Power Supply For Ultra High-Fidelity Audio Amplifier LME49810, LME49811, LME49830

This application note will cover the design of a ±72V unregulated power supply designed specifically for the LME49810, LME49811 and LME49830 high-fidelity audio amplifier modules. The output power of the modules are approximately 220W to 250W into 8Ω and 350W to 400W into 4Ω. Complete documentation for the amplifier modules can be found in the documents listed below. AN-1625 LME49810TB Ultra-High Fidelity, High-Power Amplifier Reference Design AN-1850 LME49830TB Ultra-High Fidelity, High-Power Amplifier Reference Design Although the power supply design is specific to the amplifier modules the concepts and circuit design may be used for any power supply purpose. The power supply is an unregulated design with an option to allow connection to either 120V or 240V mains. The design uses toroidal transformers, a fully integrated bridge, and various rail capacitors for ripple voltage reduction, noise suppression, and to act as high current reservoirs. Additional circuitry to control inrush current on power up and power up/ down Mute control are also included. A complete schematic, PCB views, and Bill of Materials are provided for the power supply design.

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900W PFC Circuit

This PFC circuit is designed using Power Integration’s HiperPFS PFS729EG integrated PFC controller. This design is rated for a continuous output power of 900 W and provides a regulated output voltage of 380 VDC nominal maintaining a high input power factor and overall efficiency from light load to full load.

4.1 Input EMI Filtering and Rectifier

Fuse F1 provides protection to the circuit and isolates it from the AC supply in case of a fault. Diode bridge BR1 rectifies the AC input. Capacitors C1, C2, C3, and C4 together with inductors L1, L2 and L3 form the EMI filter reducing the common mode and differential mode noise. Resistors R1, R2 and CAPZero, IC U1 are required to discharge the EMI filter capacitors once the circuit is disconnected. High frequency decoupling capacitor C5 after the bridge reduces the loop area of the high frequency loop and helps reduce the noise coupled into the input wires. Resistor R3 connected in series with capacitor C1 provides damping. Metal Oxide Varistor RV1 is placed across AC power lines to provide differential mode surge protection.

4.2 PFS729EG Boost Converter

The boost converter stage consists of inductor L4, diode rectifier D2 and the PFS729EG IC U2. This converter stage works as a variable frequency continuous conduction mode boost converter and controls the input current of the power supply while simultaneously regulating the output DC voltage. Diode D1 prevents a resonant buildup of output voltage at start-up by bypassing inductor L4 while simultaneously charging output capacitor C13. Thermistor RT1 limits the inrush current of the circuit at start-up. In higher performance (efficiency) power supplies, this thermistor is shorted after start-up using a relay. Efficiency measurements should therefore be taken with RT1 shorted to obtain maximumefficiency data. Capacitors C11 and C12 are used for reducing the loop length and area of the output circuit to reduce EMI and overshoot of the voltage across the drain and source of the MOSFET inside U2 at each switching instant.

4.3 Bias Supply Regulator

The PFS729EG IC requires a regulated supply of 12 V for operation. Should this supply exceed 13.4 V, the IC could be damaged. Resistors R7, R8, R9, Zener diode VR1, and transistor Q1 form a shunt regulator that prevents the supply voltage to IC U2 from exceeding 12 V. Capacitors C6, C7 and C8 filter the supply voltage to ensure reliable operation of IC U2. Diode D3 protects the circuit against accidental reversal of polarity of the bias supply.

4.4 Input Feed Forward Sense Circuit

The input voltage of the power supply is sensed by the IC U2 using resistors R4, R5 and R6. The capacitor C9 filters any noise on this signal.

 

Circuit From www.powerint.com

65W Laptop Power Adapter Circuit Diagram

The schematic in Figure 1 depicts a notebook adapter power supply employing the Power Integrations® TOPSwitch®-HX TOP258EN off-line switcher in a fl yback configuration. This power supply operates from a universal input to provide a 19 V, 65  output capable of operation in a sealed enclosure at an ambient temperature of up to 40 °C. The TOP258EN (U1) has an integrated 700 V MOSFET and a multi-mode controller to regulate output by adjusting the MOSFET duty cycles, in response to current fed into the Control (C) pin. The Eco Smart® function in U1 provides constant efficiency over an entire load range. Using a proprietary multi-cycle-modulation (MCM) function eliminates the need for special operating modes triggered at specific  loads and operating conditions, optimizing performance for existing and emerging energy-efficiency regulations. Fuse F1 provides protection to the rest of the circuit from catastrophic failures. Common-mode inductors L3 and L4 provide line fi ltering. X-capacitor C1 provides differential fi ltering, and resistors R1 and R2 provide safety from shock upon AC removal. Bridge rectifi er D1 rectifies the AC input, and bulk capacitor C2 fi lters the DC. Y-capacitor C11, connected between the transformer (T1) primary and secondary side provides common-mode filtering.

 

 

 

Circuit From www.powerint.com

NTC For Power Supply

NTC Thermistor devices are made of a specially formulated metal oxide ceramic material which is capable of suppressing high current surges. TP type NTC devices, being of relatively high resistance, shall limit the inrush current for 1~2 seconds during which time the device decreases in resistance substantially to a point where its voltage drop is negligible. The devices are especially useful in power supplies (see FigA) because of the extremely low impedance of the capacitor being charged, of which the bridge is usually subjected to an exceedingly high current surge at turn-on point. NTC Thermistor of Inrush Current Limiting High inrush

As shown in Fig. , the current surge can be eliminated by Placing a NTC thermistor in series with a filament string. Yet, if the resistance of one NTC thermistor does not provide sufficient inrush current limiting functions for your application, two or more may be used in series or in separate legs of the supply circuit (Fig.A). Be noticed, the thermistor cannot be used in parallel since one unit will tend to conduct nearly all the current available. Thus, thermistor may be used in the AC (point A1 or A2) or the DC(point D1 or D2) locations in the circuit.(See Fig. A) The resistance of NTC thermistor is designed higher than the total resistance of filaments when the circuit is turned on. As current begins flowing, the thermistor shall immediately self-heat . Then, in 1~2 seconds, its resistance will be reduced to a minimum and become insignificant to the total resistance of a circuit. With the same concept, current surges in electric motors can be held to minimum. Fig. C shows a typical DC motor s turn on surge before and after the application of a TP type thermistor to the circuit.

 

Details From WMEC Application