onsemi Secondary Side Regulated Isolated Flyback Converter Instruction Manual
- June 12, 2024
- onsemi
Table of Contents
onsemi Secondary Side Regulated Isolated Flyback Converter
SPECIFICATION
Devices
| Applications| Input Voltage| Output Power| Topology| Board Size
---|---|---|---|---|---
NCV12711| Automotive| 4 − 45 V dc| 12 W| Current−Mode Flyback|
100 x 47 x 15 mm
Output Spec|
Turn on Time
| Efficiency| Operating Temperature| Cooling| Standby Power
12 V/1 A| < 100 ms| Peaks to 89 % @ full load| 0 – 50°C| Open Frame in Still
Air|
See the tables on page 8
DESCRIPTION
This evaluation board user’s manual provides elementary information about a
secondary side regulated flyback converter NCV12711SSRGEVB built with the
NCV12711 operated in current−mode control at 100 kHz. This control circuit
offers many features to build an energy−efficient converter with all the
needed protections like cycle−by−cycle current limit with a 250−mV sense
voltage, over−current protection (OCP) and over−voltage protection (OVP) on
the VCC pin. The controller drives an N−channel MOSFET as with any classical
flyback converter at a user−adjustable switching frequency. The secondary side
hosts a low−Vf diode for efficient rectification in continuous conduction mode
(CCM).
The primary−side section drives a transformer whose primary inductance is 8 H.
The current is sensed via two paralleled 40−m resistors which limit the
maximum output current to a safe value in fault condition. The board is rated
to 12 W of continuous output power in free air at the lowest input voltage.
This level is delivered down to a 4.5−V input. The converter is able to
deliver output power up to 4−V input, which is the turn−off level adjusted by
an UVLO resistor divider. At higher input voltages, the board may deliver more
power but thermal runaway may happen and the board temperature must be
monitored.
The regulation is ensured directly on secondary side requiring the use of an
optocoupler. The advantage of this solution is better output voltage
regulation in comparison with Primary−Side−Regulated converter.
The switch SW1 let you select different configurations to test the circuit:
- a is closed, b open: in this mode, the VCC and VIN pin are connected together while the auxiliary winding is not used. The maximum input voltage is 25 V; going beyond this value will trip the OVP on VCC pin.
- b is closed, a open: in this mode, the controller is supplied by the VIN pin only during start−up sequence and VCC is biased by the rectified auxiliary supply. The input voltage can go up to 45 V.
- a and b are open: the controller is self−supplied via internal LDO and the auxiliary winding is not used. The input voltage can go up to 45 V.
Due to secondary side regulation, the switch SW1 affects only the efficiency
of the system. For more details, see the Efficiency and Standby data in TEST
DATA section. The internal operational amplifier coupled to external
components ensures the realization of a type 2 compensator. Using the
simulation model or a bench measurement, components values were adjusted to
crossover above 1 kHz.
The maximum crossover is limited by the right−half−plane−zero (RHPZ) which
degrades the phase response at the lowest input voltage and the largest
output current. The board is equipped with two connectors letting you easily
connect the network analyzers probes for a convenient measurement. The
collected graphs show a comfortable phase margin at crossover.
A simple front−end filter limits the amount of parasitic noise going back to
the source and it must be properly damped to avoid interaction with the
downstream converter. C9 is providing that function with its equivalent
series\ resistance (ESR).
KEY FEATURES OF NCV12711
- Internal 20−mA current source for lossless start−up sequence and self−supply operation
- Smooth start−up sequence with frequency sweep
- Internal operational amplifier with precise 2.5−V reference voltage
- Current−mode control operation
