April 21, 2008

FMKS Series Developed
Fast-recovery rectifier diodes for thermal protection of SW power supplies for various devices (with built-in SBD for temperature detection)
Eliminates need for a heat-sensitive element such as a thermistor

Sanken Electric Co., Ltd. has developed the FMKS Series of fast-recovery rectifier diodes incorporating a Schottky barrier diode (SBD) for temperature detection. The FMKS Series are to be used for thermal protection of switching power supplies for various appliances (withstand voltage: 200 V; 3 currents: 5 A/10 A/15 A; package: TO220F, circuit patent pending). Sanken will start shipping samples at the end of April. Shipment of mass-production units will start at the beginning of May 2008 with 50k units/month, ramping up to 500k units/month by the beginning of 2009. The tax-excluded sample price is 150 yen for the 5 A model (FMKS-2052), 190 yen for the 10 A model (FMKS-2102), and 230 yen for the 15 A model (FMKS-2152).
1. Development Background and Product Overview
  The power supplies of some audio equipment and printers are equipped with a thermal protection circuit for preventing breakdown due to overheating.
The method employed in most thermal protection circuits is to detect overheating with a heat-sensitive element such as a thermistor incorporated in the power supply, and to protect the power supply through feedback to the primary side.
When using this method, though, a time lag occurs by the time overheating is detected, making it difficult to track sudden temperature changes, and the heat-sensitive element must be attached in the proximity of heater elements ensuring adequate thermal coupling.
In response, Sanken Electric focused on the temperature characteristic of the SBD*, developing the FMKS Series that allows to detect directly the temperature of fast-recovery rectifier diodes (hereafter, FRD) and to utilize it for the thermal protection by forming the SBD on the chip of the FRD in the secondary side and by utilizing its temperature characteristic.
Use of the FMKS Series eliminates the need of heat-sensitive elements such as thermistors, allowing cost reductions as well as simplification of thermal protection circuit design. Further, through the use of a 1-chip configuration, the temperature of the FRD becomes the temperature of the SBD and is fed back as is, allowing direct temperature detection with high accuracy.

* Temperature characteristic of SBD: Characteristic whereby the reverse leak current increases at high temperatures.
Using the area in which reverse leak current IR changes linearly in relation to the temperature, the temperature detection by monitoring the IR temperature changes activates the protection circuit.
2. Major Applications
  Power supplies for equipment requiring thermal protection, such as audio equipment, printers, air conditioners, and AC adapters
3. Features
(1) Achieves high-accuracy temperature detection in real time and requires no need for consideration for the mounting place by combining an FRD for rectification and an SBD used for the temperature detection on one chip, and by enabling direct detection of the FRD temperature by the SBD.
(2) Current change characteristics are stable over a wide range, allowing to connect multiple detection circuits to the signal from one FMKS Series unit and enabling multistage detection of temperature.
(3) Whereas use of heat-sensitive elements such as thermistors requires the selection of parts suitable for the detection of particular temperatures, the FMKS Series enable adjustment of the detection temperature with just one resistor, for easy thermal protection circuit design.

TO220F full-mold package (dimensions of resin part: 10 × 17 × 4.2 mm)

4. Specifications
Parameter Symbol Rating Unit Condition
FMKS- 2052 FMKS- 2102 FMKS- 2152
FRD reverse voltage VR 200 200 200 V  
FRD forward current IF 5 10 15 A  
FRD reverse recovery time trr 35 max. 35 max. 35 max. ns  
SBD reverse leakage current IR 50max. 50 max. 50 max. μA VR=15V
SBD high-temperature reverse
leakage current
H·IR 1.90±0.7 1.90±0.7 1.90±0.7 mA VR=15V,
Tj=130° C
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