ONSEMI AND8019

AND8019/D
Offline Converter Provides
5.0 Volt, 1.0 Amp Output for
Small Electronic Equipment
Prepared by: Alan Ball
ON Semiconductor
http://onsemi.com
APPLICATION NOTE
General Description
ON Semiconductor’s NCP1000 series of offline
converters offers a low cost, high efficiency power source
for low power, electronic equipment. It serves the same
function as small, line frequency transformers, but with the
added benefits of line and load regulation, transient
suppression, reduction in weight, and operation across the
universal input voltage range.
This kit provides a 5.0 volt, 1.0 amp output, which is
derived from an input source of 85 to 265 VAC, and 50 Hz
to 60 Hz. This range of input voltages will allow this circuit
to function virtually anywhere in the world without
modification. The output is regulated and current limited.
Both common mode and differential mode EMI filtering are
incorporated on the ac line.
Features
•
•
•
•
•
•
•
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Output Well Regulated Over Changes in Line and Load
Minimal Parts Count
Universal Input Voltage Range
100 kHz Switching Frequency
Power Switch and Current Sense Built into Chip
No External Startup Circuit Required
Thermal Shutdown Circuitry Included
Board Designed for EMI and UL Approvals
Parts List
Cap, ceramic, 1.0 F, 10 V, 0603
TDK
C1608X5R1A105K
C6
Cap, ceramic, .01 F, 50 V, 0603
TDK
C1608X7R1A103K
C7, C11
Cap, Alum elect, 10 F, 25 V
Panasonic
ECA–1EM100
C8
Cap, Alum elect, 1500 F, 6.3 V
Panasonic
EEU–FCOJ152
C9, C10
Cap, class X1, 1.0 nF, 440 Vac
Vishay/Roederstein
WYO102MCMBFOK
C12
Diode, Rectifier, 600 V, 1.0 A
ON Semiconductor
1N4005
D1–D4
Rectifier, Schottky, 40 V, 3.0 A
ON Semiconductor
MBRS340T3
D5
Diode, Switching, 70 V, 200 mA
ON Semiconductor
MMBD6050LT1
D6
Diode, Ultra–Fast 600 V, 1.0 A,
ON Semiconductor
MUR160
D7
Fuse, 160 mA, 250 Vac
Cooper Bussman
BK/ETF–160MA
F1
Inductor, 33 H
Cooper Coiltronics
UP0.4C–330
L1
Connector
Beau
830502
P1, P2
Resistor, 470 , 5%
Vishay/Dale
CRCW1206–471–5%
R1
Resistor, 4.7 k, .25 W, 5%
–
R2
Resistor, 270 , 5%
Vishay/Dale
CRCW1206–271–5%
R3
Resistor, 2.0 k, 5%
Vishay/Dale
CRCW1206–2k1%
R4, R5
Resistor, 6.8 , .25 W, 5%
–
R6, R7
Reference
Resistor, 10 , .25 W, 5%
–
R8, R9
ECQ–U2A823MV
C1
Transformer, flyback
Cooper Coiltronics
CTX13–14602
T1
Cap, Alum elect, 10 F, 450 V
Panasonic
EEU–EB2W100
C2, C3
IC, Switching Regulator
ON Semiconductor
NCP1000P
U1
Cap, ceramic, 2.2 pF, 1000 Vac
Panasonic
ECK–D3A222KBP
C4
Optocoupler
Lumex
67–1560–5
U2
Cap, Alum elect, 3.3 F, 25 V
Panasonic
ECE–A1EKK3R3
C5
IC, Voltage Regulator
ON Semiconductor
TL431AID
U3
Description / Manufacturer
Part Number
Cap, x–series, .082 F, 250 Vac
Panasonic
 Semiconductor Components Industries, LLC, 2002
June, 2002 – Rev. 4
1
Publication Order Number:
AND8019/D
AND8019/D
Manufacturers Contact Data
Mfr.
Board Evaluation
Phone
Web
ON Semiconductor
800 282–9855 www.onsemi.com
Cooper Electronics
561 752–5000 www.cooperet.com
TDK
847 803–6100
Mallory
317 273–0090 www.nacc–doesit.com
Vishay/...
