High Efficiency, Ultra-Compact Flyback Power Supplies Utilizing GaN Chipsets

A new chipset is now on the market, combining a flyback IC solution with a durable 750V Gallium Nitride (GaN) primary-side switch and an innovative high-frequency active clamp Tablets and laptops are designed with new ultra-compact chargers rated up to 110W. This chipset from Power IntegraTIons includes the InnoSwitch™ 4-CZ zero-voltage switching (ZVS) flyback controller with PowiGaN™ switches integrated inside and the ClampZero™ product family providing active clamping solutions.These new ICs can be used in designs with efficiencies up to 95% and at different input

By Chris Lee, Director of Product Marketing, Power IntegraTIons

A new chipset is now on the market, combining a flyback IC solution with a durable 750V Gallium Nitride (GaN) primary-side switch and an innovative high-frequency active clamp Tablets and laptops are designed with new ultra-compact chargers rated up to 110W. This chipset from Power IntegraTIons includes the InnoSwitch™ 4-CZ zero-voltage switching (ZVS) flyback controller with PowiGaN™ switches integrated inside and the ClampZero™ product family providing active clamping solutions. These new ICs can be used to design flyback power supplies with up to 95% efficiency and constant input voltage conditions.

This InnoSwitch4-CZ/ClampZero combination brings refreshing new performance to flyback power supply designs. Due to the primary leakage inductance in the transformer, an active clamp circuit is required on the primary side. When the primary-side switch is turned off, leakage inductance commutation can cause voltage overshoot, which can damage the MOSFET. A common solution is to use passive resistor-capacitor-diode (RCD) clamps to protect the MOSFETs (see Figure 1). The clamp transfers leakage inductance energy into the clamp capacitor and dissipates it as heat in the resistor. The RCD clamp reduces flyback efficiency but provides protection for the MOSFET.

High Efficiency, Ultra-Compact Flyback Power Supplies Utilizing GaN Chipsets
Figure 1. Passive primary clamp RCD solutions dissipate significant amounts of heat and limit

Efficiency of Flyback Power Supplies

During each switching cycle, the energy in the clamp is lost. This forces designers to limit the maximum switching frequency, which in turn requires the use of larger transformers. Therefore, passive clamping solutions can reduce flyback efficiency or result in larger and/or hotter power supplies. A more efficient approach is to replace the passive RCD network with an active clamp.

Active clamp

Active clamping does not dissipate energy, but instead recycles leakage inductance energy, increasing efficiency and reducing heat generation. In an active clamp design, the resistor in the RCD snubber is replaced by a switch. If ClampZero is used, the switch is a PowiGaN device (see Figure 2). After the primary switch is turned off, the secondary control instructs the ClampZero switch to turn on and transfers the clamp capacitor energy storage to the secondary before the primary switch turns on. The recirculation clamp circuit commutates the leakage inductance current and also ensures that the voltage on the primary switch is zero (ZVS) before it turns on.

High Efficiency, Ultra-Compact Flyback Power Supplies Utilizing GaN Chipsets
Figure 2. InnoSwitch4-CZ/ClampZero flyback scheme

In a traditional active-clamp design, the primary MOSFET and active-clamp switch operate in a complementary fashion (hence these clamps are called “complementary-mode active-clamp” circuits). In this working mode, the converter can only work in discontinuous conduction mode or critical conduction mode, and cannot work in continuous conduction mode. This presents a challenge for designers when designs requiring a wide output voltage range, such as USB PD and PPS chargers, result in designs that must conduct very discontinuously at high input voltages. However, the InnoSwitch4-CZ/ClampZero chipset overcomes this limitation.

InnoSwith4-CZ and ClampZero

The InnoSwitch4-CZ and ClampZero IC chipsets employ a complex, asymmetric, non-complementary active-clamp control method to achieve intelligent zero-voltage switching, while supporting both discontinuous and continuous conduction modes of operation, increasing design flexibility and enabling Maximum efficiency under working conditions. The new flyback switch IC has excellent constant voltage/constant current accuracy, is not affected by the tolerance of peripheral components, and provides input voltage detection and other safety and protection functions, its no-load power consumption is less than 20mW.

Housed in a thin InSOP™-24D package, the InnoSwitch4-CZ product family integrates a 750V switch, primary and secondary controllers, ClampZero interface, synchronous rectification, and safety-compliant feedback circuitry. Steady-state full-load switching frequencies of up to 140kHz reduce transformer size, further increasing power density.

Design example

Designers can use the InnoSwitch4-CZ and ClampZero ICs with Power IntegraTIons’ previous MinE-CAP™ IC products to design ultra-compact flyback power supplies. The MinE-CAP is a natural complement to the InnoSwitch4-CZ and ClampZero ICs; it significantly reduces the size of the input bulk capacitors without compromising output ripple, operating efficiency and requiring no transformer redesign.

MinE-CAP enables equal or greater overall power supply size reduction compared to traditional technologies such as very high switching frequency operation, while avoiding complex EMI filtering and increased transformer/clamping dissipation associated with very high frequency designs challenge. MinE-CAP also accurately manages inrush current at AC power-up, eliminating the need for power-hungry NTCs or large slow-blow fuses.

The DER-928 design example from Power IntegraTIons is an ultra-compact 60W USB PD 3.0 charger for cell phones and laptops. The design features are as follows:

・Used InnoSwitch4-CZ active clamp flyback switch IC with high voltage PowiGaN switch (INN4073C)
・Use ClampZero active clamp IC (CZ1062M)
・Using MinE-CAP large capacitance miniaturized IC (MIN1072M)
・Input: 90VAC – 265VAC
・USB-C PD output: 5V/3A; 9V/3A; 15V/3A; 20V/3A

High Efficiency, Ultra-Compact Flyback Power Supplies Utilizing GaN Chipsets
Figure 3. DER-928 Design Example: 60W Ultra-Small USB PD Charger Using InnoSwitch4-CZ, ClampZero, and MinE-CAP Chipsets, 24.4cm3 (44mm2 x 12.6mm Height)

In the above design, replacing the bulk 100µF capacitor with a 130µF input capacitor increases the peak power to 90W. Other performance characteristics include:

・Easy compliance with DOE6 and CoC v5 2016 energy efficiency standards
・Provide output overvoltage and overcurrent protection
・Internally integrated thermal shutdown protection feature
・No-load input power < 60mW, microcontroller power consumption is 20mW
・Compact design with high power density: 30.3W/in3 without housing (ie, 60W/1.77in X 1.77in X 0.63in)

The chipsets included in the InnoSwitch4-CZ/ClampZero solution deliver 65W to 110W of output power (see Table 1). They are available in adapter or open-frame designs, support 85-264VAC input voltage, and can also support 385VDC operation by adding power factor correction (PFC) front-end circuitry.

High Efficiency, Ultra-Compact Flyback Power Supplies Utilizing GaN Chipsets
Table 1. InnoSwitch4-CZ and ClampZero Product Family

Summarize

Power Integrations’ InnoSwitch4-CZ/ClampZero chipset enables designers to design ultra-high-density chargers up to 110W for cell phones, tablets and notebooks that were previously unattainable. The InnoSwitch4-CZ IC provides variable output voltage and constant current characteristics, making it ideal for high-efficiency compact USB-PD adapters and high-efficiency CV/CC power supplies. While providing safety and protection functions such as input voltage detection, the no-load power consumption is less than 30mW, and can provide up to 95%.

The Links:   LB104V03-TD01 G150XTN060