Rev. F 08/16

5

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TNY253/254/255

TNY253/254/255

Figure 6. TinySwitch Operation at Light Load.

Figure 7. TinySwitch Power-Up Timing Diagram.

Figure 8. TinySwitch Power Down Timing Diagram.

PI-2261-061198

V

DRAIN

V

EN

CLOCK

DC

DRAIN

I

MAX

BYPASS Pin Capacitor

The BYPASS pin uses a small 0.1 µF ceramic capacitor for

decoupling the internal power supply of the TinySwitch.

Application Examples

Television Standby

TinySwitch is an ideal solution for low cost, high efficiency

standby power supplies used in consumer electronic products

such as TVs. Figure 9 shows a 7.5 V, 1.3 W flyback circuit that

uses TNY253 for implementing a TV standby supply. The circuit

operates from the DC high-voltage already available from the

main power supply. This input voltage can range from 120 to

375 VDC depending on the inputAC voltage range that the TV

is rated for. Capacitor C1 filters the high-voltage DC supply,

and is necessary only if there is a long trace length from the

source of the DC supply to the inputs of the TV standby circuit.

The high-voltage DC bus is applied to the series combination

of the primary winding of T1 and the integrated high-voltage

MOSFET inside the TNY253. The low operating frequency of

the TNY253 (44 kHz), allows a low cost snubber circuit C2 and

R1 to be used in place of a primary clamp circuit. In addition

to limiting the DRAIN turn off voltage spike to a safe value,

the RC snubber also reduces radiated video noise by lowering

the dv/dt of the DRAIN waveform, which is critical for video

applications such as TV and VCR. On fixed frequency PWM

and RCC circuits, use of a snubber will result in an undesir-

able fixed AC switching loss that is independent of load. The

ON/OFF control on the TinySwitch eliminates this problem

by scaling the effective switching frequency and therefore,

switching loss linearly with load. Thus the efficiency of the

supply stays relatively constant down to a fraction of a watt of

output loading.

The secondary winding is rectified and filtered by D1 and C4 to

create the 7.5 V output. L1 and C5 provide additional filtering.

The output voltage is determined by the sum of the optocoupler

U2 LED forward drop (~ 1 V) and Zener diode VR1 voltage.

The resistor R2, maintains a bias current through the Zener to

improve its voltage tolerance.

10 W Standby

The TNY255 is ideal for standby applications that require up

to 10 W of power from 230 VAC or 100/115 VAC with doubler

circuit. The TNY255 operates at 130 kHz as opposed to 44 kHz

for TNY253/254. The higher frequency operation allows the

V

DRAIN

V

IN

0.2

Time (ms)

.4

.6

.8

1

0 V

0 V

V

DRAIN

V

IN

12 V

12 V

0

100

Time (ms)

200

300

400

500

0 V

0 V