Charger with boundary mode control

Abstract

The invention discloses a charging equipment provided with boundary mode control, comprising a transformer, a power switch, a detection circuit and a pulse width modulation controller; the power switch is connected with one end of a primary coil of the transformer in series; the detection circuit is electrically connected with the primary coil and the power switch for detecting the resonance of parasitic components of the power switch when the power switch is cut off, so as to provide a detection signal for the boundary control, the detection circuit includes an electric current mirror and a capacitor, the power source end of the electric current mirror is electrically connected with the other end of the primary coil, and one end of the capacitor is electrically connected with the power switch, the other end of the capacitor is electrically connected with the input end of the electric current mirror; and the pulse width modulation controller is used for generating a pulse width modulation signal to switch the power switch and leading the power switch to be conducted according to the detection signal.

Description

technical field [0001] The present invention relates to a charging device, in particular to a charging device with boundary mode control. Background technique [0002] In the known technology, there are generally two methods for charging control of a charging device. They are continuous conduction current mode control (Continuous Conduction Current Mode; CCM) and discontinuous conduction current mode control (Discontinuous Conduction Current Mode; DCM). [0003] figure 1 Shown is a charging device 10 with continuous conduction current mode (CCM) control in the known technology. When the power switch 105 is turned on, the primary coil current Ip of the transformer 101 will rise, and after the Ip current rises to the peak current setting value (in The peak current setting terminal 111 of the pulse width modulation controller 110 is set), and the power switch 105 will be turned off. [0004] After the power switch 105 is turned off, the secondary side current Is gradually de...

AI Technical Summary

Problems solved by technology

However, the charging device 30 still has the following disadvantages, for example: (1) when the power switch 305 is cut off, and the secondary side current Is of the transformer 301 drops to zero, the drain voltage Vsw of the power switch 305 drops to one due to resonance. When the reference voltage Vref is reached, the power switch 305 is turned on again. At this time, the ratio of the blank time Tb to the off-time Toff of the power switch 305 will be longer as the Vsw voltage is higher (please refer to Figure 4 ), because during the blank time Tb, the charging device 30 does not transmit the energy of the input terminal voltage Vin to the output terminal capacitor Co, so the overall charging time is longer and the charging efficiency is poor; (2) due to the addition of the blank time, the power The cut-off time Toff of the switch is relatively long and the switching frequency is low, so a larger transformer must be used; (3) Due to the low switching frequency, a larger input capacitor Cin is required to achieve a smaller average charging current Iin ripple ; (4) During the charging process, as the output terminal Vout voltage gets higher, the average charging current Iin cannot maintain a fixed value and will gradually decrease

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