·
The current in the primary side of the transformer TR3 comes to the SMPS IC (IC3 TOP223Y). The
SMPS IC has a three-pin TO-220 case and a cooler is mounted on it. It has a built-in oscillator,
overcurrent and overvoltage protection circuitry and runs at 100kHz. It starts with the current from
the primary side of the transformer and follows the current from the feedback winding.
·
Feedback current is rectified with diode D7 and filtered with capacitor C4 and enters the
optocoupler IC2 (CQY80NG). Depending on the control current coming from the secondary side,
SMPS IC keeps the output voltage constant by controlling the duty cycle of the 100kHz signal
(PWM) at the primary side of the transformer.
·
Voltages on the secondary side are as follows: -12 Volts at D8, 5 Volts at D9, 15 Volts at D10, -
22 Volts at D13.
·
Using resistors R5, R4 and R27, 5V output is divided properly for D14 operation.
·
D14 TL431 is a constant current regulator. TL431 watches the 5 volts and supplies the required
current to IC2. There are a LED and a photo transistor in IC2. The LED inside the IC2 transmits the
value of the current from D14 to phototransistor. Depending on the current gain of the
phototransistor IC3 keeps the voltage on the 5-volt-winding constant.
·
Adjustable voltage regulator IC5 (LM317) supplies 12 Volts. 12 Volts is obtained by using resis-
tors R19, R20 and R21.
·
When the device enters stand-by mode, transistor Q2 starts to conduct and pulls the adjust pin of
IC5 to ground, where this cuts 12Volts off.
·
IC6 is also an LM317 that produces 3.3 Volts output from its 5 volts input.
·
22 Volts is used to feed the VFD (Vacuum Fluorescent Display) driver IC on the front panel.
Using diode D17 22V is decreased about 5.6V and connected to the filament winding to pro-
duce the DC offset for the filaments.
·
Transistor Q3 and zener diode D18 are used to re12 Volts. This voltage is used to feed
op-amps on the back panel.
TOP221-227
TOPS
witch -II
F
amily
T
hree
-
terminal
O
ff
-
line
PW M S
witch
Figure 1. Typical Flyback Application.
easier. The standard 8L PDIP package option reduces cost in
lower power, high efficiency applications. The internal lead
frame of this package uses six of its pins to transfer heat from
the chip directly to the board, eliminating the cost of a heat sink.
TOPSwitch incorporates all functions necessary for a switched
mode control system into a three terminal monolithic IC: power
MOSFET, PWM controller, high voltage start up circuit, loop
compensation and fault protection circuitry.
P
roduct
H
ighlights
Lowest cost, lowest component count switcher solution
Cost competitive with linears above 5W
Very low AC/DC losses Ð up to 90% efficiency
Built-in Auto-restart and Current limiting
Latching Thermal shutdown for system level protection
Implements Flyback, Forward, Boost or Buck topology
Works with primary or opto feedback
Stable in discontinuous or continuous conduction mode
Source connected tab for low EMI
Circuit simplicity and Design Tools reduce time to market
D
escription
The second generation TOPSwitch-II family is more cost
effective and provides several enhancements over the first
generation TOPSwitch family. The TOPSwitch-II family extends
the power range from 100W to 150W for 100/115/230 VAC
input and from 50W to 90W for 85-265 VAC universal input.
This brings TOPSwitch technology advantages to many new
applications, i.e. TV, Monitor, Audio amplifiers, etc. Many
significant circuit enhancements that reduce the sensitivity to
board layout and line transients now make the design even
PI-1951-091996
AC
IN
D
S
C
CONTROL
TOPS
witch
¨
