The MAX15005 can be used for an Isolated Boost, SEPIC or Flyback Converter to provide in this instance an isolated 96V and 300mA output. The desired input voltage range is 12V-36V and an Industrial temperature rating of -40'C to 125'C is required.
The design requires 1500Vrms Galvanic Isolation between the input voltage source and isolated Converter's output to be housed in the customer's Industrial and Railway electrical control panels.
Lastly, advice for DC-DC converter Topology selection and alternate controllers is given.
The MAX15005 Power Supply Controller can be utilized for designing a Boost, Flyback or SEPIC DC-DC Converter. The controller operates within the required input voltage range and is Industrial temperature rated, -40'C to 125'C. However, Galvanic Isolation must be addressed first before selecting a DC-DC Converter Topology.
Galvanic Isolation techniques are used in electrical circuits to prevent current flow between two isolated electrical circuits.No direct electrical conduction path is allowed between isolated circuits. Galvanic Isolation is typically required for electrical safety, to protect circuits from high common-mode transients, faults and ground loops
encountered in electrical systems.
The MAX15005 Boost or Step-Up DC-DC converter as shown below (MAX15005 IC data sheet, page 25, Figure 8) allows current to flow between the input and output circuits. Thus a Boost or Step-Up DC-DC converter does not provide Galvanic Isolation between the VIN and VOUT circuits.
On the positive VIN power supply rail, there is a DC current conduction path at input capacitor C1, through power inductor L1 and then through power diode D1 to output capacitor C6 at the VOUT power supply rail.
The VIN PGND power supply ground has a direct connect to capacitor C1 and the VOUT power supply ground at capacitor C6, PGND. The VIN return current flows through this path. Additionally the MAX15005 controller SGND and PGND grounds are connected together at capacitor C10.
Again, a Boost or Step-Up DC-DC converter as shown below does NOT provide Galvanic Isolation between the VIN and VOUT circuits.
The SEPIC converter as shown below (MAX15005 IC data sheet, page 22, Figure 6) allows current to flow between the input and output circuits. Thus a SEPIC DC-DC converter in this configuration does NOT provide Galvanic Isolation between the VIN and VOUT circuits.
On the positive VIN power supply rail, during the 1st switching cycle power MOSFET is ON, there is a DC current conduction path at the input capacitor C7, through coupled inductor L11 and then through the power MOSFET and sense resistor RS to PGND. Additionally coupled inductor L22 sources current from PGND to Coupling capacitors C1-C3 connected to PGND. During this cycle, D2 is OFF and output capacitors C4-C6 supply current to the VOUT load connected to PGND.
During the second switching cycle, the MOSFET is OFF, there is a DC current conduction path from input capacitor C7, through coupled inductor L11, then in to Coupling capacitors C1-C3 feeding current into power diode D2 and Output capacitors C4-C6 at the VOUT power supply rail.
The VIN PGND power supply ground has a direct connect to input capacitor C7 and the VOUT power supply ground at output capacitors C4-C6, PGND. Additionally the MAX15005 controller SGND and PGND grounds are connected together at capacitor Cvcc.
Again, a SEPIC DC-DC converter in this configuration does NOT provide Galvanic Isolation between the VIN and VOUT circuits.
For a Galvanically Isolated DC-DC converter, the isolated Flyback DC-DC converter as shown below (MAX17596 IC data sheet, page 19, Figure 10) provides isolation between the VIN input and VOUT output circuits.
On the positive VIN power supply rail, there is a DC current conduction path at input capacitors C1-C2, through isolation Transformer T1 primary side winding and then through power MOSFET N1 and sense resistor R9 to PGND during the 1st switching cycle when power MOSFET is ON.
During this switching cycle, on the isolated secondary side, power Diode D2 is OFF and the output capacitors supply current to the VOUT power supply rail.
During the second switching cycle, power MOSFET N1 is OFF. On the isolated secondary side current flows from Transformer T1 secondary side winding
into diode D2 and to Output capacitors C9-C13 at the VOUT power supply rail.
The VIN PGND power supply ground has a direct connection to input capacitors C1-C2 and all primary side components only. Additionally the MAX17596 controller primary side SGND and PGND grounds are connected together on the primary side only.
On the secondary side, the VOUT power supply ground GND0 has a direct connection to output capacitors C9-C13 and all secondary side components only.
Optical Isolator U2 provides Galvanic Isolation for transferring the voltage regulation signal from the secondary side to the primary side for control. Transformer T1 and Optical Isolator U2 isolation ratings determine the primary to secondary side circuits' isolation rating. Thus a Flyback DC-DC converter as shown below provides Galvanic Isolation between the VIN and VOUT circuits.
The MAX15005A/B or MAX15004A/B could also be utilized as the Flyback controller for the isolated Flyback circuit.
The MAX17596 and MAX15005 Power Supply Controllers are Industrial temperature rated, -40'C to 125'C and operate within the customers required input voltage range of 12V-36V.
Lastly, one must select a Transformer T1 and Optical Isolator ratings of at least 1500Vrms or more to meet the required isolation specification.