battery is fed by short impulses of high intensity current by means of discharges from two capacitors which are alternately charged and discharged by transistor switches opened and closed by externally supplied impulses the battery current is thus kept substantially constant and low a series of digits or segments thereof if used may be fed in sequence with the impulses application_number US 57697675 A description if a capacitor is charged through a resistance from a source of current and then discharged through an led the current from the feed source of the device would be in the form of impulses and it is preferable that this current is constant to fulfill this condition as shown in fig3 two capacitors are used which are charged and discharged alternately in fig3 two capacitors 1 and 2 are respectively charged via current paths i1 and i2 connected to a feed source or battery v bb and the capacitors 1 and 2 the positive terminals of the capacitors are connected to the emitters of two transistors 3 and 4 the collectors of which are connected in common to the anode of an led 5 the cathode of which is grounded the bases of the transistors 3 and 4 are supplied with impulse trains a and b fig4 the two trains are complementary so that at each period of the signal a or b a discharge of the respective capacitor 1 or 2 takes place.