Isolated Power Supply with 24V Input and Dual 15V Output

This isolated power supply features the SN6507 chip, a push-pull isolation transformer driver, which provides a reliable and efficient power conversion solution. The power supply comprises a transformer, rectifier circuit, and isolation transformer T1, which separates the input and isolated output, ensuring electrical isolation and preventing high voltages and noise from interfering with or damaging sensitive circuitry.

The SN6507 chip generates complementary output signals (SW1 and SW2), which are ground-referenced, N-channel power switches that drive the primary side of the center-tapped transformer. The secondary side of the transformer has its center tap referenced to an isolated ground plane, and the complementary outputs are rectified through a four-diode bridge. The break-before-make feature of the two driver outputs from the SN6507 ensures that only one of the primary-side transformer windings is driven at a time, preventing simultaneous conduction and minimizing electromagnetic interference (EMI).

After rectification, the DC voltage is smoothed and routed to an unregulated dual output, capable of powering external loads up to 500 mA. This isolated power supply is designed to provide a stable and reliable power source for sensitive electronic circuits, ensuring optimal performance and minimizing the risk of electrical noise and interference damage. Ferrite beads L1 and L2 are provided to reduce emissions when power supply outputs are connected to long cables or have high ringing. Optional secondary-side snubber circuit built using R8, R9, C9, C10 helps minimize electromagnetic emissions. These components are optional so they may be replaced with other components or removed.

An RC snubber circuit of 100 Ω, 62pF is populated on R12, C15, and R13, C16 by default to help minimize electromagnetic emissions. These components are optional so that they may be replaced with other components or removed from the PCB and excluded from designs using the SN6507 device.

Soft Start and Over Current Limit

• Resistor R2: R_ilim is used to adjust the over-current protection limit of SN6507
• Capacitor C7: C_SS is used to adjust the soft start time of SN6507 during power-up. The chip features a soft start and current limit.

Output: Power Supply provides unregulated Dual outputs, without load +/-18V, With Load +/-15V DC, 250mA+250mA=500mA from 24V DC Input. The output varies with the input power supply voltage

Features

• Output +/-18V (Dual 18V) without Load, (+/-15V Approx. With Full Load), Unregulated
• Output Load Current 500mA (250mA+250mA)
• Operating Frequency 1Mhz
• On Board Power LED Input Side
• 2 Pin Header Connector for Power Input
• 3 Pin Header Connector for Dual Power Output
• Compact SIP Type PCB fits in a small area
• PCB Dimensions 34.93 x 13.65 mm

The SN6507 is a high voltage, high-frequency push-pull transformer driver providing isolated power in a small solution size. The device comes with the push-pull topology’s benefits of simplicity, low EMI, and flux cancellation to prevent transformer saturation. Further space savings are achieved through duty cycle control, which reduces component count for wide-input ranges, and by selecting a high switching frequency, reducing the size of the transformer. The device integrates a controller and two 0.5-A NMOS power switches that switch out of phase. Its input operating range is programmed with precision undervoltage lockouts. The device is protected from fault conditions by over-current protection (OCP), adjustable under-voltage lockout (UVLO), over-voltage lockout (OVLO), thermal shutdown (TSD), and break-before-make circuitry. The programmable Soft Start (SS) minimizes inrush currents and provides power supply sequencing for critical power-up requirements. Spread Spectrum Clocking (SSC) and pin-configurable Slew Rate Control (SRC) further reduce radiated and conducted emissions for ultra-low EMI requirements.

Connections

• CN1 Power Output: Pin 1 = +V DC Output, Pin 2 = GND, Pin 3 = -V DC Output
• CN2 Power Input: Pin 1 = +Input 24V DC, Pin 2 = GND
• D5: Power LED

Schematic

Parts List

Connections

Gerber View

Photos

SN6507 Datasheet

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