T3SE type 3 SE

Description: The all-transistor T3SE operates similarly to a conventional switch mode power supply (SE). Like the Tritium model, it activates when the charging current falls below a specified threshold. After the circuit is triggered, positive feedback is utilized to latch the circuit, which resets at a predetermined voltage on the main capacitor. When the capacitor discharges, the solar cell begins to charge the main capacitor primarily through the base-emitter junction of transistor Q1 and some current passing through a 1K resistor, which has a maximum forward voltage drop of 0.6V. This condition causes the collector of Q1 to become saturated, bringing the collector voltage close to the emitter voltage of Q1. Consequently, this clamps the base-emitter junction of Q2, cutting off the collector current of Q2 that would normally flow into the base of Q3. When the voltage across the 1K resistor falls below 0.6V (i.e., 1 KOhm x 0.6 mA), Q1 exits saturation and "unclamps" the base of Q2. This allows Q2 to turn on, with base current supplied through a 220K resistor. Once Q2 is activated, it provides base current to Q3, thereby energizing the load, which in this case is a motor. The base-emitter voltage drop across Q3 establishes the reset voltage and prevents the solar cell from charging capacitor C1 during the discharge phase, which would otherwise deactivate the T3SE. When Q3 is activated, its collector supplies current to the motor and additional base current to Q2 through a 100K resistor. This dual positive feedback mechanism enables the T3SE to switch on quickly with minimal voltage drop across Q3. Omitting the 1K resistor (i.e., setting its value to infinity) alters the behavior of the T3SE. As long as the solar cell generates a voltage higher than that of the capacitor, the SE will not activate. A simple gesture in front of the solar cell can trigger it. In fact, without the 1K resistor, the T3SE functions effectively as a D1-type switch mode power supply.

The T3SE circuit employs a combination of transistors for efficient operation, utilizing Q1, Q2, and Q3 to create a feedback loop that enhances performance. The solar cell serves as a primary energy source, charging the main capacitor until it reaches a threshold voltage. The role of Q1 is crucial as it initially senses the condition of the circuit. When the current through the 1K resistor drops below the threshold, Q1 transitions from saturation to an active state, allowing Q2 to turn on.

Q2’s activation is pivotal because it provides the necessary base current to Q3, which drives the load. The 220K resistor connected to Q2 ensures that it receives adequate base current to turn on fully. The interaction between Q2 and Q3 is characterized by a positive feedback mechanism, where Q3 not only powers the motor but also reinforces the base current to Q2 through the 100K resistor. This configuration leads to rapid switching, minimizing energy loss and enhancing efficiency.

The reset mechanism is dictated by the voltage drop across Q3, which, when reached, prevents the solar cell from continuing to charge the capacitor during the load's discharge phase. This ensures that the T3SE remains in an active state until the load is no longer needed.

In scenarios where the 1K resistor is omitted, the circuit behavior changes significantly. The solar cell must always maintain a higher voltage than the capacitor for the T3SE to remain inactive. This feature allows the circuit to be sensitive to environmental changes, such as light variations, making it suitable for applications where responsive switching is desired. Overall, the T3SE design showcases a sophisticated use of transistor technology to achieve efficient switching and energy management.The all-transistor T3SE works much like a conventional SE: like the Tritium, it fires when the charging current drops below the minimum and after the circuit triggers, positive feedback is used to latch the circuit, resetting at a fixed voltage on the main cap. When the cap is discharged, the solar cell starts to charge the main cap mostly throug h the base - emitter junction of Q1 and some current passing through the 1K resistor with a maximum forward voltage drop of. 6V. This causes the collector of Q1 to be saturated and the voltage on the collector will be close to the Q1 emitter voltage.

This clamps the base emitter junction of Q2 and cuts off the Q2 collector current which would otherwise flow into the base of Q3. When the voltage across the 1K resistor drops below. 6V (i. e. , 1 KOhms x 0. 6 mA), Q1 comes out of saturation and "unclamps" the Q2 base. This allows Q2 to turn on with base current supplied through the 220 K resistor. When Q2 turns on, it supplies base current to Q3 and the load (here a motor) is picked up. The Q3 base emitter voltage drop sets the reset voltage and also stops the solar cell from charging C1 during the discharge which would otherwise cause the T3SE to turn off again.

When Q3 turns on, the Q3 collector supplies motor current but also additional Q2 base current through the 100K resistor. The double positive feedback makes the T3SE switch on rapidly with little wasted voltage drop on Q3. Leaving the 1K resistor out (i. e. , setting its value to infinity) changes the T3SE behaviour. As long as the solar cell is generating a higher voltage than the capacitor voltage, the SE won`t fire.

Wave your hand in front of the solar cell and it fires. In fact, without the 1K resistor, the T3SE makes an excellent D1-type SE.