3W Primary-Side Transformer H-Bridge Driver for Isolated Supplies


The MAX256 is an integrated primary-side controller and H-bridge driver for isolated power-supply circuits. The device contains an on-board oscillator, protection circuitry and internal FET drivers to provide up to 3W of power to the primary winding of a transformer. The MAX256 can be operated using the internal programmable oscillator or can be driven by an external clock for improved EMI performance. Regardless of the clock source being used, an internal flip-flop stage guarantees a fixed 50% duty cycle to prevent DC current flow in the transformer.

The MAX256 operates from a single-supply voltage of +5V or +3.3V, and includes undervoltage lockout for controlled startup. The device prevents cross-conduction of the H-bridge MOSFETs by implementing break-before-make switching. Thermal shutdown circuitry provides additional protection against damage due to overtemperature conditions.

The MAX256 is available in the 8-pin thermally-enhanced SO package. The device is specified for the automotive (-40°C to +125°C) temperature range.

MAX256: Typical Operating Circuit MAX256: Typical Operating Circuit Enlarge+

Key Features

  • Simple, Flexible Design Provides Up to 3W to the Transformer in Isolated Power Supplies
    • Single Supply +5V or +3.3V Operation
    • Internal Resistor-Programmable Oscillator Mode
    • External Clock Mode with Watchdog
    • Disable Mode
  • Integrated System Protection
    • Undervoltage Lockout
    • Thermal Shutdown
  • Saves Space on Board
    • 8-Pin Thermally-Enhanced SO Package


  • Industrial Process Control
  • Isolated Communications Links
  • Isolated Power Supplies
  • Medical Equipment
  • Telecommunications
Part Number VIN
Driver Output Resistance
Topology Freq.
Package/Pins Oper. Temp.
min max max max See Notes
MAX256  3 5.5 1 1 Full-Bridge 1000 1
-40 to +125 $3.34 @1k
See All Transformer Drivers (6)
Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

MAX256EVKIT: MAX256 Evaluation Kit
MAXSANTAFEEVSYS: Evaluation Kit for the MAXREFDES5 4-Channel Analog Front End

Related Resources