4volts to 14volts zenor diodes

[MrAl]

Hello again,

From your drawing it looks as if you can use a circuit with a PNP transistor instead of an NPN. The PNP emitter would be connected to V+ and the collector to the top of the LEDs. The base would connect through the current limiting resistor and to the cathode of the zener. The zener anode would connect to ground.
Do you want to try this circuit instead?

 

[MikeMl]

Ok, then without a very complex switch-mode voltage boost converter, the best you can do is to put a 4.5V Zener in-series with your LEDs. This means that the LEDS will only get 12-4.5V = 7.5V when the lamp driver puts out 12V, and the LEDs will not light at all when the lamp driver puts out 4V.