DN05108/D

Design Note – DN05108/D

High Efficiency DC-DC Converter Module
DeviceApplication

Input Voltage

Output PowerNCP12700Module

9 to 36 Vdc

Up to 15 W

CCM/DCM
Flyback

I/O Isolation
Isolated

Output Specification

Output Voltage
Nominal Current
Full Load Efficiency
Startup Time
Over Power Protection
Over Voltage Protection

12 Vdc nominal
1.25 A> 87%< 30 ms
120 % - 150 %16 VdcCircuit Description
The NCP12700 is fixed frequency, peak current mode
PWM controller for single-ended switch mode power
supplies (SMPS). Among its many features are a bestin-class startup linear regulator; programmability ofswitching frequency, soft start, and over-powerprotection; fully integrated slope compensation, andmultiple protection functions necessary for designingefficient industrial, telecom, and transportation DC-DC
power supplies with a minimum number of external
components.
This design note describes a 12 V, 15 W flyback SMPS
developed with the NCP12700BDNR2G controller. TheSMPS operates from an input voltage range of 9 – 36 V
while achieving greater than 87% full load efficiency.
The SMPS was designed to operate in both continuousand discontinuous conduction mode depending on load
current and input voltage.
A full circuit schematic, bill of materials, transformer
design details, and PCB artwork are provided. The
design note also contains multiple operational
waveforms and performance data highlighting thefeatures and capabilities of the NCP12700.

January 2018, Rev. 0Topology

Key Features
 Wide Input Range (9 – 120/200 V;
MSOP10/WQFN10) Startup Regulator
 Startup Regulator Circuit capable of sourcing aminimum of 15 mA
 Programmable Over-Power Protection
 Integrated Slope Compensation
 Fault Input for Over Temperature and Output
Over Voltage Fault Conditions, NTC Compatible 1 A / 2.8 A Source / Sink Gate Driver Programmable Soft Start Overload Protection with 30 ms Timer and 1 s
Auto-recovery

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DN05108/D

Circuit SchematicJanuary 2018, Rev. 0

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DN05108/D

Magnetics Design – Flyback Transformer

January 2018, Rev. 0

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DN05108/D

Full Load Efficiency

Vin (V)Pin (W)

Po (W)

Efficiency (%)

917.21

15.18

88.18

1216.85

15.18

90.09

18

16.67

15.18

91.05

24

16.68

15.1791.00

36

16.69

15.18

90.93

Vin (V)Pin (W)

Po (W)

Efficiency (%)

9

17.08

15.04

88.07

913.53

12.05

89.09

910.06

9.02

89.71

96.78

6.08

89.64

93.41

3.00

87.76

18

16.56

15.04

90.85

18

13.28

12.05

90.72

18

9.92

9.02

90.92

18

6.75

6.08

90.03

18

3.43

3.00

87.32

Full Load Efficiency > 88%
Figure 1: Full Load Efficiency vs. Input Voltage

Average Efficiency

January 2018, Rev. 0

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DN05108/D
36

16.62

15.06

90.58

36

13.46

12.06

89.61

36

10.10

9.02

89.32

366.90

6.08

87.99

36

3.64

3.01

82.75

Figure 2: Average Efficiency vs Output PowerJanuary 2018, Rev. 0

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DN05108/D

Description of Key Features

1. High Voltage Startup Regulator
9 VIN

36 VIN

Figures 3: Startup Regulator Operation

Startup Regulator Operation
Ch. 1 (Yellow): VIN
Ch. 2 (Blue): VCC
Ch. 3 (Purple): VOUT
Ch. 4 (Green): DRV

The NCP12700 features a high voltage startup regulator capable of operating from input voltages ranging
from 9 – 200 V. The regulator is capable of sourcing > 15 mA with as little as 2 V of overhead. A capacitor inthe range 1 – 10 µF at the VCC pin is recommended to ensure stability of the regulator. The input operating
range, source current capability, and stability requirements of the regulator were designed for best-in-classperformance providing the user with fast startup capability and requiring no additional components for ease ofdesign. The regulator’s drive capability ensures that the device can continue to self-bias for the duration of thestartup period easing the design of the auxiliary winding. Once the application is in regulation it isrecommended that an auxiliary winding from the power transformer be utilized for biasing of the supply toreduce the thermal stress on the controller.
The startup waveforms for the DC-DC Module at 9 and 36 V are shown in Figure 3. The VCC voltage isquickly charged to 8 V, enabling switching of the application within 2.5 ms of the input power being applied.
The application module reaches regulation in less than 25 ms and no voltage drop is observed on VCC
demonstrating the source capability of the regulator.

