DK144397B - CIRCUIT FOR AUTOMATIC DISPLAY PROTECTION OF A PASSIVE POWER SOURCE - Google Patents

Description

The invention relates to a circuit for automatic discharge protection of a passive power source which is loaded by e.g. bike lights.

5 When using dynamo lights on a bicycle, the bicycle lights can only light up when the bike is running and the alternator is activated. Thus, if the bike is stationary, the lights are off, which is why the cyclist is at great risk of being overlooked in traffic. To solve this problem, it is known to use a secondary power supply in the form of a passive power source which supplies power to the lamps when the cyclist is stationary. Switching between the two power supplies 5 can take place electronically, e.g. so that the secondary power supply is switched on when the alternator voltage drops below a certain level. This is known e.g. from the specification to German Publication No. 2,443,415, which describes a circuit for charging a battery and feeding a load in the form of bicycle lights. The circuit consists of an emitter follower which, by means of a zener diode, acts as surge protector for battery and lamps. The circuit does not protect the battery, which is most advantageously made up of rechargeable Ni-Cd cells, against a powerful discharge which significantly shortens the life of the cells, decreases performance and possibly causes a repolarization.

It is admittedly known from the specification of US Patent

20 3,648,145 a circuit for disconnecting the connection between a power supply and a load when the voltage of the power supply falls below a predetermined threshold.

The electronic circuit making this switch-off consists of a transistor circuit, in which the collector-emitter-circuit a relay coil is arranged to activate a switch for switching off and on the load. The base voltage of the transistor is provided by the power supply through a voltage divider which thus charges the power supply whether the load is switched on or off. This idle 30-hour load is not quite large, but sufficient that the circuit cannot be used for a bicycle's power supply, since a bicycle is often left unused for a very long time. Thus even a modest discharge of the Ni-Cd cells could damage them.

The object of the invention is to provide a circuit for automatically discharging protection of a bicycle's secondary power supply3 which does not suffer from the above disadvantages.

This is accomplished by the power source feeding the load through the emitter-collector of a transistor, the base of this transistor through a resistor being connected to a zener diode and the common point of the resistor and the zener diode being connected to the power source through a resistor. This structure is simple and inexpensive to make and secures the power source completely against discharge when the supply voltage reaches below a threshold value determined by the zener diode. The circuit is thus particularly suitable for mounting on bicycles.

The invention is explained in more detail with reference to the drawing, which shows a circuit according to the invention coupled 15 with a generally known circuit for charging a secondary passive power source.

In the drawing a dynamo 1 is shown which is connected to two electric bulbs 20 4 and 5 via a resistor 2 and a relay switch 3, e.g. a bicycle's front and rear lights. The alternator 1 is additionally connected via a diode 6 to a set of Ni-Cd cells 7 connected in series with a fuse 8. A capacitor 9 is connected to ground parallel to the cells 7. A relay 10 is connected to the alternator 1 in series with a second diode 25 11, the relay 10 being connected in parallel with another capacitor 12. The Ni-Cd cells 7 are connected to the electric bulbs 4 and 5 through an emitter-collector circuit of the transistor 13 and the switch 3 as well as loaded by a resistor 14 and a base-connected zener diode 15. The base of the transistor 13 is connected via a resistor 16 to the zener diode 15 and thus the cells 7 through the resistor 14.

The circuit works as follows. When the alternator 1 does not produce power, the relay switch 3 is in a resting position, 35 in dotted line, whereby the electric bulbs 4 and 5 are fed, under certain conditions, as further explained, by the Ni-Cd cells 7 through the emitter of transistor 13. collector-tor circuit. When the alternator 1 starts to produce current *, the capacitor 12 is first charged through the diode 11, then a current passes through the relay 10 which 5 draws the relay switch 3 to the fully drawn line position. The electric bulbs 4 and 5 are now fed by the alternator 1, which simultaneously charges the Ni-Cd cells which are protected against excessive charging of the fuse 8. When the alternator 1 again stops producing power, 10 or produces too little current, the switches relay switch 3 returns to the dotted line position whereby Ni-Cd cells 7 take over the supply of electric bulbs 4 and 5 · If the voltage of Ni-Cd cells 7 falls to a voltage below the average voltage of the zener diode 15, go current through the zener diode 15, so that the emitter base voltage drop of the transistor 13 becomes so small that the transistor 13 turns off. Thus, switching off transistor 13 will follow the characteristics of zener diode 15. The construction shown in the example can be used within a wide range of voltage by appropriately sizing the components.

The invention has been explained above in connection with the protection of the secondary power supply of bicycle lights, but the construction can be used in connection with all power supplies.