Dr. Fuld

Dr. Fuld Ing.-GmbH
Frankfutrer Landstr. 112

D-61352 Bad Homburg

Fon: + 49 6172 928 928
Fax: + 49 6172 928 927

gf@fuld.de

Synchronous Rectification

For synchronous rectification MOSFETs, operating in reverse direction and controlled by an adapted logic circuit, are used instead of (Schottky-) diodes. Since MOSFETs exhibit a purely Ohm's conducting behavior contrary to diodes, thereby rectifier switches with substantially smaller conducting losses can be realized.

Circuit diagram
 
 
 
 
 
 

With 5V thereby an improvement of the efficiency of up to 10%-points can be achieved. This relieved not only the solution of the heat dissipation problems, but is also in the long term view a more economical solution

Example

Data: 5V/10A-Output

 Classical solution

 Synchronous rectifier

Part Number

 MBR1535CT

 2 x SUM85N03-08P

 2x15A/ 35V Schottky

 7,5 mOhm 30V MOSFET

 Price

0,58 €

1,88 €

 Losses

 6,0

 1,5

 Cooler

 SK409 25,4

 

 Price

1,10 €

 

 IC for control

 

 STSR2

 Price

 

1,21 €

 Investments

1,68 €

3,09 €

 Electricity tariff/ kWh

0,10 €

0,10 €

 Actual working time p.a.

 8000

 8000

 Cost of electricity over 3 years for energy dissipation

14,40 €

3,60 €

 Total costs

16,08 €

6,69 €

 Advantage synchronous rectification

   

9,39 €

Remark: At higher currents the advantages are still more substantial, since the expenditure for the control is nearly independent from the output current.