TNY278GN Power Integrations, TNY278GN Datasheet - Page 8
Manufacturer Part Number
IC OFFLINE SWIT OVP OTP HV 8SMD
Specifications of TNY278GN
124 ~ 140kHz
Voltage - Output
-40°C ~ 150°C
Package / Case
8-SMD Gull Wing, 7 Leads
Input / Supply Voltage (max)
Input / Supply Voltage (min)
Duty Cycle (max)
Operating Temperature Range
- 40 C to + 150 C
No. Of Outputs
Voltage Regulator Case Style
No. Of Pins
For Use With
596-1194 - KIT DESIGN REF TINYSWITCH-III
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Rev. I 01/09
Figure 14. TNY278P, 12 V, 1 A Universal Input Power Supply.
The circuit shown in Figure 14 is a low cost, high efﬁ ciency,
ﬂ yback power supply designed for 12 V, 1 A output from
universal input using the TNY278.
The supply features undervoltage lockout, primary sensed
output overvoltage latching shutdown protection, high
efﬁ ciency (>80%), and very low no-load consumption (<50 mW
at 265 VAC). Output regulation is accomplished using a simple
zener reference and optocoupler feedback.
The rectiﬁ ed and ﬁ ltered input voltage is applied to the primary
winding of T1. The other side of the transformer primary is
driven by the integrated MOSFET in U1. Diode D5, C2, R1, R2,
and VR1 comprise the clamp circuit, limiting the leakage
inductance turn-off voltage spike on the DRAIN pin to a safe
value. The use of a combination a Zener clamp and parallel RC
optimizes both EMI and energy efﬁ ciency. Resistor R2 allows
the use of a slow recovery, low cost, rectiﬁ er diode by limiting
the reverse current through D5. The selection of a slow diode
also improves efﬁ ciency and conducted EMI but should be a
glass passivated type, with a speciﬁ ed recovery time of ≤2 μs.
The output voltage is regulated by the Zener diode VR3. When
the output voltage exceeds the sum of the Zener and opto-
coupler LED forward drop, current will ﬂ ow in the optocoupler
LED. This will cause the transistor of the optocoupler to sink
current.When this current exceeds the ENABLE pin threshold
current the next switching cycle is inhibited. When the output
85 - 265
*R5 and R8 are optional
C7 is used to adjust U1
current limit. See circuit
voltage falls below the feedback threshold, a conduction cycle
is allowed to occur and, by adjusting the number of enabled
cycles, output regulation is maintained. As the load reduces,
the number of enabled cycles decreases, lowering the effective
switching frequency and scaling switching losses with load.
This provides almost constant efﬁ ciency down to very light
loads, ideal for meeting energy efﬁ ciency requirements.
As the TinySwitch-III devices are completely self-powered, there
is no requirement for an auxiliary or bias winding on the
transformer. However by adding a bias winding, the output
overvoltage protection feature can be conﬁ gured, protecting the
load against open feedback loop faults.
When an overvoltage condition occurs, such that bias voltage
exceeds the sum of VR2 and the BYPASS/MULTIFUNCTION
(BP/M) pin voltage (28 V+5.85 V), current begins to ﬂ ow into the
BP/M pin. When this current exceeds I
shutdown circuit in TinySwitch-III is activated. This condition is
reset when the BP/M pin voltage drops below 2.6 V after
removal of the AC input. In the example shown, on opening the
loop, the OVP trips at an output of 17 V.
For lower no-load input power consumption, the bias winding
may also be used to supply the TinySwitch-III device. Resistor
R8 feeds current into the BP/M pin, inhibiting the internal high
voltage current source that normally maintains the BP/M pin
capacitor voltage (C7) during the internal MOSFET off time.
This reduces the no-load consumption of this design from
140 mW to 40 mW at 265 VAC.
the internal latching
3.5 × 7.6 mm
12 V, 1 A