818 781–1642 www.vishay.com/index.html
Lumex
847 359–2790 www.lumex.com
Beau Interconnect
603 524–5101 www.beauint.com
Panasonic
–
The following Power Supply Test Setup diagram and
description is designed to allow the board to be tested for all
parameters listed in the Converter Test Data table. This may
be used to confirm proper operation of the board, as well as
operating parameters of modified boards.
www.component.tdk.com
www.panasonic.com
1A
Scope
500 mA
90 mA
85 vac–265 vac
50 Hz–60 Hz
V
55 Volt
or
Watt
Meter
UUT
12 10 Load Fixture
Figure 1. Power Supply Test Setup
Test Setup
Measurement Techniques
The input power source needs to be variable over the range
of voltages and frequencies that you choose to test. This can
be either a variac or an electronic power source.
Connect it to a voltmeter or wattmeter. A wattmeter will be
required to measure efficiency. If none is available, use a
voltmeter. The output of the meter will be fed into the input
connector on the board. The polarity is not important as this
converter has an isolated output. Please keep in mind that the
input side of this circuit is hot – including the ground.
The output connector should be connected to an ammeter
in the high line, and then to a set of load resistors. The 12 and 10 resistors should be rated at 10 watts, and the 55 at 2.0 watts.
Any lab scope with at least a 20 MHz bandwidth will be
adequate to observe ripple and switching waveforms.
The unit will not be damaged by input voltages below
85 volts, but may not operate properly. Do not exceed the
265 volt rating as this could damage the NCP1000 as well as
other components.
To accurately measure the output voltage and ripple, the
voltmeter and oscilloscope probes should be connected as
close as possible to the output terminals of the board.
Measuring the output voltage at the load resistors will result
in errors due to the impedance of the ammeter and of the lead
wires.
Ripple measurements often contain large amounts of
common mode noise. Before taking measurements, connect
the scope probe to the ground lead at the negative output
terminal. Any spikes that are on the screen of the scope are
common mode noise that is being picked up by the scope
leads, and are not part of the output ripple. This phenomenon
may be reduced by using two scope probes in a differential
measurement mode.
Connect both ground leads to the negative output
terminal. Connect one scope probe to the negative terminal
also, and the other to the positive terminal. Set the scope up
to subtract the ground signal from the ripple signal, and the
resulting waveform will be a more accurate representation
of the ripple.
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AND8019/D
Regulation
Converter Test Data
To measure line regulation, hold the load constant and
vary the input over the desired range taking measurements
at convenient intervals. The change in output voltage for a
fixed load, across the range of input voltages is the line
regulation.
Load regulation is measured in a similar manner. The line
is held constant and the output voltage is measured as the
load is varied from minimum to maximum.
Ripple
The scope should be connected as described in the
Measurement Techniques section, and should be ac coupled.
Peak–to–peak ripple is the measurement from the lowest
point to the highest point on the trace. If a peak–to–mean
measurement is desired, set the scope input to ground, move
the trace on top of the center graticule line of the scope, and
then set the scope coupling back to ac. The voltage from the
lowest point on the trace and the highest point on the trace,
to the center graticule line are the peak–to–mean
measurements.
Parameter
Conditions
Line Regulation
85 V ≤ Vin ≤ 265 V
Vo = 6.0 mV
Data
Load Regulation
0 A ≤ Io ≤ 1.0 A
Vo = 8.0 mV
Combined Line/
Load Regulation
85 V ≤ Vin ≤ 265 V
0 A ≤ Io ≤ 1.0 A
Vo = 10 mV
Output Ripple
Io = 1.0 A
100 mVpp
Input Power
Vin = 115 V, Io = 1.0 A
Vin = 220 V, Io = 1.0 A
7.75 watts
7.88 watts
Power Factor
Vin = 115 V, Io = 1.0 A
Vin = 220 V, Io = 1.0 A
–0.57
–0.49
Efficiency
Vin = 115 V, Io = 1.0 A
Vin = 220 V, Io = 1.0 A
= 66%
= 64%
Troubleshooting
Symptom
Solution
Unit does not
turn on, does not
draw current
1. Assure that ac source and meter are
properly connected by measuring the
voltage at the input connector.
2. Measure the voltage across C2. If it is
not approximately equal to the peak input
voltage, check for wrong or defective
components (R6, R7, D1–D4).
3. Observe voltage at pin 1 of U1. This
voltage needs to exceed 8.5 volts for
unit to start, and remain greater than
7.5 volts for unit to operate. If not in this
range check for shorts, and assure that
pin 5 is greater than 50 volts, otherwise
replace chip.
4. Measure the voltage at pin 2 of U1.
It should measure less than 4.5 volts for
PWM to be active. If it is, and the output
is not switching, the NCP1000 may be
defective.
