Photosensor Circuit Current Amplifier for Relay Control
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Solution Overview
Problem
Conventional power converters used in photo controllers are inefficient, generating high heat and requiring large packages with heat sinks, and are cost-prohibitive due to the need for multiple transistors or a micro-controller, limiting their longevity and reliability, especially with the use of aluminum electrolytic capacitors that restrict the circuit's lifetime to three years.
Innovation Solution
A photosensor circuit with a pulse width modulator and voltage averaging circuit using a ceramic capacitor, a current amplifier, and a half-wave rectifier, which reduces current discharge during the negative half-cycle and allows the use of long-life ceramic capacitors, enabling efficient power conversion and extended circuit life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional power converters use large high-voltage resistors to drop voltage, then voltage conversion is achieved, but efficiency deteriorates and heat generation increases
Solution Approach 1:
The patent replaces the conventional resistor-based voltage dropping mechanism with a transistor-based switch mode power converter. The transistor acts as an electronic switch that efficiently transfers power, eliminating the need for large resistors that dissipate energy as heat. This substitution of the power conversion mechanism directly addresses both efficiency and temperature issues.
Solution Approach 2:
The patent employs pulse width modulation (PWM) technique where the transistor switches periodically between on and off states. By controlling the duty cycle of these periodic switching actions, the circuit achieves efficient voltage conversion without continuous power dissipation. The periodic switching allows energy storage in capacitors and inductors, reducing instantaneous power loss.
2Loss of energy
If switch mode power converters use multiple transistors or micro-controllers, then power conversion efficiency improves, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple functions into a single transistor-based circuit. The same transistor that performs power switching also participates in the PWM control mechanism through its collector-emitter voltage being fed back to the base. This merging of control and power functions reduces the need for separate control transistors or micro-controllers, simplifying the overall circuit while maintaining efficiency.
Solution Approach 2:
The circuit employs automatic PWM generation where the transistor's own operating conditions (collector-emitter voltage, base current) automatically regulate the switching duty cycle. The feedback from the collector to the base creates a self-regulating system that generates PWM signals without requiring external control circuits or micro-controllers, thereby reducing component count.
3Power
If aluminum electrolytic capacitors are used in the circuit, then power conversion is enabled, but reliability deteriorates due to limited lifetime
Solution Approach 1:
The patent changes the capacitor type parameter from aluminum electrolytic to ceramic capacitors. This parameter change fundamentally alters the reliability characteristics, as ceramic capacitors have significantly longer operational lifetimes and better stability. The circuit design accommodates this change by adjusting the capacitor values and positioning to maintain proper PWM operation while leveraging the superior reliability of ceramic capacitors.
4Temperature
If large packages with heat sinks are used, then heat dissipation is achieved, but device size increases
Solution Approach 1:
The patent replaces the mechanical heat dissipation system (heat sinks) with an electronic power conversion system that prevents heat generation at the source. By using transistor-based PWM switching instead of resistive voltage dropping, the circuit converts power efficiently without generating the high heat that would require heat sinks. The power semiconductor器件 itself handles thermal management through its packaging and mounting techniques.
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
The solution provides a cost-effective, efficient, and reliable power conversion system that can last up to 20 years, matching the lifespan of modern street lighting, with reduced energy consumption and improved reliability by using ceramic capacitors and a current amplifier to minimize current discharge.
Implementation Method 1
a current amplifier coupled between the voltage averaging circuit and the select transistor. The current amplifier may amplify a current discharged from the capacitor of the voltage averaging circuit to a base of the drive transistor during the negative half of the AC power source
Implementation Method 2
A half-wave rectifier coupled to the power source is configured to provide a power signal to the pulse width modulator circuit and the photo control circuit during one of the halves of the line cycle of the AC power source
Implementation Method 3
The photo control circuit includes a phototransistor that has a first terminal coupled to the power signal and a second terminal that outputs a current responsive to a level of light detected by the phototransistor
Implementation Method 4
a low pass filter circuit coupled to the second terminal of the phototransistor that filters the output current of the phototransistor to provide a light level signal voltage
Implementation Method 5
a pulse width modulator circuit configured to generate a pulse width modulated signal having a pulse width that varies responsive to an average voltage across the relay coil
Implementation Method 6
The pulse width modulator includes a voltage averaging circuit including a capacitor coupled in parallel with the relay coil
Implementation Method 7
A drive transistor is coupled between the relay coil and a neutral bus that controls the average voltage across the relay coil responsive to the pulse width modulated signal
Implementation Method 8
a relay coil configured to control application of an alternating current (AC) power source having a negative half and a positive half of a line cycle to a load
Data Source
AI summary
Photosensor circuits include a relay coil configured to control application of an alternating current (AC) power source to a load. The circuit includes a pulse width modulator circuit configured to generate a pulse width modulated signal having a pulse width that varies responsive to an average voltage across the relay coil, including a capacitor of an averaging circuit coupled in parallel with the relay coil. A drive transistor is coupled between the relay coil and a neutral bus that controls the average voltage across the relay coil responsive to the pulse width modulated signal. A photo control circuit, including a select transistor, is configured to control application of the pulse width modulated signal to the drive transistor responsive to a detected light level. The pulse width modulator circuit further includes a current amplifier coupled between the voltage averaging circuit and the select transistor. The current amplifier may amplify a current discharged from the capacitor of the voltage averaging circuit to a base of the drive transistor during the negative half of the AC power source to reduce an amount of current discharged from the capacitor of the voltage circuit .during the negative half of the AC power source.