| 摘要 |
Primary side sensing is used to estimate and to regulate the output current of a switch mode power supply (SMPS) comprising a transformer 21, a primary winding connected to switch 31 and a secondary winding connected to an output. An averaged primary current signal CS, a signal T0 representing the transformer charging time and a signal T1 representing the transformer discharge time are used to estimate output current OC, and to regulate it from an error signal ERR that is derived from a desired output current OCT. The sensed primary current CS, the charge signal T0 and the discharge signal T1 may be averaged over a switching cycle of the SMPS by low pass filters (figs 6-8, 12-14). The output current may be calculated by dividing the average primary current, multiplied by the discharge signal, by the charge signal, by means of either a delta-sigma circuit (fig 9) or a trans-linear circuit (fig 10). The charge time (fig 4, T0) may be the on time of switch 31 and the discharge time (fig 4, T1), when current is flowing through the secondary, may be found by comparing a sensed voltage VS from an auxiliary winding of transformer 21, or from the primary winding (fig 2). with the output voltage OV derived by an output voltage model (fig 5, OVM). |
