Current steering module for use with LED strings
In an embodiment, a lamp control circuit is provided. The lamp control circuit includes an intermediate current steering block configured to be coupled to a cathode of a first light-emitting device of a plurality of light-emitting devices and a final current steering block configured to be coupled to a cathode of a final light-emitting device of the plurality of light-emitting devices. The final current steering block is configured to disable the intermediate current steering block and conduct current when a voltage input to the plurality of light-emitting devices is sufficient to activate all of the plurality of light-emitting devices.
1. A lamp control circuit, comprising:
an intermediate current steering block configured to be coupled to a cathode of a first light-emitting device of a plurality of light-emitting devices;
a final current steering block configured to be coupled to a cathode of a final light-emitting device of the plurality of light-emitting devices, wherein the final current steering block is configured to disable the intermediate current steering block and conduct current when a voltage input to the plurality of light-emitting devices is sufficient to activate all of the plurality of light-emitting devices; and
a current source coupled to the intermediate current steering block, and further coupled to the final current steering block.
2. The lamp control circuit of claim 1 , wherein at least one of the plurality of light-emitting devices is a light emitting diode (LED).
3. The lamp control circuit of claim 1 , wherein at least one of the plurality of light-emitting devices is an organic light emitting diode (OLED).
4. The lamp control circuit of claim 1 , wherein the intermediate current steering block comprises:
a first NFET coupled drain-to-source between a cathode of a first one of the plurality of light-emitting devices, and a first intermediate node; and
a second NFET coupled drain-to-source between the first intermediate node and the current source.
5. The lamp control circuit of claim 1 , wherein the final current steering block comprises:
a third NFET coupled drain-to-source between a cathode of a second one of the plurality of light-emitting devices, and a second intermediate node; and
a fourth NFET coupled drain-to-source between the second intermediate node and the current source.
6. The lamp control circuit of claim 5 , wherein the third NFET has a gate electrode coupled to a positive voltage source; and the fourth NFET has a gate electrode coupled to the positive voltage source.
7. The lamp control circuit of claim 6 , wherein the first NFET has a gate electrode coupled to the positive voltage source; and the second NFET has a gate electrode coupled to an output terminal of a first inverting amplifier.
8. The lamp control circuit of claim 7 , wherein the first inverting amplifier has an input terminal coupled to second intermediate node.
9. The lamp control circuit of claim 8 , further comprising:
a second inverting amplifier;
wherein the second inverting amplifier has an input terminal coupled to the first intermediate node.
10. The lamp control circuit of claim 9 , further comprising:
a holding path block coupled between the output of a full-wave rectifier and the current source.