Triac Heater Power Control Using Zero-Cross Capacitor Gating
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Solution Overview
Problem
Existing power control circuits using a triac for image forming apparatuses face challenges in continuously supplying gate current due to capacity constraints of separate power sources, leading to triac turn-off issues from AC voltage distortion and noise, necessitating costly and complex solutions to maintain triac conduction.
Innovation Solution
A power control device with a zero-cross detecting unit, triac, supplying unit, and controlling unit that controls triac states using control signals across multiple AC voltage half-waves, discharging and charging electric charge based on zero-cross points to manage triac conduction and non-conduction states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate power source is used to supply gate current to the triac, then the triac can be controlled to turn on, but the capacity of the separate power source limits the duration of gate current supply
Solution Approach 1:
The patent combines the separate power source with the AC power source by using the AC power source itself to charge the capacitor that supplies gate current. This merging eliminates the capacity limitation of a separate small power source while maintaining the ability to control the triac reliably.
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the AC power source and the triac gate. The capacitor charges from the AC power source during low-demand periods and discharges to provide gate current when needed, mediating the energy transfer and solving the duration limitation.
2Duration of action of stationary object
If electric charges are continuously supplied to the power source for the gate current, then the triac can be substantially continuously turned on, but this requires a power source with large electric charge capacity or continuous charging circuitry
Solution Approach 1:
The system uses itself to charge the capacitor - the AC power source that already exists in the circuit is used to charge the capacitor during periods when the triac is not needing gate current. This self-service approach eliminates the need for external charging circuitry and large capacity power sources.
Solution Approach 2:
The capacitor charging occurs periodically during the AC cycle when the triac is not requiring gate current. This periodic charging action allows continuous triac operation without requiring continuous external power supply or complex charging circuitry.
3Reliability
If the triac is continuously controlled to avoid AC power source distortion and noise influence, then stable power control is achieved, but this requires sophisticated control mechanisms that increase cost
Solution Approach 1:
The capacitor is charged in advance during periods when the AC power source is stable and noise-free. This preliminary charging action stores clean energy that can be used to supply gate current during periods when the AC power source might be distorted or noisy, avoiding the need for complex real-time control mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively manages triac conduction without separate power source capacity constraints, reducing costs and noise interference, ensuring stable power supply to heaters in image forming apparatuses.
Implementation Method 1
a capacitor connected in parallel with the heater; a controlling unit configured to control a state of the triac... the supplying unit discharges an electric charge when the control signal is outputted in the half-wave of each of the first polarity and the second polarity and charges the electric charge when the control signal is not outputted
Implementation Method 2
a heater configured to generate heat by being supplied with an AC voltage; a triac configured to switch a conduction state in which the AC voltage is supplied to the heater
Data Source
AI summary
A power control device includes a heater, a zero-cross detecting unit, a triac, a supplying unit, and a controlling unit. The supplying unit discharges an electric charge when a control signal is outputted in a half-wave of each of a first polarity and a second polarity and charges the electric charge when the control signal is not outputted in the half-wave of the first polarity. The controlling unit outputs: in a first half-wave, a first control signal on the basis of the zero-cross point and a second control signal in a first phase different in timing from the first control signal, and in a second half-wave, a third control signal on the basis of the zero-cross point and a fourth control signal in a second phase different in timing from the second control signal. The first phase and the second phase are different from each other.