The most common sources of power for electric lamps are :-
(a) Low Voltage AC mains supply ( 100 to 230 volts ) at 50 Hz
(b) Extra Low Voltage AC supply ( < 100 volts ) from a magnetic transformer at 50Hz
(c) Extra Low Voltage AC supply from a Switch Mode Power Supply
(d) Extra Low Voltage DC supply from a Switch Mode Power Supply
(e) Extra Low Voltage DC (eff) supply from a Switch Mode Power Supply
(f) Smooth Extra Low Voltage DC from a battery
A Switch Mode Power Supply with an output rated at 12 v DC (eff) will produce an output that if supplied to an incandescent lamp would have the same heating effect as a smooth 12 volt DC supply from ( for example ) a battery.
The output voltage from a Switched Mode Power Supply rated as 12 v DC (eff) fluctuates at high frequency but averages out to be 12 volts DC. This may be 24 volts on for half the time and then off for half the time . or 36 volts on for 1/3 of the time and then off for 2/3 of the time. This type of voltage regulation is known as Pulse Width Modulation ( PWM )
Incandescent lighting
Incandescent lamps are a metal filament in a glass or quartz envelope filled with an inert gas that allows the filament to become white hot without burning and thus emit white light.
The filament is heated by passing an electric current through it. The amount of current is determined by the voltage applied to the ends of the filament and the electrical resistance of the filament.
An incandescent lamp is self contained and needs no external device to control the current through it. Provided the voltage applied to the ends of the filament is equal to or less than the lamps rated voltage then the lamp will not be damaged. It can be a DC voltage, an AC voltage or a DC (eff) voltage. A DC (eff) supply with large fluctations in output voltage at high frequency may cause the filament to vibrate ( electro-magnetic effect ) and thus reduce the mechanical life span of the lamp.
LED Lighting
LED lamps use Light Emitting Diodes to produce light. The LED itself is a semiconductor diode that produces light when a current flows through it. It has no effective internal resistance and therefore cannot control the current that passes through it when a voltage is applied.
A semiconductor diode also has a threshold voltage. If the voltage applied to the diode is less than the threshhold ( typically 3 volts for a "white" LED ) then the diode will not pass any current and not produce any light. When the applied voltage is greater than the threshold the diode becomes zero resistance and will pass as much current as the power source can provide. Without some form of current control the diode will be destroyed+
An LED lamp consists of one or more LEDs and a means to control the current that passes through them
The means to control the current can be :->
(1) a simple resistor for lamps that operate from a stable DC supply
(2) an electronic LED driver that produces a controlled DC current appropriate for the LED(s) in the lamp.
Electronic LED drivers use Switch Mode Current Control to regulate the current supplied to the LED(s)
The electronic LED driver built into the lamp has to be compatible with the type of power source that is supplying the lamp if it to properly control the current it supplies to the LED element(s).
The current control circuit of all LED drivers requires a DC power source. LED drivers intended for use on AC supplies will include a rectifier to produce DC power and a capacitor to provide some smoothing of the DC power supplied to the current control circuit.
Dimming and Pulsing LED elements
An LED element can be dimmed by reducing the DC current driven through it.
An LED element can be made to appear brighter to the human eye by driving pulses of high current through it. The pulses can be several time the rated current provide the gap between them give an average current less than the rated continuous current. An LED element pulsing at 50 pulses per second or faster will appear in the human eye to be continuous lit.
Pulsing can produce a bright light with much reduced power consumption for warning beacons. It should not be used for work lights as a strobing effect on moving items will occur.
Compatibility Issues
The voltage on the terminals of the LED element will be about 3 volts . This is determined by the LED element and not by the amount of current driven through the LED element by the LED driver. A driver can drive current through several elements connected in series, the number of series connected element is determined by the maximum voltage the driver can produce on it's terminals while still regulating the current.
The three most common type of LED lamp are
(a) Battery operated lamp which has just a driver and element(s)
(b) ELV lamp which has rectifier and driver and element(s)
(c) Mains lamp which has voltage reduction and rectifier and driver and elements
Some ELV operated lamps will not accept a ELV DC supply.
When an ELV lamp is supplied with ELV AC 50 Hz reduced from mains voltage by a magnetic transformer there are few if any compatibility problems. Some ELV Operated lamps will not operate on a DC supply
Items labelled as "electronic transformers" are Switch Mode Power Supplies
An electronic transformer does not produce an ELV AC supply at 50 Hz hence when the ELV supply is from an electronic transformer compatibilty cannot be assured and the risk of unstable operation of the driver is high.
The majority of electronic transformers produce a fluctuating DC voltage that averages out to the rated voltage. The fluctuations can include voltage spikes large enough to damage the electronics in the driver. The fluctuations can disturb the operation of the driver resulting in unstable control of the current driven through the LED element.
An item labelled as an LED driver should not be used to supply power to any type of lamp other than one or more LED elements connected in series.
An LED driver is designed to drive ( force ) it's rated current through what ever is connected across it's output terminals. The voltage on the LED driver's output will be set such that the rated current is flowing out of the driver and through the item connected to it. If the item being supplied normally takes less than the LED driver's rated current then the LED driver will increase the voltage on it's output until the rated curren is flowing. This high voltage and excessive current will damage the LED driver inside the lamp.
