Slope compensation

Analysis and design of slope compensation circuit in switching power supply

slope compensation

An adaptive slope compensation circuit for buck DC-DC converter
2007
The hypotensive type DC-DC Design of converter self-adjusting slope compensation circuit , Li Yanming , Come to Xinquan , Wang Hongyi - Microelectronics and computers , 2005

Peak current mode control and digital control have many advantages . therefore , It is an interesting method to combine these two technologies in a control structure . Based on microcontroller with on-chip comparator , This combination can be realized very easily . In order to eliminate the shortcomings of peak current mode control , Slope compensation must be added . This paper introduces the slope compensation realized on the microcontroller , This compensation does not use analog ramp signals , Instead, the required comparator off threshold is calculated in advance . Compared with traditional analog control , The adaptive algorithm can be used to maintain the optimal slope compensation in a wide working range . The problems arising in practice due to the peak of reverse recovery current and calculation time can be solved by simple measures . Experimental results verify the effectiveness of the proposed digital slope compensation .

Current mode control is a switching mode power supply （SMPS） Common control methods . Compared with voltage mode control , It has high frequency bandwidth , Thus, the dynamics of the control loop is improved , And achieve better line noise suppression . By reducing the small signal dynamics from second order to first order , It further simplifies the external voltage loop design [1]–[2].

Current mode control can be divided into average current mode and peak current mode . seeing the name of a thing one thinks of its function , Average current mode control can adjust average inductance current . Especially in boost power factor correction （PFC） In rectifier , Average current control ensures very low current distortion [8]. Peak current mode is a widely used current mode control technology , When the inductive current reaches the threshold level defined by the external voltage controller , The duty cycle terminates . This technology has some inherent advantages , For example, simple cycle by cycle current limiting and good current sharing of parallel converter [1]–[2]. The combination of average and peak current control is transition or boundary mode control , Among them, the converter is in continuous （CCM） And discontinuous conduction mode （DCM） Drive at the boundary of . The characteristic of boundary mode is the change of switching frequency , The peak current is twice the average current . however , Detecting zero current requires extra effort .

However ,CCM Peak current mode control in has several disadvantages [3]–[4]： If the duty cycle exceeds 50%, Then the control will lose stability , This leads to subharmonic oscillation , Non ideal control response caused by peak rather than average current detection and noise sensitivity , Especially when the inductance current ripple is very small .

A common way to regain stability is when the duty cycle is higher than 50%[1]–[2][3][4][5][6][7] The so-called slope compensation is applied in the peak current control converter .

With the improvement of computing power and the reduction of cost , be based on DSP And digital control of microcontroller in SMPS It becomes more and more important in applications [8]–[9][10]. This measure has many advantages , Such as flexibility and programmability , Reduce the number of active and passive components , This improves reliability , Negligible or compensable misalignment and thermal drift . Besides , Digital control also provides implementation complexity 、 The potential of adaptive and nonlinear control methods , To improve static and dynamic performance .

The full CNC converter mainly calculates the duty cycle , And use integrated digital pulse width modulation （DPWM） Generator to control the switch [9]. Besides ,[8] The full digital peak current control introduced in is based on the pre calculated duty cycle , Need to know the inductor value accurately L. Using these technologies , The inherent advantages of the above peak current control cannot be used .

However , Special for including on-chip comparator and internal input DAC Available microcontrollers including , Pure digital peak current control can basically be achieved through simple components . However , Realizing slope compensation in digital control is still challenging , Because in each switching cycle, the ramp function needs to be continuously increased .

In this paper , A digital slope compensation technology for peak current control is proposed , This technology does not use slopes , Instead, the required shutdown threshold of the comparator is calculated in advance according to the valley inductance current . Inductor value knowledge L Not required . The adaptive algorithm makes the slope compensation adjustable , To achieve the shortest response time , Without sub harmonic oscillation .

The structure of this document is as follows . The basic knowledge of peak current control with slope compensation is in Chapter II. In the third section , The digital slope compensation technology is derived , And it is verified by the simulation in the fourth section . The actual implementation and measurement results are given in Section 5 .