TNY274-280
OUTPUT POWER TABLE
230 VAC ±15%
85-265 VAC
PRODUCT
ILIMIT-1
ILIMIT
ILIMIT+1
ILIMIT-1
ILIMIT
ILIMIT+1
TNY274 P or G
TNY275 P or G
TNY276 P or G
TNY277 P or G
TNY278 P or G
TNY279 P or G
TNY280 P or G
9
10.9
12
9.1
15.1
19.4
23.7
28
7.1
8.4
8.5
9.3
7.1
10.8
11.8
15.1
19.4
23.7
28
11.8
15.1
18.5
21.8
25.2
28.5
15.3
19.6
24
9.2
11.9
15.3
18.6
22
11.8
15.1
18.5
21.8
28.4
32.7
32.2
36.6
25.4
Table 2. Minimum Practical Power at Three Selectable Current Limit Levels.
For best performance of the OVP function, it is recommended
thatarelativelyhighbiaswindingvoltageisused,intherangeof
15V-30V. Thisminimizestheerrorvoltageonthebiaswinding
due to leakage inductance and also ensures adequate voltage
during no-load operation from which to supply the BP/M pin
for reduced no-load consumption.
practically eliminates audible noise. Vacuum impregnation
of the transformer should not be used due to the high primary
capacitanceandincreasedlossesthatresult.Higherfluxdensities
are possible, however careful evaluation of the audible noise
performance should be made using production transformer
samples before approving the design.
Selecting the Zener diode voltage to be approximately 6 V
above the bias winding voltage (28 V for 22 V bias winding)
gives good OVP performance for most designs, but can be
adjusted to compensate for variations in leakage inductance.
Adding additional filtering can be achieved by inserting a low
value (10 Ω to 47 Ω) resistor in series with the bias winding
diode and/or the OVP Zener as shown by R7 and R3 in
Figure 14. The resistor in series with the OVPZener also limits
the maximum current into the BP/M pin.
Ceramic capacitors that use dielectrics such as Z5U, when used
in clamp circuits, may also generate audio noise. If this is the
case, try replacing them with a capacitor having a different
dielectric or construction, for example a film type.
TinySwitch-lll Layout Considerations
Layout
See Figure 15 for a recommended circuit board layout for
TinySwitch-III.
Reducing No-load Consumption
AsTinySwitch-IIIisself-poweredfromtheBP/Mpincapacitor,
there is no need for an auxillary or bias winding to be provided
onthetransformerforthispurpose. Typicalno-loadconsumption
whenself-poweredis<150mWat265VACinput. Theaddition
ofabiaswindingcanreducethisdownto<50mWbysupplying
theTinySwitch-IIIfromthelowerbiasvoltageandinhibitingthe
internal high voltage current source. To achieve this, select the
value of the resistor (R8 in Figure 14) to provide the data sheet
DRAIN supply current. In practice, due to the reduction of the
bias voltage at low load, start with a value equal to 40% greater
thanthedatasheetmaximumcurrent,andthenincreasethevalue
of the resistor to give the lowest no-load consumption.
Single Point Grounding
Useasinglepointgroundconnectionfromtheinputfiltercapacitor
to the area of copper connected to the SOURCE pins.
Bypass Capacitor (CBP)
The BP/M pin capacitor should be located as near as possible
to the BP/M and SOURCE pins.
Primary Loop Area
The area of the primary loop that connects the input filter
capacitor, transformer primary and TinySwitch-III together
should be kept as small as possible.
Audible Noise
Primary Clamp Circuit
The cycle skipping mode of operation used in TinySwitch-III
can generate audio frequency components in the transformer.
To limit this audible noise generation the transformer should
be designed such that the peak core flux density is below
3000 Gauss (300 mT). Following this guideline and using the
standard transformer production technique of dip varnishing
Aclamp is used to limit peak voltage on the DRAIN pin at turn
off. This can be achieved by using an RCD clamp or a Zener
(~200 V) and diode clamp across the primary winding. In all
cases, to minimize EMI, care should be taken to minimize the
circuit path from the clamp components to the transformer and
TinySwitch-III.
E
2/06
10
POWERINT [ Power Integrations ]
