Multi-output flyback power supply circuit design for audio amplifier

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Summary:

working principle

The universal input power supply has multiple outputs: ±26 VDC, ±15 VDC, and +5 VDC. The ±26 V output provides a minimum output current of 2.42 A peak (affected by temperature) and a continuous output current of 1.45 A. In addition, not only voltage regulation, but also more important transient response, is excellent over the entire load range (no load to full load).

The controller in U1 skips the switching cycle and regulates the output voltage based on the current fed to its EN/UV pin. When the current flowing from this pin exceeds 240 μA, a low logic level (disable) is generated. At the beginning of each cycle, the EN/UV pin state is sampled; if high, the power MOSFET is turned on (enabled) during that cycle, otherwise the power MOSFET will remain off (disabled). At startup, the switch is inhibited until the input voltage exceeds the undervoltage threshold when the current flowing into the EN/UV pin is greater than 25 μA.

design feature

• Can effectively replace the linear transformer power supply used in home audio systems
• Significantly reduce the weight of the product, thus saving the cost of the audio chassis
• High precision cross-regulation of two main outputs in a flyback topology using a patented magnetic amplifier (mag amp) method
• Small component count, compact and lightweight
• High energy efficiency
• More than 82% efficiency at full load
• No-load power consumption less than 800 mW at 265 V AC input
• Reduces the use of heat sinks and eliminates the need for independent standby power
• Excellent transient response improves audio quality
• Integrated frequency modulation with a simple EMI filter enables the design to meet CISPR-22/EN55022B conducted EMI requirements (see Figure 2)
• Integrated safety and reliability:
• Precise, auto-recovery and hysteretic shutdown with hysteresis to keep PCB temperature within safe conditions under all conditions
• Entering the latched shutdown state when the output short circuit and the feedback loop are open loop

Circuit design of 75W continuous output, 126W peak audio amplifier power supply

See the PDF document for details (click on the PDF file to download)