PN junction diode

screw-inpowervoltage

Backup power system sometimes require OR-ing of batteries. For example to get the system online while the main battery is discharged. When currents are low, this is done easily using a simple diode. However, when currents become more significant, power dissipation in a diode quickly increases to unacceptable levels because of the unavoidable forward voltage of the diode. Not to mention that this forward voltage wastes between 5 and 10 percent of the available power (from a 12V battery). For this reason, this active 'ideal' diode block was designed. The diode is replaced with a high current mosfet. Without working voltage, this mosfet behaves as a regular diode. After applying voltage, the mosfet driver is activated. The driver enables the mosfet and regulates the forward voltage to 30mV (30 times less than a typical normal diode), or to the lowest voltage that can be archieved giving the current draw and the Rds resistance of the mosfet. This resistance causes a forward voltage of about 1mV per Amp. Performance: To put this in context; the 16mm² wires and their terminals in the 60A test setup cause a voltage drop of 85 and 95mV respectively! The voltage drop accross the diode, measured on the terminal screws was 73mV. Specifications: Reverse voltage rating 40V Current rating 600A Package SOT-227 (footprint 25x38mm) M4 screw terminals suitable for 4mm and 5mm ring terminals Electrical isolation to metal base 2500VAC, 1 minute Thermal resistance junction to metal case (RθJC) 0.21°C/W () * Thermal resistance junction to ambient (RθJA) ~20°C/W () * Maximum junction temperature 175°C Minimum working voltage 8VDC Drain-source resistance (Rds) 0.001Ω