You sound confused by the amounts that are being used in the preparation of your tax return.
You do not get a personal exemption for a dependent any more. The new tax law eliminated that. The amount of $4150 comes into play to determine whether someone who is not your qualified child can be claimed as a dependent. If the "qualified relative" you want to claim as a dependent has income over $4150, they cannot be claimed as a dependent.
The $12,000 is the standard deduction for someone who filing Single or Married Filing Separately. The standard deduction lowers the amount of income you are taxed on. It is not a refund.
https://ttlc.intuit.com/questions/4482394-how-will-tax-reform-affect-my-2018-federal-tax-return
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