- Short circuit protection
- Over voltage protection
- Input Voltage UVLO with Hysteresis
- Shutdown threshold for external disable
- 0% duty ratio mode for low standby power
- Single Resistor Programmable Oscillator
- User−Adjustable Soft−Start Ramp
EVALUATION BOARD SCHEMATIC DIAGRAM
Figure 2. Schematic of the NCV12711SSRGEVB Evaluation Board
MAGNETICS DATA
ZA9654−AE from Coilcraft:
Figure 3. Mechanical Specifications
Figure 4. Electrical Specifications
TEST DATA
Startup Time
Steady−state Operation
Load Transient Response
Output Voltage Ripple
Drain−Source Voltage
Standby Data
Table 1. NO−LOAD INPUT POWER WHEN THE IC IS SELF−SUPLIED VIA LDO
VIN (V)
| IIN (mA)| PIN (mW)|
VOUT (V)
---|---|---|---
4.5
| 10.9| 49.0| 12.1
15| 6.0| 89.5|
12.1
25
| 4.2| 106.0| 12.1
45| 3.6| 164.3|
12.1
Table 2. NO−LOAD INPUT POWER WHEN THE VCC PIN IS CONNECTED TO VIN PIN
| VIN (V) | IIN (mA) | PIN (mW) | VOUT (V) |
|---|
4.5
| 11.2| 50.6| 12.1
15| 6.0| 90.0|
12.1
25
| 4.3| 106.5|
12.1
Table 3. NO−LOAD INPUT POWER WHEN THE VCC PIN IS CONNECTED TO AUX WINDING
VIN (V)
| IIN (mA)| PIN (mW)|
VOUT (V)
---|---|---|---
4.5
| 24.7| 111.3| 12.1
15| 10.5| 156.5|
12.1
25
| 5.0| 125.5| 12.1
45| 2.8| 125.1|
12.1
Efficiency Data
Table 4. BILL OF MATERIALS
Designator
| Qty| Description| Value| Tolerance| Footprint| Manufacturer|
Manufacturer Part Number
---|---|---|---|---|---|---|---
C1
| 1| Ceramic capacitor| 10 nF/100 V| 20%| 0805| Generic|
C2| 1| Ceramic capacitor| 22 pF/10 V| 20%| 0805| Generic|
C3
| 1| Ceramic capacitor| 4.7 µF/50 V| 10%| 1206| TDK| CGA5L3X7R1H475K160AB
C4| 1| Ceramic capacitor| 10 nF/10 V| 10%| 0805| Generic|
C5, C13, C14
| 3| Electrolytic capacitor| 330 µF/16 V| 20%| TH| Rubycon| 16ZLG330MEFC8X11.5
C6| 1| Ceramic capacitor| 22 nF/10 V| 10%| 0805| Generic|
C7, C8, C18
| 3| Ceramic capacitor| 0.1 µF/50 V| 10%| 0805| Generic|
C9| 1| Electrolytic capacitor| 100 µF/50 V| 20%| TH| Rubycon|
50ZL100MEFC8X11.5
C10, C11
| 2| Ceramic capacitor| 2.2 µF/100 V| 10%| 1210| Kemet| C1210C225M1RACTU
C12| 1| Electrolytic capacitor| 4.7 µF/25 V| 20%| TH| Generic|
C15
| 0| Ceramic capacitor| NU| −| 0805| Generic|
C16| 1| Ceramic capacitor| 1 nF/16 V| 10%| 0805| Generic|
C17
| 1| Ceramic capacitor| 470 pF/100 V| 10%| 0805| Generic|
C19| 1| Ceramic capacitor| 3.3 nF/630 V| 10%| 1206| Kemet|
C1206C332KBRACTU
D1
| 1| HV diode| 1N4937| −| DO−41| onsemi| 1N4937G
D2| 1| Power diode| FSV10120V| −| TO−277| onsemi|
FSV10120V
D3
| 1| Signal diode| MMSD914| −| SOD−123| onsemi|
D4| 1| Signal diode| BAV21| −| SOD−123| onsemi|
D5
| 0| Zener diode 12 V| NU| −| SOD−123| onsemi| MMSZ4699T1G
J1a, J2a| 2| Banana plug| −| −| | multicomp|
24.243.1
J1b, J2b
| 2| Banana plug| −| −| | multicomp| 24.243.2
L3| 1| Inductor| 1.5 µH| 30%| | Coilcraft|
MSS1038−152NL
R1
| 1| Resistor| 18 kQ| 1%| 2512| Generic|
R2, R13| 2| Resistor| 40 mQ| 1%| 2512| Vishay|
WSL2512R0400FEA
R3
| 1| Resistor| 845 Q| 1%| 0805| Generic|
R4| 1| Resistor| 1.5 kQ| 1%| 0805| Generic|
R5
| 1| Resistor| 68 kQ| 1%| 0805| Generic|
R6, R11, R17| 3| Resistor| 10 kQ| 1%| 0805| Generic|
R7
| 1| Resistor| 133 kQ| 1%| 0805| Generic|
R8, R18, R19| 0| Resistor| NU| 1%| 0805| Generic|
R9
| 1| Resistor| 560 Q| 1%| 0805| Generic|
R10, R16| 2| Resistor| 10 Q| 1%| 0805|
Generic
|
R12, R14
| 2| Resistor| 100 Q/0.5 W| 1%| 0805| Generic|
R15| 1| Resistor| 38 Q| 1%| 0805| Generic|
R20
| 1| Resistor| 2.2 Q| 1%| 0805| Generic|
R21, R100| 2| Resistor| 0 Q| 1%| 0805| Generic|
R22
| 1| Resistor| 1 Q| 1%| 0805| Generic|
R23| 1| Resistor| 33 Q| 1%| 0805|
Generic
|
SW1
| 1| PCB Switch| | −| | multicomp| MCNDS−02V
T1| 1| Transformer| ZA9654−AE| −| | Coilcraft|
ZA9654−AE
Q1
| 1| N−Channel MOSFET| FDMS86103L| −| PQFN−8| onsemi|
FDMS86103L
U1
| 1| PWM controller| NCV12711| −| MSOP−10| onsemi| NCV12711A
U2| 0| Optocoupler| NU| −| SSOP−4| Renesas|
U3
| 1| Optocoupler| PS2801C−1| −| SSOP−4| Renesas|
U4
| 1| Shunt Regulator| NCP431| −| SOT−23| onsemi|
NCP431
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