A 12-V/1-A Secondary Side Regulated Isolated Flyback Converter for Automotive Applications
NCV12711SSRGEVB
Specifications
| 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 μH. The current is sensed via two paralleled 40-mΩ 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:
Switch SW1 Configurations
- a is closed, b open: In this mode, the VCC and VIN pins 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
Board Pictures
Figure 1 shows the top and bottom views of the NCV12711SSRGEVB evaluation board, highlighting its compact dimensions (10 cm x 4.7 cm) and key input/output connections. The DC input range is 4.5-45 V, and the output is 12 V/1 A.
Evaluation Board Schematic Diagram
Figure 2 presents the evaluation board's schematic diagram, illustrating the NCV12711 PWM controller (U1), associated passive components, N-Channel MOSFET (Q1), transformer (T1), and output rectification circuitry, including diodes (D1-D4) and optocouplers (U3).
Magnetics Data
Figure 3 details the mechanical specifications of the transformer (ZA9654-AE from Coilcraft), including dimensions (A: Width, B: Length, C: Height, D: Coplanarity, E: Core Misalignment) and a recommended land pattern. Figure 4 presents electrical specifications for the transformer, covering inductance, DC resistance, Hi-Pot voltage, and leakage inductance.
Test Data
Startup Time
Figures 5 through 10 display oscilloscope traces illustrating the startup time for various configurations and load conditions. They show waveforms for VDRV(t), VCOMP(t), VIN(t), and VOUT(t), with startup times typically around 16 ms.
Steady-state Operation
Figures 11 through 16 present steady-state operation waveforms, including VCS(t) and VDRV(t), for different input voltages (5.5 V, 25 V, 45 V) and load currents (0 A, 1 A). These figures detail parameters such as switching frequency (fsw), burst mode frequency (fburst), and on-time (ton).
Load Transient Response
Figures 17 and 18 illustrate the load transient response. They show the output voltage (VOUT) ripple when the output current (IOUT) is stepped between 0.1 A and 1 A, with slew rates of 0.5 A/μs. The peak-to-peak output voltage ripple is measured.
Output Voltage Ripple
Figures 19 through 22 display the output voltage (VOUT) ripple under various load currents (1 A, 0.5 A, 0.1 A, 0.0 A) at an input voltage of 25 V. The VDRV(t) waveform is also shown.
Drain-Source Voltage
Figures 23 and 24 show the drain-source voltage (VDS) waveforms during operation at different input voltages and load conditions.
Standby Data
Table 1. No-Load Input Power When the IC is Self-Supplied 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 |
| 45 | 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
Figures 25, 26, and 27 present efficiency curves versus input voltage for load currents of 1 A, 0.5 A, and 0.1 A, respectively. These graphs compare the efficiency for three different VCC supply configurations: Self-supply, VCC = Vaux, and VCC = Vin.
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 ΚΩ | 1% | 2512 | Generic | |
| R2, R13 | 2 | Resistor | 40 ΜΩ | 1% | 2512 | Vishay | WSL2512R0400FEA |
| R3 | 1 | Resistor | 845 Ω | 1% | 0805 | Generic | |
| R4 | 1 | Resistor | 1.5 ΚΩ | 1% | 0805 | Generic | |
| R5 | 1 | Resistor | 68 ΚΩ | 1% | 0805 | Generic | |
| R6, R11, R17 | 3 | Resistor | 10 ΚΩ | 1% | 0805 | Generic | |
| R7 | 1 | Resistor | 133 ΚΩ | 1% | 0805 | Generic | |
| R8, R18, R19 | 0 | Resistor | NU | 1% | 0805 | Generic | |
| R9 | 1 | Resistor | 560 Ω | 1% | 0805 | Generic | |
| R10, R16 | 2 | Resistor | 10 Ω | 1% | 0805 | Generic | |
| R12, R14 | 2 | Resistor | 100 Ω/0.5 W | 1% | 0805 | Generic | |
| R15 | 1 | Resistor | 38 Ω | 1% | 0805 | Generic | |
| R20 | 1 | Resistor | 2.2 Ω | 1% | 0805 | Generic | |
| R21, R100 | 2 | Resistor | 0 Ω | 1% | 0805 | Generic | |
| R22 | 1 | Resistor | 1Ω | 1% | 0805 | Generic | |
| R23 | 1 | Resistor | 33 Ω | 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 |
Legal Information and Disclaimers
onsemi, onsemi., and other names, marks, and brands are registered trademarks of Semiconductor Components Industries, LLC. This evaluation board/kit is intended for research, development, demonstration, and evaluation purposes only and is not a finished product available for sale to consumers. It is designed for use in laboratory/development areas by trained personnel familiar with electrical/mechanical components and systems. The user assumes full responsibility for proper and safe handling. Any other use, resale, or redistribution is strictly prohibited.
The board is provided "as is" without warranties. onsemi disclaims all representations and warranties, including those of merchantability, fitness for a particular purpose, and non-infringement. onsemi reserves the right to make changes without notice.
Users are responsible for determining the board's suitability for their intended use and for testing and validating their designs. Technical information provided by onsemi does not constitute a warranty.
onsemi products are not designed or authorized for life support systems, FDA Class 3 medical devices, or devices intended for implantation. Users agree to indemnify onsemi against liabilities arising from unauthorized use.
This evaluation board/kit may not meet EU directives regarding electromagnetic compatibility, RoHS, WEEE, FCC, CE, or UL. It may generate, use, or radiate radio frequency energy and may cause interference with radio communications, for which the user is responsible to take corrective measures.
onsemi does not convey any license under its patent rights. onsemi's liability is limited to the purchase price of the board and excludes special, consequential, incidental, indirect, or punitive damages.
Additional Information
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