Unit does not
turn on, draws
excessive current
1. Check for obvious shorts on the board
and remove if found.
2. Disconnect all leads and measure
resistance across C2. If no short is found,
check test setup. If a short is found,
isolate it by removing components and
testing (D1–D4, C2, U1).
• Unit does
1. Assure that the input voltage and output
current are in the specified ranges.
2. Measure voltage across C8. It should be
at least twice the output voltage. If not,
check D6, L2 and C8.
3. Check the voltage at pin 2. If it is greater
than 4.5 volts the opto may be shorted,
if 0 the opto may open or C4 may be
shorted.
4. Measure voltage at pin 8 of U3 and
measure voltage drop across R3. If:
Efficiency
Efficiency is defined as:
= Pout/Pin = (Vo Io) / Pin
The output power is the output voltage multiplied by the
output current. The input power must be read from a quality
wattmeter with a wide bandwidth due to the harmonic
content of the input current waveform. There is no accurate
method of measuring the input power by the use of DVM’s
or oscilloscopes.
Most wattmeters will also measure power factor, line
voltage and line current.
Transient Loads
Rapid changes in the load of a power converter cause the
output voltage to increase or decrease for a short period of
time. If the circuit that will be attached to this converter is
sensitive to small excursions in voltage, it is highly
recommended to test the unit under similar transients. The
following exercise will test the unit for a transient from
250 mA to 1.0 A and from 1.0 A to 250 mA. If the actual load
transient is different, the loads should be modified to reflect
those conditions.
Response to load transients can be observed by causing a
step load change and synching the oscilloscope to this event.
The best way to do this is to replace the switch on the 500 mA
load (10 resistor) with a FET. An ON Semiconductor
MTD3302 transistor, driven by a pulse generator with a
0 volt to 10 volt pulse will make a simple electronic switch.
Figures 8 and 9 show the transient response to an output load
change of 10% to 100% load.
Observing the output voltage on an oscilloscope during
this event will allow measurement of the level of
perturbation as well as the duration.
not regulate
•
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•
•
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V8 < 2.5 volts & VR3 = 0 then replace U2.
V8 < 2.5 volts & VR3 > 0 then replace U3.
V8 > 2.5 volts & VR3 = 0 then replace U3.
V8 > 2.5 volts & VR3 > 0 then replace U2.
AND8019/D
Theory of Operation
As the output approaches a short circuit condition, the
auxiliary winding voltage will reduce along with the output
voltage. When the auxiliary winding is reduced below the
UVLO shutdown level, the unit will shutdown, and time out
for eight Vcc charging cycles, to reduce power dissipation,
before restarting. Due to leakage inductance spikes, the
auxiliary voltage may not track the output voltage
proportionally. If short circuit protection is required, it is
recommended that a secondary side current limit circuit be
used to assure unit will be completely protected under short
circuit conditions.
Input
The ac source is connected to the input terminals of this
unit. Fuse F1 is a safety device for fire protection and not
intended to protect the circuit from overcurrent conditions.
C1, R6 and R7 comprise the input EMI filter. Diodes D1–D4
rectify the ac line which is then filtered by capacitor, C2.
Primary Power Circuit
The NCP1000 power switching regulator chip contains
the control circuit, startup circuit and power switch circuit.
The startup circuit allows a small amount of current from
pin 5 to charge C8 and C5. When this voltage reaches
approximately 8.5 volts, the unit will commence operation
as can be observed at pin 5. Once the unit begins switching,
it’s power is derived from the auxiliary winding of the
transformer through D6 and C8. Power from C8 is delivered
to pin 1.
C5 provides energy storage at pin 1. R1, which is placed
in series between the aux winding supply (C8) and pin 1,
limits the current into the VCC pin. The VCC voltage is
supplied by the aux winding and limited by an internal
8.6 volt shunt regulator.
Modification of Output Voltage or Current
This circuit has been designed to provide a regulated
5.0 volt output at a maximum current of 1.0 amp. Changes
will require redesign in several areas of the circuit.
