Please tell me how to write this formula.

=IF(E4="H",0,IF(F4="Y",275,(RATE*O4)))

The above statement works fine but it gives me the worng answer. The maximum
amount cannot exceed 275 and the minimum cannot be less than 150. The
portion of the formula beginning at F4 really needs to say:

IF F4=Y,(RATE*O4),BUT NOT LESS THAN 150 OR MORE THAN 275

In english, the cell occupied by this formula should equal the sum of
(RATE*O4) but the result cannot be less than 150 or more than 275.

Can anyone helP?