January 2018, Rev. 0

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6DN05108/D

2. Input Over-Power Compensation

In wide input range power supplies the power delivery capability tends to increase at higher line voltages
presenting thermal challenges for the supply designer. The NCP12700 features an integrated input over-powerprotection feature for limiting the output power capability of the application at higher line voltages. Shown inthe Figure 4, the controller tracks an image of the input line voltage through the UVLO pin and sources current
out of the current sense pin as the UVLO pin voltage increases. A series resistor between the CS pin at thecontroller and the current sensing element creates an offset voltage reducing the available peak current in thepower supply and thereby reducing the power delivery capability. The current out of the CS pin has been limited
to 200 µA allowing the designer to utilize the series resistor commonly included for high frequency filtering ofthe CS signal.

Figure 4: Over Power Protection Circuit

Figure 5: Over Power Protection Waveform

Ch. 1 (Yellow): COMPVCC
Ch. 2 (Blue): CS @ Pin
Ch. 3 (Purple): CS @ RSNS
Ch. 4 (Green): DRV

The waveform in Figure 5 demonstrates the offset voltage and reduced peak current capability in thedemonstration board. The waveform in blue shows how the current sense voltage at the controller is increased
relative to the voltage across the current sensing element.

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DN05108/D
The plot in Figure 6 shows the power supply overload current as a function of input voltage. The available
overload current is practically constant across the input voltage showing the benefit of the over-power protection
feature.

Figure 6: Overload Current vs Input Voltage3. Slope Compensation
Peak current mode controlled power supplies are susceptible to subharmonic oscillations when operatingin continuous conduction mode at higher duty cycles. The NCP12700 features fully integrated slope
compensation effective for damping out the oscillations and ensuring a stable operating power supply. Figure 7
illustrates the basic principle of the integrated slope compensation in the NCP12700. A voltage ramp is
subtracted from the drive terminating signal of a comparator in the PWM reset path. The ramp begins
subtracting from the signal at a 40% duty cycle and ends at the 80% maximum duty cycle limit with a peak
subtraction of 100 mV. The slope compensation is applied to both the PWM and Current Limit comparator
ensuring stable operation regardless of the drive terminating comparator. The waveform in Figure 8 illustrates
the compensating slope while showing the CS and COMP pin waveforms. The power supply operating in CCM
at 60% duty cycle is in stable operation with no indication of subharmonic oscillation.

Figure 7: Slope Compensation Operation

January 2018, Rev. 0

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DN05108/D

Figure 8: Slope Compensation Waveforms

Ch. 2 (Blue): CS
Ch. 3 (Purple): COMP
Ch. 4 (Green): DRV

January 2018, Rev. 0

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9DN05108/D

Bill of Materials

REF DESC1 - C4, C35, C36
C5C6, C7, C13
C8C9C10
C11C12
C14 - 16
C17C24
C25, C26, C27, C28
C30
C33
CT1CY1
D1, D4, D5, D9
D3D6D8D10D11D13J1, J2
L1
M1
P1 - P5
Q1
R1
R2
R3
R4
R5, R11, R15
R6
R7, R13, R14, R17,R25, R30
R8, R8A
R9R10
R12
R16
R18, R18A
R19
R20R21, R23, R24, R27,R28, R29
R22, R26
R31
RT1
TP1 - 5, 9 - 11

QTY6131111131141111411111121151111
13
1

Description
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, C0G
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
Capacitor, Ceramic, X7R
DNP
Capacitor, Ceramic, X7T
Capacitor, Ceramic, X7R
Current Sense Transformer
Capacitor, Ceramic, X7R
Diode, Switching
Diode, Fast recovery
Diode, Zener
Diode, Zener
DNP
Diode, Switching
Diode, Schottky
Terminal Block, 2 pos, in-line
Power Inductor, Shielded
Transistor, MOSFET, Power
Printed Circuit Pin
Transistor, NPN, General Purpose
Resistor, 1/4 W
Resistor, 1/10 W
Resistor, 1/8 W
Resistor, 1/10 W
Resistor, 1/10 W
Resistor, 1/10 W

Value
2.2 uF, 100 V
2.2 uF, 50 V
10 nF, 50 V
22 nF, 50 V
1 nF, 50 V
100 pF, 50 V
4.7 uF, 50 V
6800 pF, 630 V
22 uF, 25 V
47 uF, 16 V
470 pF, 100 V
DNP
0.1 uF, 250 V
2.2 uF, 50 V
1:100; 2 mH
1 nF, 250 Vac
200 V, 0.2 A
600 V, 1 A
10 V, 300 mW
15 V, 300 mW
DNP
250 V, 0.2 A, Dual
100 V, 10 A
300 V, 10 A
4.7 uH, 4.5 A
100 V, 50 A
8A
40 V, 0.6 A
64.9 kΩ
7.5 kΩ
4.99 Ω
49.9 kΩ10 Ω
2.2 Ω

