Imagine a safety net for your lights, a backup light circuit is like a trusty teammate for your lamps.
It usually has two or more lights and a clever system.
If one light burns out, the circuit automatically turns on another one making sure you never get left in the dark.
This is especially helpful for important areas like hallways or safety lights.
Circuit Working:
Parts List:
| Component Type | Description | Quantity |
|---|---|---|
| Resistors | 100k 1W | 1 |
| 47k | 1 | |
| 22k | 1 | |
| Capacitors | Ceramic 47nF 50V | 2 |
| Semiconductors | Triac BT136 | 2 |
| Diac | 2 | |
| LED Lamps | 2 | |
| Other | Fuse 1A | 1 |
This table organizes the components by type and lists the quantity for each component specified.
This backup light circuit ensures that if lamp 1 burns out lamp 2 will illuminate.
However, it is essential to replace lamp 1, otherwise the circuit will not function if lamp 2 burns out.
Lamp 1 is in series with the Tri2 triac.
R3 and C2 create a delay network.
Once the voltage across C2 exceeds 30V, diac D2 conducts triggering Tri2 and lighting lamp 1.
The control circuit for Lamp 2 is parallel to lamp 1s, but R2 C1 has double the timing of R3 C2 preventing Tri1 from triggering when Tri2 conducts.
If Lamp 1 burns out voltage is present across both RC networks through Lamp 2 and R1 causing Tri2 to trigger first.
However, because its current is lower than the holding current Tri2 stops conducting almost immediately.
In this scenario, C1 continues to charge, and Tri1 will eventually trigger.
Due to the slightly longer time constant for lamp 2 compared to lamp 1 the intensity of lamp 2 will be slightly lower.
If you desire equal light intensity for both lamps choose lamp 1 with a higher nominal power.
The triacs can handle powers up to 100 W each without heatsinks and up to 1000 W with heatsinks.
It is not recommended to use light bulbs with a power less than 25W as they may flicker.
Absolute Maximum Rating System of Triac BT136
| Symbol | Parameter | Conditions | Min | Max | Unit |
|---|---|---|---|---|---|
| VDRM | repetitive peak off-state voltage | – | 600 | V | |
| IT(RMS) | RMS on-state current | full sine wave; Tmb≤107℃ | – | 4 | A |
| ITSM | non-repetitive peak on-state current | full sine wave; Tj(init)=25℃; tp=20 ms | – | 25 | A |
| full sine wave; Tj(init)=25℃; tp=16.7 ms | – | 27 | A | ||
| I²t | I2t for fusing | tp=10 ms SIN | – | 3.1 | A²s |
| dIT/dt | rate of rise of on-state current | IT = 6 A; IG = 0.2 A; dIG/dt = 0.2 A/µs T2+ G+ | – | 50 | A/μs |
| IT = 6 A; IG = 0.2 A; dIG/dt = 0.2 A/µs T2+ G- | – | 50 | A/μs | ||
| IT = 6 A; IG = 0.2 A; dIG/dt = 0.2 A/µs T2- G- | – | 50 | A/μs | ||
| IT = 6 A; IG = 0.2 A; dIG/dt = 0.2 A/µs T2- G+ | – | 10 | A/μs | ||
| IGM | peak gate current | – | 2 | A | |
| PGM | peak gate power | – | 5 | W | |
| PG(AV) | average gate power | over any 20 ms period | – | 0.5 | W |
| Tstg | storage temperature | -40 | 150 | ℃ | |
| Tj | junction temperature | – | 125 | ℃ |
How to Build:
To build a Simple Backup Light Circuit mentioned below are the connections steps:
Connect Lamp 1 and Tri2 in series:
- Connect one terminal of Lamp 1 to one terminal of Triac Tri2.
- Connect the other terminal of Lamp 1 to the power source.
- Connect the other terminal of Triac Tri2 to the other terminal of the power source.
Add resistors and capacitors:
- Connect resistor R1 in series with Lamp 1 and Triac Tri2.
- Connect capacitor C2 in parallel with R3.
- Connect capacitor C1 in parallel with resistor R2
Connect Diac to Triac Tri2:
- Connect one terminal of Diac D2 to the junction of R3 and C2.
- Connect the other terminal of Diac D2 to the gate terminal of Triac Tri2.
Note:
- This circuit provides a backup lighting system that switches to an alternate lamp if one fails ensuring continuous illumination.
Conclusion:
The backup light circuit described ensures continuous lighting by automatically switching to a backup lamp if the primary lamp fails.
It employs a series of components such as triacs, diacs, resistors and capacitors to detect and respond to lamp failures providing a reliable backup lighting solution.