Low voltage dimmer with no load protection
First Claim
1. A low voltage dimmer circuit for delivering power to a load through a low voltage transformer having a primary side and a secondary side, said low voltage light dimmer circuit connecting between an AC power line and said load, said low voltage dimmer circuit comprising:
- triac connected between said AC power line and said load to permit current flow therethrough during any half cycle of AC power upon receiving a gate signal;
charging means connected across said triac to charge to a predetermined voltage within a given period of time after zero crossing of said AC power if said load is connected across said secondary side of said low voltage transformer, said charge to said predetermined voltage taking longer than said given period of time if no said load is connected across said secondary side of said low voltage transformer;
computer means receiving said AC power to determine the time of said zero crossing and expiration of said given period of time, said computer means supplying said gate signal to said triac;
during operation of said low voltage light dimmer circuit said gate signal being sent for selected said half cycle to trigger said triac into conduction if said predetermined voltage is reached within said given period of time.
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Accused Products
Abstract
A low voltage dimmer is shown with the dimming function being on a primary side of a low voltage transformer. Live voltage feeds through a triac to the primary side of the transformer with the gate for the triac being controlled by a microprocessor. To prevent burnout of the transformer if the secondary load side is open, zero crossing of the incoming signal is determined by the microprocessor. If the time constant between the zero crossing of the live voltage and the charging of a capacitor with resistance being provided by the primary side of the transformer exceeds w predetermined time period, the microprocessor will be inhibited from generating a pulse to fire the triac. When the primary side of the transformer has been opened, the load on the secondary side can be re-established, i.e. light bulb replaced. Power for the microprocessor is from the charging of a capacitor used to provide the triggering signal to the microprocessor. Also the microprocessor may be triggered from remote locations.
75 Citations
13 Claims
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1. A low voltage dimmer circuit for delivering power to a load through a low voltage transformer having a primary side and a secondary side, said low voltage light dimmer circuit connecting between an AC power line and said load, said low voltage dimmer circuit comprising:
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triac connected between said AC power line and said load to permit current flow therethrough during any half cycle of AC power upon receiving a gate signal; charging means connected across said triac to charge to a predetermined voltage within a given period of time after zero crossing of said AC power if said load is connected across said secondary side of said low voltage transformer, said charge to said predetermined voltage taking longer than said given period of time if no said load is connected across said secondary side of said low voltage transformer; computer means receiving said AC power to determine the time of said zero crossing and expiration of said given period of time, said computer means supplying said gate signal to said triac; during operation of said low voltage light dimmer circuit said gate signal being sent for selected said half cycle to trigger said triac into conduction if said predetermined voltage is reached within said given period of time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of controlling power delivered from an AC power line through a low voltage circuit to a load via a low voltage transformer having a primary side and a secondary side, said method including the following steps:
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connecting a triac between said AC power and said load to permit current flow therethrough during any half cycle of AC power upon receiving a gate signal; charging a charge storing device connected across said triac to a predetermined voltage after zero crossing of said AC power, said predetermined voltage being reached in less than a predetermined time only if said load is connected to said secondary side of said low voltage transformer; using a computer to measure time from said zero crossing to said charging of said predetermined voltage so that if said predetermined voltage is reached in said predetermined time said computer will supply said gate signal to said triac. - View Dependent Claims (10, 11, 12, 13)
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Specification