Datasheet HVLED007 (STMicroelectronics) - 10

Application information HVLED007 Equation 1
T I    ON in = 1- Ip ------ 2 pk  T 
Figure 4. Hi-PF QR flyback converter with the traditional TM control: current waveforms
Tș TON With the traditional TM control method, the term Ippk (θ), the peak envelope of the primary current, is sinusoidal (Ippk(θ) = Ippk sin θ). The distortion stems from the term TON / T(θ), due to the primary current being chopped, which is not constant (TON is constant, T(θ) is not). This distortion is prevented if the flyback converter is operated with a fixed switching frequency in the Discontinuous Conduction Mode (DCM). However, there are a few benefits in using TM operation that are lost when operating with a fixed frequency (FF): lower conducted EMI emissions, safer operation under short-circuit conditions, valley-switching or even true soft-switching (zero-voltage switching, ZVS). The idea behind the novel TM method is to distort the current reference Vcsref(θ) that determines Ippk(θ) (Ippk(θ) = Vcsref (θ) / Rs) by a term T(θ) / TON : this cancels out the term TON / T(θ) introduced by averaging and results in a sinusoidal average primary current, i.e. in a sinusoidal input current. Then, the control objective can be expressed in the following terms:
Equation 2
  Vcs   ref  = Vcsx sin  T  ---------- T  ON 10/33 DS12866 Rev 1 Document Outline Table 1. Device summary 1 Block diagram Figure 1. Block diagram Table 2. Absolute maximum ratings 2 Pin connections Figure 2. Pin connection (top view) Table 3. Thermal data Table 4. Pin functions (continued) 3 Electrical characteristics Table 5. Electrical characteristics (continued) 4 Application information 4.1 Introduction Figure 3. Input current distortion in Hi-PF QR flyback converters with traditional TM control: current shape and resulting total harmonic distortion and power factor vs. Kv (= Vinpk/VR) ratio 4.2 Input current shaping function - operating principle Figure 4. Hi-PF QR flyback converter with the traditional TM control: current waveforms Figure 5. Input current shaper (ICS) block and its interconnection with HVLED007 control Figure 6. Key waveforms of the ICS circuit in figure 5 Figure 7. Shape of the current reference Vcsref(θ) (5) at different input voltages (i.e. Kv values) 4.3 Operation of a Hi-PF QR flyback converter based on the HVLED007 Table 6. Timing quantities in a HVLED007-based Hi-PF QR flyback converter Table 7. Control quantities in a HVLED007-based Hi-PF QR flyback converter Table 8. Electrical quantities in a HVLED007-based Hi-PF QR flyback converter 4.4 Shaping capacitor (Ct) selection (pin CT) 4.5 Control input for isolated feedback and optocoupler driving (pin COMP) Figure 8. Output characteristic of pin COMP and significant levels 4.6 Multiplier input for input voltage sensing (pin MULT) 4.7 Current sensing input (pin CS). Sense resistor (Rs) selection Figure 9. Effect of ripple on Ct on current sense signal: a) within linear dynamics, close to clamp level; b) signal slightly exceeding clamp level; c) signal exceeding clamp level, with OCP activation 4.8 Zero current detection and triggering block (pin ZCD); starter 4.9 Overload and short-circuit protection (OCP function) Figure 10. Functional schematic of the overload and short-circuit protection function 4.10 Overvoltage protection (OVP function) Figure 11. Functional schematic of the OVP function 4.11 Soft-restart function Figure 12. Functional schematic of the soft restart function 4.12 Suggested step-by-step design procedure of a Hi-PF QR flyback converter based on the HVLED0007 Table 9. Basic electrical specification and key parameters of a Hi-PF QR flyback Figure 13. Typical application schematic (reference for suggested design procedure) 5 Referenced documents 6 Package information Table 10. SO-8 mechanical data Figure 14. Package dimensions 7 Revision history Table 11. Document history