Modified Circuit for Controlled Power Supply
This circuit is a customized iteration of the design. Its primary objective is to guarantee that AC power is only directed to devices linked to K3 under specific conditions, specifically when the device connected to K2 is drawing an adequate amount of power.
Power Diodes in Series for Voltage Control
To achieve this, six power diodes are arranged in series with the load connected to K2. When the load is activated, these diodes create a voltage drop of approximately 2 V. This voltage drop is crucial, as it acts as a driving force for a triac. Subsequently, the triac becomes active and supplies power to the device connected to K3, ensuring a controlled power supply scenario.
Capacitor C1 for Circuit Stability
Capacitor C1 plays a crucial role in stabilizing the circuit by reducing its sensitivity to sudden voltage spikes.
Threshold Adjustment and Caution
To prevent premature switching caused by factors like power drawn by an AC line filter or stand-by mode, resistor R1 can be utilized to elevate the threshold level. Using a 47 Ω resistor, the threshold will be approximately 10 watts. However, this value heavily depends on the triac’s characteristics and the load current waveform. If the load current isn’t sinusoidal or if R1 is too small, the triac might trigger later, potentially failing to provide adequate power to K3, effectively turning the circuit into a dimmer.
Safety Measures during Modification
Exercise caution when altering the value of R1, considering the entire circuit operates at AC line potential. Always disconnect all components before making any adjustments.
Snubber Network for Switching Spikes
The combination of C2, R3, and R4 constitutes a snubber network, mitigating switching spikes generated by inductive loads and ensuring smoother operation.
Triac Selection and Trigger Sensitivity
An ST triac, specifically the BTA16-600SW, was chosen for its ability to handle higher current compared to the TIC225 in the original design, yet still maintain a reasonably low trigger current requirement. The ‘SW’ suffix designates it as a ‘logic level’ triac, demanding only 10 mA maximum trigger current in quadrants I and III. This feature prevents triggering imbalances in different quadrants, which could lead to equipment issues or blown fuses.
Concerns about Snubber Network Resistance
The resistance in the snubber network is comprised of two series-connected resistors (R3 and R4). It’s crucial to avoid standard resistors at AC grid voltages, as they might fail over time due to spikes, leading to triac malfunction.
Temperature Management and Load Limits
Careful attention should be given to the maximum load current. While the triac can handle around 1 A without cooling, it tends to become excessively hot. If the current exceeds 0.5 A, fitting a small heatsink is advisable. The triac’s maximum allowable junction temperature is 125 °C, but to enhance semiconductor device longevity, it’s practical to work within a 70 °C range, considering the impact of high temperatures on the device’s lifespan.
The circuit is very compact and can probably be built into the power distribution bar.