The solution is to add a push-pull output. The following arrangement has been chosen as it swings almost rail-to-rail but two faults need to be addressed.
Both transistors turn on during the brief interval when pin 3 is travelling from high to low or low to high.
This means the two transistors will put a "short" across the power rail.
The addition of the 4R4 will allow a high current to flow but the transistors will not be damaged. In addition, green LEDs on the base of each transistor reduces the time when both transistors are ON.
The animation shows how the transistors are turned on and off and deliver a high current to the load. The animation shows how NPN and PNP transistors follow an input signal in a push -pull arrangement using positive and negative supply rails. This is not the same as our circuit however the basic effect applies. The output is inverse of pin3 but pin3 only needs to deliver 10-50 milliamp and the transistors can deliver 1 amp or more to the load. This allows the 555 to be kept cool.
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