The output voltage is determined by comparing the output
of the voltage divider of R4 and R5 to the 2.5 volt internal
reference in the TL431. This resistive divider must be
modified to change the output voltage. To do this, first
choose the bias current that you want in the divider –1.0 mA
is a good rule of thumb. The voltage across R5 will always
be 2.5 volts, so the equation for R5 is:
R5 (k) = 2.5 volts / Ibias (mA)
Primary Regulation Circuit
and
The NCP1000 receives the error signal via an
opto–coupler at pin 2, the Feedback input. This input has an
internal 2.7 k resistor to ground. As current from the
opto–coupler flows into pin 2, it develops a voltage across
the internal resistor. This voltage is used as the error signal
into the PWM comparator to determine the duty cycle. As
the voltage on pin 2 increases, the duty cycle will decrease,
and therefore, the output power will decrease.
R4 = R5 (Vo – 2.5 volts) / 2.5 V
Since it is necessary to maintain a voltage of at least
9.5 volts on C8 at all times, the auxiliary winding of the
transformer will be affected by any change in output voltage.
Consult the transformer manufacturer for modifications to
this component.
Capacitors C6 and C7, and diode D5 are all affected by the
output voltage and may need to be changed depending on the
direction and magnitude of the voltage change.
Any increase in power can have effects on a number of
components. The NCP1000 can process power of at least 10
watts for a universal input, however the transformer, output
rectifier (D5) and filter caps will need to be analyzed for
their suitability.
Secondary Regulation
Regulation is accomplished by comparing the output
voltage (voltage divider R4 and R5) to a fixed reference
within the TL431 regulator. The TL431 also has an internal
amplifier which is used as the error amplifier for this circuit.
The output of the TL431 conducts a current that biases the
photodiode of U2. This in turn causes the phototransistor of
U2 to conduct and provides a voltage to the NCP1000 chip
that has the error information required for regulation. C10 is
used to compensate the internal error amplifier in the TL431
for frequency stability.
Component Substitutions
Similar components may be substituted for those on the
parts list, however, there are certain parameters for some
switching power supply components that need to be
considered when doing so.
Rectifiers require the same voltage and current ratings as
those specified. In addition, verify that their speed is equal
to, or better than that of the specified device.
Capacitors in this type of power converter are subjected to
very high rms switching currents. Any substitutions need to
be checked to assure that the ripple current rating is better
than, or equal to that of the specified device.
Current Limit Protection
The NCP1000 includes an internal current limit circuit.
The nominal threshold is 0.50 amps peak of switch current.
If the current tries to exceed this level, the current limit
comparator will terminate the pulse at 0.50 amps. Under
current limit conditions, the output voltage will reduce as
necessary to maintain a this maximum switch current. Due
to the characteristics of a flyback converter, the unit will go
into a constant power mode in current limit. This means that
as the output voltage is reduced, the output current will
increase.
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AND8019/D
R6
6.8
F1
V in
D1 – D4
+
C2
10 F
C1
R7
6.8
+
C3
10 F
R2
4.7 k
C6
1.0 F
C9
1500 F
C10
1500 F
p/o U2
D7
1
C8
10 F
R5
2k
C7
.01 F
R8
10
R9
10
Figure 2. Schematic Diagram
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5
C11
.01 F
U3
TL431
D6
L1
33 H
NCP
1000
C5
3.3 F
C4
2.2 nF
5 V, 1 A
R3 R4
270 2 k
R1
470
p/o U2
D5
T1
C12
1 nF
RETURN
AND8019/D
Printed Circuit Board
Figure 3. Artwork – Viewed from Copper Side
Actual size is 2.50″ x 1.70″
Figure 4. Layout – Viewed from
Component Side
Figure 5. Drill Drawing
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AND8019/D
Circuit Waveforms
Vin = 115 Vrms
1 Amp Load
50 mV/div, 5 s/div
Figure 6. Ripple
Vin = 220 Vrms
1 Amp Load
50 mV/div, 5 s/div
Figure 7. Ripple
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AND8019/D
Circuit Waveforms
Vin = 115 Vac
Top Trace:
Output Voltage
100 mV/div, 1 ms/div
Bottom Trace:
0.1 Amps to 1 Amp
Figure 8. Transient Response
Vin = 220 Vac
Top Trace:
Output Voltage
100 mV/div, 1 ms/div
Bottom Trace:
0.1 Amps to 1 Amp
Figure 9. Transient Response
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AND8019/D
Pin 5 Switching Waveforms
Vin = 115 Vac
Iout = 1.0 ADC
Figure 10. Switching Waveform
(Pin 5 to Ground)
Vin = 220 Vac
Iout = 1.0 ADC
Figure 11. Switching Waveform
(Pin 5 to Ground)
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AND8019/D
Notes
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AND8019/D
Notes
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AND8019/D
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make
changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any
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AND8019/D