2V4稳压管 2V5-N0.5 2V5-N0.5-EI 2V5-N0.5-EI-W 2V5-N0.5-W 2V5-P0.5 2V5-P0.5-EI 2V5-P0.5-EI-W 2V5-P0.5-W 2V5P4