Current Regulator

The LEDs in the lamp designed are driven using a linear current regulator. The following is a parts list for this circuit. This website will not explain how to make the circuit board as there are so many ways. This instructable outlines an excellent method of creating a board in one minute. A simple google search will lead you to an overwhelming amount of information about etching circuit boards. Any method that uses ferric chloride is usually the easiest and cheapest.

The basic operation of this circuit is quite simple. The LM334 has a tap which is a wire that measures the current running through the LEDs using a reference voltage of 64 mV. Based on the measurement it takes, the ZTX948 transistor is opened. The ZTX948 is fine for a small number of LEDs, but the maximum current that can flow through it is quite low. To combat this, the TIP32C power transistor is added in a darlington configuration. In this configuration, the ZTX948 amplifies the signal coming from the LM334 to a level that the TIP32C can use. The TIP32C is a much larger transistor that can handle a much higher current. This allows a higher number of LEDs to be used.

Parts List

Designation Item
Q1 TIP32C
Q2 ZTX948
U1 LM334
R1 100Ω 1/4 watt
R2 1kΩ 1/4 watt
C1 0.2µF Ceramic Capacitor
1.5 x 2" clad board

Heat Sink

As stated earlier, the regulator circuit actually wastes some energy as heat. Specifically, it wastes the voltage above 10.5V (what's used by the leds) through Q1. Since average battery voltage is 12V, the average ammount of power dissipated by Q1 will be (12V - 10.5V) * 0.7A, which equals to around 1W. To compensate for the small size of the transistor, we made a relatively big heatsink (the size of the entire board) from half a copper pipe, this heat sink was enough to dissipate the power from this number of leds running on the battery.

regulator board heat sink

Schematic

The circuit is very simple. This circuit does not require an etched board, it could easily be made on a piece of protoboard.

The regulator schematic.

Pictures

The picture below is showing how to connect a DC barrel plug. The terminal on the left is the ground terminal, and the terminal on the right is the positive terminal.

Current Regulatorregulator board heat sink

KiCad Files

If you are a KiCad user, you may find these files helpful. This file contains the schematics and PCB artwork used for this circuit. These files can be helpful if you are going to modify the circuit and create a new PCB layout.

KiCad Current Regulator Files