Let be a time scale, that is, is a nonempty closed subset of . Let be fixed and be points in , an interval denoting time scales interval, that is, Other types of intervals are defined similarly. Some definitions concerning time scales can be found in [1–5].
In this paper, we are concerned with the existence of positive solutions for the following nonlinear first-order periodic boundary value problem on time scales:
where is a positive parameter, , is right-dense continuous, , and for each and represent the right and left limits of at .
The theory of impulsive differential equations is emerging as an important area of investigation, since it is a lot richer than the corresponding theory of differential equations without impulse effects. Moreover, such equations may exhibit several real world phenomena in physics, biology, engineering, and so forth, (see [6–8]). At the same time, the boundary value problems for impulsive differential equations and impulsive difference equations have received much attention [9–19]. On the other hand, recently, the theory of dynamic equations on time scales has become a new important branch (see, e.g., [1–5]). Naturally, some authors have focused their attention on the boundary value problems of impulsive dynamic equations on time scales [20–27]. In particular, for the first-order impulsive dynamic equations on time scales
where is a time scale which has at least finitely-many right-dense points, is regressive and right-dense continuous, is given function, . The paper  obtained the existence of one solution to problem (1.2) by using the nonlinear alternative of Leray-Schauder type.
In , Benchohra et al. considered the following impulsive boundary value problem on time scales
They proved the existence of one solution to the problem (1.3) by applying Schaefer's fixed point theorem and the nonlinear alternative of Leray-Schauder type.
In , Li and Shen studied the problem (1.3). Some existence results to problem (1.3) are established by using a fixed point theorem, which is due to Krasnoselskii and Zabreiko, and the Leggett-Williams fixed point theorem.
In , the first author studied the problem (1.1) when . The existence of positive solutions to the problem (1.1) was obtained by means of the well-known Guo-Krasnoselskii fixed point theorem.
Recently, Sun and Li  considered the following periodic boundary value problem:
By using the fixed point index, some existence, multiplicity and nonexistence criteria of positive solutions to the problem (1.4) were obtained for suitable .
Motivated by the results mentioned above, in this paper, we shall show that the problem (1.1) has at least three positive solutions for suitable by using the Leggett-Williams fixed point theorem . We note that for the case and problem (1.1) reduces to the problem studied by .
In the remainder of this section, we state the following theorem, which are crucial to our proof.
Let be a real Banach space and be a cone. A function is called a nonnegative continuous concave functional if is continuous and
for all and .
Let be constants,
Theorem 1.1 (see ).
Let be a completely continuous map and be a nonnegative continuous concave functional on such that Suppose there exist with such that
Then has at least three fixed points in satisfying