Tolerance
20%
10%
10%10%
10%
5%10%10%10%10%10%Footprint
SMD, 1210
SMD, 1206
SMD, 0603
SMD, 0603
SMD, 0603SMD, 0603
SMD, 1206
SMD, 0805
SMD, 1210
SMD, 2917
SMD, 0603

Manufacturer
Kemet
Samsung
Yageo
Yageo
Yageo
Yageo
MurataKemet
MurataPanasonic
MurataManufacturer PN
C1210C225M1RACTU
CL31B225KBHNNNE
CC0603KRX7R9BB103
CC0603KRX7R9BB223
CC0603KRX7R9BB102
CC0603JRNPO9BN101
GRM31CR71H475KA12L
C0805C682KBRACTU
GRM32ER71E226KE15L
EEF-CX1C470R
GRM188R72A471KA01D

10%10%

SMD, 0805
SMD, 0603
SMD, 5300_CST_8P
SMD, 1808
SMD, SOD-323
SMD, SMA
SMD, SOD-323
SMD, SOD-323

TDK
MurataMurata
Johanson Dielectric
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor

C2012X7T2E104K125AA
GRM188R61H225KE11D
53100C
502R29W102KV3E-X1Y2-SC
BAS20HT1G
MURA160T3G
MM3Z10VT1G
MM3Z15VT1G

1%
1%
1%1%1%1%

SMD, SC-88A
SMD, SOIC8_FL5
TH, 2POS, LS3.5MM
IHLP_2020
SMD, SOIC8_FL5
TH, 1POS, D1.02mm
SOT-23
SMD, 1206
SMD, 0603
SMD, 0805
SMD, 0603
SMD, 0603
SMD, 0603

ON Semiconductor
ON Semiconductor
Phoenix Contact
VishayON Semiconductor
Mill-MaxON Semiconductor
StackpoleStackpole
Stackpole
Stackpole
Stackpole
Stackpole

BAS21DW5T1G
NTS10100MFST1G
1984617
IHLP2020CZER4R7M11
NTMFS6B14NT1G
1179-0-00-15-00-00-33-0
MMBT2222ALT1G
RMCF1206FT64K9
RMCF0603FT7K50
RMCF0805FT4R99
RMCF0603FT49K9
RMCF0603FT10R0
RMCF0603FT2R20

Substitution
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
Yes
Yes
No
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes

6Resistor 1/10 W

10 kΩ

1%

SMD, 0603

Stackpole

RMCF0603FT10K0Yes2111121
1

DNP - JUMPER TO GND
Resistor, 1/10 W
Resistor, 1/8 W
Resistor, 1/10 W
Resistor, 1/10 W
Resistor, 1/4 W
Resistor, 1/10 W
Resistor, 1/10 W

750
20 kΩ
38.3 kΩ2 kΩ
100 Ω
4.99 kΩ9.31 Ω

1%1%1%1%1%1%1%

SMD, 0603
SMD, 1206
SMD, 0603
SMD, 0603
SMD, 1206
SMD, 0603
SMD, 0603

Stackpole
Stackpole
Stackpole
Stackpole
Stackpole
Stackpole
Stackpole

RMCF0603FT750R
RMCF1206FT20K0
RMCF0603FT38K3
RMCF0603FT2K00
RMCF1206FT100RRMCF0603FT4K99
RMCF0603FT9R31Yes
Yes
Yes
Yes
Yes
Yes
Yes

6DNP

DNP

2118Resistor, 1/10 W
Resistor, 1/4 W
NTC Thermistor
Testpoint, Red, 40 mil0Ω0Ω
100 kΩ

1%
1%
1%

SMD, 0603
SMD, 1206
SMD, 0805
TH, 1POS, D1.02mm

Stackpole
Stackpole
VishayKeystone Electronics

RMCF0603ZT0R00
RMCF1206ZT0R00
NCTS0805E3104JMT
5000

Yes
Yes
Yes
Yes

TX1

1

Flyback Transformer

U1U2
U3111

PWM Controller
Optocoupler
Shunt Regulator

January 2018, Rev. 012 uH, 6.25 A, Np:Ns =1:1
50 mA, 80-160%
36 V, 100 mA

10%20%

No

SMD, RM6, Custom

Wurth Electronics

750316765 REV01

No

SMD, Micro-10, 3x3 mm
SMD, SSOP-4
SOT-23

ON Semiconductor
Fairchild
ON Semiconductor

NCP12700BDNR2GHMHA2801A
NCP431AVSNT1G

No
No
No

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DN05108/D

Demo Board

References
NCP12700 Datasheet
NCP431 Datasheet

January 2018, Rev. 0

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