**Exhibit 31.2**

**CERTIFICATIONOF PRINCIPAL FINANCIAL OFFICER PURSUANT TOEXCHANGE ACT RULE 13a-14(a) and 15d-14(a)AS ADOPTED PURSUANT TO SECTION 302OF THE SARBANES-OXLEY ACT OF 2002**

I,Paul E. Ross, Vice President—Finance, Treasurer and Chief Financial Officer ofPower-One, Inc., certify that:

1.                Ihave reviewed this Annual Report on Form 10-K of Power-One, Inc.;

2.                Basedon my knowledge, this report does not contain any untrue statement of amaterial fact or omit to state a material fact necessary to make the statementsmade, in light of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report;

3.                Basedon my knowledge, the financial statements, and other financial informationincluded in this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report;

4.                Theregistrant’s other certifying officer and I are responsible for establishingand maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) and internal control over financial reporting (as defined inExchange Act Rules 13a-15(f) and 15d-15(f)) for theregistrant and have:

(a)           Designedsuch disclosure controls and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure that materialinformation relating to the registrant, including its consolidatedsubsidiaries, is made known to us by others within those entities, particularlyduring the period in which this report is being prepared;

(b)          Designedsuch internal control over financial reporting, or caused such internal controlover financial reporting to be designed under our supervision, to providereasonable assurance regarding the reliability of financial reporting and thepreparation of financial statements for external purposes in accordance withgenerally accepted accounting principles;

(c)           Evaluatedthe effectiveness of the registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period covered by thisreport based on such evaluation; and

(d)          Disclosedin this report any change in the registrant’s internal control over financialreporting that occurred during the registrant’s most recent fourth fiscalquarter that has materially affected, or is reasonably likely to materiallyaffect, the registrant’s internal control over financial reporting; and

5.                Theregistrant’s other certifying officer and I have disclosed, based on our mostrecent evaluation of internal control over financial reporting, to theregistrant’s auditors and the audit committee of the registrant’s board ofdirectors (or persons performing the equivalent function):

(a)           Allsignificant deficiencies and material weaknesses in the design or operation ofinternal control over financial reporting which are reasonably likely toadversely affect the registrant’s ability to record, process, summarize andreport financial information; and

(b)          Any fraud, whether ornot material, that involves management or other employees who have asignificant role in the registrant’s internal control over financial reporting.

| Date: March 9, 2006                      |
|-----------------------------------------------|
| /s/ PAUL E. ROSS                              |   |
| Paul E. Ross                                  |
| *Vice  President—Finance, Treasurer and* |
| *Chief  Financial Officer*                    |
| *(Principal  Financial Officer)*              |

 

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