private void cargaCombo()
        {
            cnx = new SqlConnection(cdn);
            cmd = new SqlCommand();
            cmd.Connection = cnx;
            ch = new Conceptos.Core.ConceptosHelper();
            ch.Command = cmd;

            Conceptos.Core.Conceptos concepto = new Conceptos.Core.Conceptos();
            concepto.idempresa = GLOBALES.IDEMPRESA;

            if (rbtnDeducciones.Checked)
                concepto.tipoconcepto = "D";
            if (rbtnPercepcion.Checked)
                concepto.tipoconcepto = "P";

            List<Conceptos.Core.Conceptos> lstConceptos = new List<Conceptos.Core.Conceptos>();

            try
            {
                cnx.Open();
                lstConceptos = ch.obtenerConceptosDeducciones(concepto, _periodo);
                cnx.Close();
                cnx.Dispose();
            }
            catch (Exception error)
            {
                MessageBox.Show("Error: \r\n \r\n" + error.Message, "Error");
            }

            cmbConcepto.DataSource = lstConceptos;
            cmbConcepto.DisplayMember = "concepto";
            cmbConcepto.ValueMember = "id";
        }