TOP250 datasheet(21/54 Pages) POWERINT

21 / 54 page

Rev. R 10/20

TOP242-250

www.power.com

A High Efficiency, Enclosed, 70 W, Universal

Adapter Supply

The circuit shown in Figure 42 takes advantage of several

of the TOPSwitch-GX features to reduce cost, power supply

size and increase efficiency. This design delivers 70 W at

19 V, from an 85 VAC to 265 VAC input, at an ambient of

°C, in a small sealed adapter case (4”x2.15”x1”). Full

load efficiency is 85% at 85 VAC rising to 90% at 230 VAC

input.

Due to the thermal environment of a sealed adapter, a

TOP249Y is used to minimize device dissipation. Resistors

R9 and R10 externally program the current limit level to

just above the operating peak DRAIN current at full load

and low line. This allows the use of a smaller transformer

core size without saturation during start-up or output load

transients. Resistors R9 and R10 also reduce the current

limit with increasing line voltage, limiting the maximum

overload power at high input line voltage, removing the

need for any protection circuitry on the secondary. Resistor

R11 implements an undervoltage and overvoltage sense as

well as providing line feed-forward for reduced output line

frequency ripple. With resistor R11 set at 2 M

Ω, the power

supply does not start operating until the DC rail voltage

reaches 100 VDC. On removal of the AC input, the UV

sense prevents the output glitching as C1 discharges,

turning off the TOPSwitch-GX when the output regulation is

lost or when the input voltage falls to below 40 V, whichever

occurs first. This same value of R11 sets the OV threshold

to 450 V. If exceeded, for example during a line surge,

TOPSwitch-GX stops switching for the duration of the

surge, extending the high voltage withstand to 700 V

without device damage. Capacitor C11 has been added in

parallel with VR1 to reduce Zener clamp dissipation. With

a switching frequency of 132 kHz, a PQ26/20 core can be

used to provide 70 W. To maximize efficiency, by reducing

winding losses, two output windings are used each with

their own dual 100 V Schottky rectifier (D2 and D3). The

frequency reduction feature of the TOPSwitch-GX eliminates

any dummy loading to maintain regulation at no load and

reduces the no-load consumption of the power supply to

only 520 mW at 230 VAC input. Frequency jittering provides

conducted EMI meeting the CISPR 22 (FCC B) / EN55022B

specification, using simple filter components (C7, L2, L3 and

C6), even with the output earth grounded.

To regulate the output, an optocoupler (U2) is used with a

secondary reference sensing the output voltage via a

resistor divider (U3, R4, R5, R6). Diode D4 and C15 filter

and smooth the output of the bias winding. Capacitor C15

µF) prevents the bias voltage from falling during zero to

full load transients. Resistor R8 provides filtering of leakage

inductance spikes, keeping the bias voltage constant even

at high output loads.

19 V

@ 3.6 A

TOP249Y

TL431

PC817A

RTN

820 H

0.1 F

3.15 A

BR1

RS805

8A 600 V

75 H

C13

0.33 F

400 V

C12

0.022 F

400 V

C11

0.01 F

400 V

RT1

1.7 A

PI-2691-042203

All resistors 1/8 W 5% unless otherwise stated.

CONTROL

TOPSwitch-GX

150 F

400 V

PERFORMANCE SUMMARY

Output Power:

70 W

Regulation:

Efficiency:

84%

Ripple:

120 mV pk-pk

No Load Consumption:

0.52 W @ 230 VAC

47 F

16 V

820 F

25 V

200 H

820 F

25 V

C14

0.1 F

50 V

820 F

25 V

C10

0.1 F

50 V

4.7 nF 50 V

0.1 F

50 V

VR1

P6KE-

200

MBR20100

C7 2.2 nF

Y1 Safety

MBR20100

1N4148

R11

2 M

1/2 W

13 M

4.7

270

1 k

562

31.6 k

56 k

R10

20.5 k

6.8

4.75 k

C15

1 F

50 V

UF4006

Figure 42. 70 W Power Supply using Current Limit Reduction with Line and Line Sensing for UV and OV.

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