Switching mode power converter having secondary side bias generating and driving circuit to provide synchronous rectification and active clamp
A switched mode power converter includes a transformer having a primary winding, a secondary winding, and a bias winding. A primary side power switch is coupled to the primary winding and is adapted to periodically apply an input voltage to the primary winding. An output filter is operatively coupled to the secondary winding to provide an output voltage and output current. A forward synchronous rectification device is operatively coupled in series between the secondary winding and the output filter. A free-wheeling synchronous rectification device is operatively coupled in shunt with the secondary winding and the output filter. A control circuit is coupled to the bias winding and the forward and free-wheeling synchronous rectification devices. The control circuit includes a forward driving device adapted to couple an activation terminal of the forward synchronous rectification device to a first end of the secondary winding and a free-wheeling driving device adapted to couple an activation terminal of the free-wheeling synchronous rectification device to a second end of the secondary winding. The control circuit activates the forward and free-wheeling driving devices responsive to voltage on the bias winding.
1. A switched mode power converter, comprising:
a transformer having a primary winding, a secondary winding, and a bias winding;
a primary side power switch coupled to said primary winding and being adapted to periodically apply an input voltage to said primary winding;
an output filter operatively coupled to said secondary winding to provide an output voltage and output current;
a forward synchronous rectification device operatively coupled in series between said secondary winding and said output filter;
a free-wheeling synchronous rectification device operatively coupled in shunt with said secondary winding and said output filter; and
a control circuit coupled to said bias winding and said forward and free-wheeling synchronous rectification devices, said control circuit including a forward driving device adapted to couple an activation terminal of said forward synchronous rectification device to a first end of said secondary winding and a free-wheeling driving device adapted to couple an activation terminal of said free-wheeling synchronous rectification device to a second end of said secondary winding, said control circuit activating said forward and free-wheeling driving devices responsive to voltage on said bias winding.
2. The switched mode power converter of claim 1 , wherein said control circuit further comprises a first capacitor charged by said bias voltage during an on-state of said primary side power switch.
3. The switched mode power converter of claim 2 , wherein said control circuit further comprises a second capacitor receiving charge from said first capacitor during an off-state of said primary side power switch, voltage on said second capacitor activating said forward and free-wheeling driving devices.
4. The switched mode power converter of claim 3 , wherein said control circuit further comprises a clamping circuit adapted to regulate said voltage on said second capacitor.
5. The switched mode power converter of claim 1 , further comprising a reset capacitor operatively coupled to said primary winding, said reset capacitor being charged as current is withdrawn from said transformer during an off-state of said primary side power switch.
6. The switched mode power converter of claim 5 , wherein voltage on said reset capacitor is reflected in said voltage on said bias winding.
7. In a switched mode power converter comprising a transformer having a primary winding, a secondary winding, and a bias winding, a primary side power switch coupled to said primary winding and being adapted to periodically apply an input voltage to said primary winding, an output filter operatively coupled to said secondary winding to provide an output voltage and output current, a forward synchronous rectification device operatively coupled in series between said secondary winding and said output filter, and a free-wheeling synchronous rectification device operatively coupled in shunt with said secondary winding and said output filter, a control circuit comprises:
a forward driving device adapted to couple an activation terminal of said forward synchronous rectification device to a first end of said secondary winding;
a free-wheeling driving device adapted to couple an activation terminal of said free-wheeling synchronous rectification device to a second end of said secondary winding; and
a bias charge circuit adapted to provide a bias voltage to activate said forward and free-wheeling driving devices responsive to voltage on said bias winding.
8. The control circuit of claim 7 , wherein said bias charge circuit further comprises a first capacitor charged by said bias voltage during an on-state of said primary side power switch.
9. The control circuit of claim 8 , wherein said bias charge circuit further comprises a second capacitor receiving charge from said first capacitor during an off-state of said primary side power switch, voltage on said second capacitor activating said forward and free-wheeling driving devices.
10. The control circuit of claim 9 , wherein said bias charge circuit further comprises a clamping circuit adapted to regulate said voltage on said second capacitor.
11. A switched mode power converter, comprising:
a transformer having a primary winding, a secondary winding, and a bias winding;
a primary side power switch coupled to said primary winding and being adapted to periodically apply an input voltage to said primary winding;
an output filter operatively coupled to said secondary winding to provide an output voltage and output current;
a forward synchronous rectification device operatively coupled in series between said secondary winding and said output filter;
a free-wheeling synchronous rectification device operatively coupled in shunt with said secondary winding and said output filter;
a forward driving device adapted to couple an activation terminal of said forward synchronous rectification device to a first end of said secondary winding;
a free-wheeling driving device adapted to couple an activation terminal of said free-wheeling synchronous rectification device to a second end of said secondary winding; and
means for activating said forward and free-wheeling driving devices responsive to voltage on said bias winding.
12. The switched mode power converter of claim 11 , wherein said activating means further comprises a first capacitor charged by said bias voltage during an on-state of said primary side power switch.
13. The switched mode power converter of claim 12 , wherein said activating means further comprises a second capacitor receiving charge from said first capacitor during an off-state of said primary side power switch, voltage on said second capacitor activating said forward and free-wheeling driving devices.
14. The switched mode power converter of claim 13 , wherein said activating means further comprises a clamping circuit adapted to regulate said voltage on said second capacitor.
15. The switched mode power converter of claim 11 , further comprising a reset capacitor operatively coupled to said primary winding, said reset capacitor being charged as current is withdrawn from said transformer during an off-state of said primary side power switch.
16. The switched mode power converter of claim 15 , wherein voltage on said reset capacitor is reflected in said voltage on said bias winding.