CIRCUIT FOR AUTOMATIC DISCHARGE PROTECTION OF A PASSIVE CURRENT SOURCE

Abstract: In a circuit for the discharge protection of a passive current source (7) a load (4, 5) is fed via the emitter collector circuit of a transistor (13), the basis of said transistor (13) being connected to a zener diode (15) via a resistor (16), the joint point of the resistor (16) and the zener diode (15) being connected to the current source (7) via a resistor (14). Thus a simple and effective cutting out of the load (4, 5) is achieved, when the voltage of the current source (7) falls below a threshold value determined by the zener diode (15).

Description: CIRCUIT FOR AUTOMATIC DISCHARGE PROTECTION OF A PASSIVE CURRENT SOURCE. The invention relates to a circuit for automatic discharge protection of a passive current source, which is loaded by e.g. bicycle lamps. When using dynamo lamps on a bicycle, the bicycle lamps can only emit light during bicycling, i.e. when the dynamo lamp is activated. When the bicycle is at a standstill, the lamps are off which means that the cyclist is running a great risk of being overlooked in the traffic. In order to solve this problem it is known to use a secondary current source in the form of a passive current source furnishing the lamps with current when the cyclist is stopping. The change-over be ¬ tween these two power sources may take place electronically for instance so that the secondary power source is cut in when the voltage of the dynamo falls below a certain level. This is known from e.g. the specification to DT-OS No. 2, 3,41 describing a circuit for charging a battery and feeding a load in the form of bicycle lamps. The circuit co sists of an emitter follower which by means of a zener diod functions as excess-voltage protection for battery and lamp The circuit does not protect the battery which most advanta geously is constituted by rechargeable Ni-Cd-cells, against a considerable discharging, shortening the lifetime of the cells considerably, reducing the efficiency and perhaps cau a change in polarizing. From the specification to US Patent No . 3 , 648 , 145 a circuit is already known which causes a break in the connection be¬ tween a power circuit and a load when the voltage of the cu rent source falls below a predetermined threshold value . Th electronic circuit performing this cutting out consists of transistor circuit in the collector emitter circuit of whic a relay coil is adapted to operate a switch for cutting out and cutting in the load . The base voltage of the transistor is provided by the current source via a voltage divider whi thus loads the current source whether the load is cut in or cut out . This idle load is not very heavy, however , but eno as to make the device unfit for delivering the power supply to a bicycle, as a bicycle often remains unused for a very long period . Even a moderate discharging of the Ni-Cd-cells may thus cause damage to them. It is the object of the present invention to provide a circuit for auto matic discharge protection of a secondary current source of a bicycle, which is not encumbered with the abovementioned disadvantages. This is achieved in that the current source feeds the load via the emitter col lector circuit of a transistor, that the basis of this transistor is connected to a zener diode via a resistor, and that the joint point of ( X/y-r, - W °'' Λ -' * resistor and the zener diode is connected to the current source via a resistor. This construction is simple and inexpensive to produce and secures the current source completely against discharging when the supply voltage falls below the threshold value determined by the zener diode. The circuit is thus especially suitable for being mounted on bicycles . In the following the invention will be further described with reference to the drawing which shows a circuit according to the invention, " which is coupled with a generally known circuit for charging a secondary pas- sive current source. On the drawing a dynamo 1 is shown, which is connected to two electrical bulbs 4 and 5, e.g. the front and rear lights of a bicycle, via a resis¬ tor 2 and a relay switch _>. The dynamo 1 is furthermore via a diode 6 connected to a number of Ni-Cd-cells 7 , which are connected in series to a circuit breaker 3. A capacitor 9 is earthed parallel to the cells 7 - A relay 10 is connected to the dynamo 1 in series with another diode 11, the relay 10 being connected in parallel to another capacitor 12. The Ni- Cd-cells 7 are connected to the electrical bulbs 4 and 5 via the emitter collector circuit of a transistor 13 and the switch 3, and loaded by a resistor 14 and a zener diode 15 connected in series. The basis of the transistor 13 is via a resistor 16 connected to the zener diode 15 and thus to the cells 7 via the resistor 14. The circuit is functioning in the following manner . When the dynamc 1 does not produce power , the re lay swit c h 3 is in a position of rest , shown with a dot -and-dash line , so that the electrical bulbs 4 and 5 under certain conditions , which will be explained later , are fed by the Ni-Cd-cells 7 via the emitter collector circuit of the transistor 13 - When the dynamo 1 starts to produce power , the capacitor 12 is first charged through the diode 11 , whereupon power starts to run through the relay 10 , which draws the relay switch 3 to the position shown with the solid line . The electrical bulbs 4 and 5 are now fed by the dynamo 1 , whic h simultaneously charges the Ni-Cd-cells , which are protected against a too powerfull charging by the circuit breaker 8. When the dynamo 1 again stops producing power, or produces too litt power, the relay switch 3 switches back to the position shown with the dot-and-dash line, whereby the Ni-Cd-cells take over the feeding of the electrical bulbs 4 and 5. If the voltage of the Ni-Cd-cells 7 falls to a voltage below the puncture voltage of the zener diode 1 , power cannot pass through the zener diode 15 _ which means that the emit basis voltage drop of the transistor 13 is switched off. Thus the switch-off of the transistor 13 will follow the characteristic of the zener diode 15. The construction sho in the example can be used within a large voltage range by suitably dimensioning the components. The invention is not limited to the use shown in the examp i.e. protection of the secondary current source of bicycle lamps, as the construction may be used in connection with all kinds of current sources.

Claims: C A I M Circuit for automatic discharge protection of a current source which is loaded by e.g. * bicycle lamps, c h a r a c t e r i z e d i n that the current source (7) feeds the load (4, 5) via the emitter collector circuit of a tran-- sistor (13), that the basis of this transistor (13) via a resistor (lβ) is .connected to a zener diode (15), and that the joint point of the resistor (16) and the zener diode (15) is connected to the current source via a resis¬ tor (14).

Inventors: DUNCH P
Applicants: DUNCH P
Application year: 1980
Main classification: B62J5
IPC codes: B62J6, H02H3, H02H7, H02J7