Circuit arrangement for the controlled supply to a load

A circuit for supplying a constant DC voltage to an electrical load and, alternatively, a relatively constant DC current to a storage battery connected in parallel with the electrical load, the circuit including a blocking oscillator having a transformer with primary and secondary windings, a switching transistor having first and second load terminals and a control terminal, and a first resistor, the primary winding, the load terminals of the switching transistor and the first resistor being connected in series across an input voltage source, a rectifier connected in series with the electrical load across the secondary winding, a controlling transistor having first and second load terminals and a control terminal, a reference voltage element connected across the load terminals of the controlling transistor and connected to the control terminal of the switching transistor, and a Zener diode having an anode connected to the control terminal of the controlling transistor and a cathode connected to the parallel arrangement of the electrical load and the storage battery.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a circuit for converting varying line voltages 
over a wide range and for selectively supplying either a constant voltage 
to power a DC motor or a constant current to charge a storage battery. 
With portable electric and electronic devices, it is desirable that they 
can be operated at various voltages, or, if they have storage batteries, 
that these storage batteries can be charged at various voltages. For 
example, electric shavers, electronic flash units, portable radios, or the 
like are often taken along on journeys abroad and are then operated in the 
various countries with different line voltages. These line voltages 
generally vary on the one hand between 110 volts and 240 volts and on the 
other hand between 50 Hz and 60 Hz. 
To adapt the small units, and specifically storage batteries, to the 
various voltages, one needs to transform the voltage, which can be done 
capacitively or inductively. 
2. Description of the Prior Art 
A transistor converter circuit is already known, which can generate on the 
one hand a charging current for a storage battery and on the other hand a 
higher direct current for driving a motor (DE-OS No. 20 14 377, U.S. Pat. 
No. 3,568,038). This device has a high-frequency through-flow transformer 
with a saturable core, whose primary side is connected to the rectified 
line voltage and whose secondary side supplies the desired current. The 
known circuit can be operated only at a particular line voltage, and 
therefore does not automatically adapt itself to different voltages. Since 
the core of the transformer always reaches the saturation region, its 
efficiency is low, and there are thermal problems. 
Furthermore, a circuit arrangement is known for the controlled supply to a 
load from input voltage sources of various voltages. This arrangement uses 
a blocking oscillator type converter, whose primary coil is in series with 
a switching transistor and an emitter resistor (U.S. Pat. No. 4,005,351). 
A secondary coil here feeds the load, and feedback is effected through 
another coil. Another transistor is connected to the base of the switching 
transistor. The voltage drop at the emitter resistor is applied through a 
diode to the base of the second transistor. The switch-on time of the 
switching transistor here depends strongly on the input voltage, i.e. the 
oscillation frequency of the blocking oscillator type converter depends 
very strongly on the input voltage and becomes higher with increasing 
input voltage. To compensate this undesirable circumstance, a relatively 
expensive control circuit has been provided. 
Another known circuit arrangement accounts for the influence of the input 
voltages on the primary side directly, that is not through the detour via 
another control circuit and a time delay. This is done by adding another 
current component to the primary current that is flowing over the emitter 
resistor. Said current component corresponds to the input voltage, for 
example, is directy proportional to it (No. P 29 49 421.1-32). As the 
input voltage rises, the primary current is then shut off earlier, i.e. at 
a lower value, in such a fashion that the output power has a predetermined 
dependency on the input voltage, and in particular is dependent on it. A 
disadvantage of this circuit arrangement is that stabilization of the 
charge current is not very good. 
Finally, another circuit arrangement is known, which uses the voltage drop 
across the emitter resistor, in order to cut off when a particular primary 
current is reached (DE-OS No. 27 51 578). In addition, a control voltage 
is derived from another coil during the blocking phase of a converter. 
Said control voltage also influences the cut-off time, so that a certain 
characteristic curve is achieved. As the input voltage increases, the 
feedback becomes stronger, which counteracts the cut-off through the 
primary current. The subsequent control circuit therefore must 
additionally also compensate the larger feedback current. 
SUMMARY OF THE INVENTION 
In general, the invention features a blocking oscillator converter circuit 
selectable between a first mode for supplying a relatively constant volage 
to an electrical load, e.g., a motor, and a second mode for generating a 
relatively stable charging current.

