| 摘要 |
This invention generally relates to synchronous rectifier controllers for an SMPS. One controller comprises: a sensor to sense a signal on a secondary side, to detect turn off of the switch; a charge source to, in response to a said detection, charge a control terminal of the rectifier to a voltage beyond a threshold voltage of the synchronous rectifier to allow the synchronous rectifier to conduct current of the secondary winding; and a linear amplifier having an output to sink current from the control terminal dependent on a difference between a voltage across the synchronous rectifier and an amplifier reference value, said voltage across the synchronous rectifier being a voltage across a controllable conduction path for current of the secondary winding, the linear amplifier to inhibit discharge of the control terminal from the voltage beyond the threshold voltage until the voltage across the synchronous rectifier reaches the amplifier reference value. |
| 主权项 |
1. A synchronous rectifier controller for a switched mode power supply (SMPS), comprising:
a synchronous rectifier, the SMPS having a power input, a switch, a transformer, an output capacitor and a power output, said transformer having a primary winding on a primary side of said SMPS coupled to said power input and said switch, and a secondary winding on a secondary side of said SMPS coupled to said power output and said output capacitor, said switch to switch power to said primary winding responsive to a drive signal, the SMPS further comprising sense circuitry on the primary side to sense a voltage on the secondary winding, the SMPS having a primary side sensing controller to control said drive signal according to at least the sensed voltage, the synchronous rectifier for blocking current flow from the output capacitor to the secondary winding, the synchronous rectifier controller comprising: a sensor to sense a signal on the secondary side, to thereby detect turn off of the switch; a charge source to, in response to a said detection, charge a control terminal of the synchronous rectifier to a voltage beyond a threshold voltage of the synchronous rectifier to allow the synchronous rectifier to conduct current of the secondary winding; and a linear amplifier having an output to sink current from the control terminal dependent on a difference between a voltage across the synchronous rectifier and an amplifier reference value, said voltage across the synchronous rectifier being a voltage across a controllable conduction path for current of the secondary winding, the linear amplifier thereby configured to inhibit discharge of the control terminal from the voltage beyond the threshold voltage until the voltage across the synchronous rectifier reaches the amplifier reference value. |