(a) Low Voltage AC mains supply ( 100 to 230 volts ) at 50 Hz
(b) Extra Low Voltage AC supply ( < 100 volts ) from a magnetic transformer at 50Hz
(c) Extra Low Voltage AC supply from a Switch Mode Power Supply
(d) Extra Low Voltage DC supply from a Switch Mode Power Supply
(e) Extra Low Voltage DC (eff) supply from a Switch Mode Power Supply
(f) Smooth Extra Low Voltage DC from a battery
A Switch Mode Power Supply with an output rated at 12 v DC (eff) will produce an output that if supplied to an incandescent lamp would have the same heating effect as a smooth 12 volt DC supply from ( for example ) a battery.
The output voltage from a Switched Mode Power Supply rated as 12 v DC (eff) fluctuates at high frequency but averages out to be 12 volts DC. This may be 24 volts on for half the time and then off for half the time . or 36 volts on for 1/3 of the time and then off for 2/3 of the time. This type of voltage regulation is known as Pulse Width Modulation ( PWM )
Incandescent lighting
Incandescent lamps are a metal filament in a glass or quartz envelope filled with an inert gas that allows the filament to become white hot without burning and thus emit white light.
The filament is heated by passing an electric current through it. The amount of current is determined by the voltage applied to the ends of the filament and the electrical resistance of the filament.
An incandescent lamp is self contained and needs no external device to control the current through it. Provided the voltage applied to the ends of the filament is equal to or less than the lamps rated voltage then the lamp will not be damaged. It can be a DC voltage, an AC voltage or a DC (eff) voltage. A DC (eff) supply with large fluctations in output voltage at high frequency may cause the filament to vibrate ( electro-magnetic effect ) and thus reduce the mechanical life span of the lamp.
LED Lighting
LED lamps use Light Emitting Diodes to produce light. The LED itself is a semiconductor diode that produces light when a current flows through it. It has no effective internal resistance and therefore cannot control the current that passes through it when a voltage is applied.
A semiconductor diode also has a threshold voltage. If the voltage applied to the diode is less than the threshhold ( typically 3 volts for a "white" LED ) then the diode will not pass any current and not produce any light. When the applied voltage is greater than the threshold the diode becomes zero resistance and will pass as much current as the power source can provide. Without some form of current control the diode will be destroyed+
An LED lamp consists of one or more LEDs and a means to control the current that passes through them
The means to control the current can be :->
(1) a simple resistor for lamps that operate from a stable DC supply
(2) an electronic LED driver that produces a controlled DC current appropriate for the LED(s) in the lamp.
Electronic LED drivers use Switch Mode Current Control to regulate the current supplied to the LED(s)
The electronic LED driver built into the lamp has to be compatible with the type of power source that is supplying the lamp if it to properly control the current it supplies to the LED element(s).
The current control circuit of all LED drivers requires a DC power source. LED drivers intended for use on AC supplies will include a rectifier to produce DC power and a capacitor to provide some smoothing of the DC power supplied to the current control circuit.
Dimming and Pulsing LED elements
An LED element can be dimmed by reducing the DC current driven through it.
An LED element can be made to appear brighter to the human eye by driving pulses of high current through it. The pulses can be several time the rated current provide the gap between them give an average current less than the rated continuous current. An LED element pulsing at 50 pulses per second or faster will appear in the human eye to be continuous lit.
Pulsing can produce a bright light with much reduced power consumption for warning beacons. It should not be used for work lights as a strobing effect on moving items will occur.
Compatibility Issues
The voltage on the terminals of the LED element will be about 3 volts . This is determined by the LED element and not by the amount of current driven through the LED element by the LED driver. A driver can drive current through several elements connected in series, the number of series connected element is determined by the maximum voltage the driver can produce on it's terminals while still regulating the current.
The three most common type of LED lamp are
(a) Battery operated lamp which has just a driver and element(s)
(b) ELV lamp which has rectifier and driver and element(s)
(c) Mains lamp which has voltage reduction and rectifier and driver and elements
Some ELV operated lamps will not accept a ELV DC supply.
When an ELV lamp is supplied with ELV AC 50 Hz reduced from mains voltage by a magnetic transformer there are few if any compatibility problems. Some ELV Operated lamps will not operate on a DC supply
Items labelled as "electronic transformers" are Switch Mode Power Supplies
An electronic transformer does not produce an ELV AC supply at 50 Hz hence when the ELV supply is from an electronic transformer compatibilty cannot be assured and the risk of unstable operation of the driver is high.
The majority of electronic transformers produce a fluctuating DC voltage that averages out to the rated voltage. The fluctuations can include voltage spikes large enough to damage the electronics in the driver. The fluctuations can disturb the operation of the driver resulting in unstable control of the current driven through the LED element.
An item labelled as an LED driver should not be used to supply power to any type of lamp other than one or more LED elements connected in series.
An LED driver is designed to drive ( force ) it's rated current through what ever is connected across it's output terminals. The voltage on the LED driver's output will be set such that the rated current is flowing out of the driver and through the item connected to it. If the item being supplied normally takes less than the LED driver's rated current then the LED driver will increase the voltage on it's output until the rated curren is flowing. This high voltage and excessive current will damage the LED driver inside the lamp.