The input voltage U.sub.N is here conducted through a rectifier 3 to a 
capacitor 4, one of whose terminals is grounded. The collector-emitter 
line of a switching transistor 7 is connected in series with the primary 
coil 5. Here the emitter of the transistor 7 is grounded through a 
resistor 8. A diode 9 and a zener diode 10 are situated in parallel to the 
primary coil 5, and their cathodes are connected. The anode of diode 9 is 
connected both to the primary coil of the transformer 6 and to a resistor 
11. Through a capacitor 12 and a resistor 13, the resistor 11 is connected 
with a secondary coil 14 of the transformer 6. A zener diode 15 is also 
connected with the capacitor 12 and the resistor 11. The zener diode 15 is 
connected in parallel to the base-emitter line of the transistor 7. Here 
the emitter of this transistor 7 is grounded not only through the resistor 
8 but also through a capacitor 16. From the cathode of the zener diode 15 
and respectively from the base of the transistor 7, a connection leads to 
the conductor of a transistor 17, whose base is connected with two 
resistors 18, 19. Of these two transistors, the resistor 19 is grounded 
and the other resistor is connected with the collector of the transistor 
17. The base of the transistor 17 is also connected to the anode of a 
zener didoe 20, whose cathode is connected with a terminal of the motor 1. 
A switch 21 is situated between this terminal and the storage battery 2. 
The other terminal of the motor 1 is connected through a choke 22 with the 
storage battery 2 and a resistor 23. Here, this resistor 23 is grounded 
and is connected with the anode of a diode 24, whose cathode is connected 
to a terminal of the secondary coil 14 of the transformer 6. A capacitor 
25 is situated between the other terminal of said secondary coil 14 of the 
transformer 6 and the anode of the diode 24. Another capacitor is 
connected between the ground and the terminal of the motor 1 and 
respectively the choke 22. That end of the choke 22 which is connected to 
the storage battery 2 can be grounded through a switch 26. 
As regards the mode of operation of the circuit arrangement according to 
the drawing, one must distinguish between the operating state in which the 
switches 21, 26 are closed and the operating state in which the switches 
21, 26 are open. In the closed state, the motor 1 is driven while, in the 
opened state, the storage battery 2 is charged. The circuit arrangement 
with the switches open will be considered first. If an alternating line 
voltage U.sub.N is applied to the rectifier 3, it will be rectified by the 
latter and will be applied to the capacitor 4. Then the capacitor 12 will 
be charged through the resistor 11, until the transistor 7 becomes 
conducting. Since the primary coil represents an inductance, the current 
through the transistor 7 rises linearly. This current causes a 
corresponding voltage drop at the resistor 8. When the voltage at the 
resistor 8 has risen to such an extent that the sum of the voltage at the 
resistor 8 and of the base-emitter voltage of resistor 7, which is 
required for current to flow, reaches the breakdown voltage of the zener 
diode 15, the current through the transistor 7 can rise no further. Thus 
the magnetic field in the transformer 6 collapses. The voltage of the 
secondary coil 14 of the transformer 6 changes in polarity, and the diode 
24 becomes conducting, so that the capacitor 25 charges up. Furthermore, 
the base voltage of the transistor 7 becomes more and more negative with 
respect to ground. The battery 2, which is connected in parallel to the 
capacitor 25, as well as the motor 1, receive a voltage which is formed at 
the capacitor 25. When this voltage exceeds the cut-off voltage of the 
zener diode, the transistor 17 becomes conducting and connects the base of 
the transistor 7 to ground. Thus, the b.o. type converter stops operating. 
Only when the voltage at the battery 2, as a consequence of current 
consumption to the motor 1, has been reduced to such an extent that the 
zener diode 20 and thus the transistor 7 again become blocking can the 
b.o. type converter again oscillate. 
During operation with closed switches 21, 26, the circuit shown in the 
drawing forms a constant voltage source. 
The zener diode 10 and the diode 9 essentially have the purpose of removing 
the peaks of kick-back voltage pulses, which form because of stray 
inductance. 
The light-emitting diode 30 can indicate whether the battery 2 is being 
charged. If the battery 2 is not being charged, the switches 31, 21, 26 
are all closed, i.e. the diode 30 is short-circuited and does not light up 
.