A novel single-stage single-switch (S4) LED driver is proposed in this paper. The paper focuses on the operation principles of the
power stage circuit with an operation switched between Critical Conduction Mode (CRM) and Discontinuous Conduction Mode
(DCM), including steady state analysis, simulation and backed up by experimental results. The results verify that this proposed
LED driver can obtain a high power factor (PF) and the dc output is relatively stable.