Triac - Q4025P - Alternistor, 400V, 25A, Fastpack TO-3 Base Alternistors are specifically designed for applications which are required to switch highly inductive loads To accomplish this, a special chip is has been designed which effectively offers the same performance as two thyristors (SCRs) wired inverse parallel (back to back); hence the alternistor has better turn-off behavior than a standard triac.