stage would preceed this supply,

providing the DC input (C1 is included to provide local

decoupling). Flyback topology is still usable at this power

level due to the high output voltage, keeping the secondary

peak currents low enough so that the output diode and

capacitors are reasonably sized.

In this example, the TOP249 is at the upper limit of its

power capability and the current limit is set to the internal

maximum by connecting the X pin to SOURCE. However,

line sensing is implemented by connecting a 2 M

Ω resistor

from the L pin to the DC rail. If the DC input rail rises above

450 VDC, then TOPSwitch-GX will stop switching until the

voltage returns to normal, preventing device damage.

Due to the high primary current, a low leakage inductance

transformer is essential. Therefore, a sandwich winding

with a copper foil secondary was used. Even with this

technique, the leakage inductance energy is beyond the

power capability of a simple Zener clamp. Therefore, R2,

R3 and C6 are added in parallel to VR1. These have been

sized such that during normal operation, very little power

is dissipated by VR1, the leakage energy instead being

dissipated by R2 and R3. However, VR1 is essential to

limit the peak drain voltage during start-up and/or overload

conditions to below the 700 V rating of the TOPSwitch-GX

MOSFET.

The secondary is rectifed and smoothed by D2 and C9,

C10 and C11. Three capacitors are used to meet the

secondary ripple current requirement. Inductor L2 and C12

provide switching noise filtering.

A simple Zener sensing chain regulates the output voltage.

The sum of the voltage drop of VR2, VR3 and VR4 plus the

LED drop of U2 gives the desired output voltage. Resistor

R6 limits LED current and sets overall control loop DC gain.

Diode D4 and C14 provide secondary soft-finish, feeding

current into the CONTROL pin prior to output regulation

48 V@

5.2 A

+250-380

VDC

0 V

RTN

PI-2692-081204

All resistor 1/8 W 5% unless

otherwise stated.

CONTROL

TOPSwitch-GX

µF

400 V

0.1

µF

50 V

6.8

Ω

100

Ω

10 k

Ω

µF

10 V

4.7 nF

1 kV

C13

150 nF

63 V

µF

50 V

C14

µF

63 V

560

µF

63 V

C10

560

µF

63 V

C11

560

µF

63 V

C12

µF

63 V

2.2 nF Y1

µH 8A

MUR1640CT

1N4148

LTV817A

BYV26C

2 M

Ω

1/2 W

68 k

Ω

2 W

68 k

Ω

2 W

VR1

P6KE200

VR2 22 V

BZX79B22

VR3 12 V

BZX79B12

VR4 12 V

BZX79B12

CONTROL

1N4148

PERFORMANCE SUMMARY

Output Power:

250 W

Line Regulation:

± 1%

Load Regulation:

± 5%

Efficiency:

≥ 85%

Ripple:

< 100 mV pk-pk

No Load Consumption:

≤ 1.4 W (300 VDC)

TOP249Y

Figure 43. 250 W, 48 V Power Supply using TOP249.

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