excel - Prevent custom error bars from going into negative values -

i have bar charts custom value error bars. adjusted values sothat add 1/2 of value negative , 1/2 positive direction (basically make error bar half run through actual bar of graph , other half stick out above).

however, few of error bar values high cross x-axis , go negative. ideally, adjust exact error bars (and, if possible, no other bars in row of data). i'd have them moved upwards sothat don't cross x-axis, instead stick out above actual bar little more.

does know way of doing this?

say have values in column , errors (half values) in column b. use function in c:

=if(b1-a1>0,a1,b1) 

and in d:

=if(b1-a1>0,2*b1-a1,b1) 

then use values c negative errors , values d positive errors.