A switched current error amplifier (SC-EA) was proposed for the use of buck converters. In the buck structure, the system could be kept stable without off-chip compensation, saving chip area and obtaining higher power density. The bandwidth of the error amplifier adaptively changed with the switching frequency, and it still had good stability and fast transient response speed at high frequency. The on-chip frequency compensation was realized by using the valley current mode COT structure of the switching current mode error amplifier, and the off-chip components were omitted. The multi-channel parallel current sharing was realized, and the transient response speed was faster. The circuit was designed in a 018 μm BCD process. The simulation results showed that the loop stability and adaptive bandwidth could be achieved by selecting 10 μF and 70 μF output capacitors at 6 MHz and 1 MHz switching frequency, respectively. At the switching frequency of 6 MHz, the upper and lower step transient response time was 63 μs and 55 μs, respectively. At the switching frequency of 1 MHz, the upper and lower step transient response time was 277 μs and 284 μs, respectively.