The invention is based on a level converter according to the type of the independent claim.
Out DE 101 20 672 A1
For example, a level converter is known in which a level is changed from a first DC voltage level to a second DC voltage level.
level converter according to the invention
with the characteristics of the independent
In contrast, claims
the advantage that this level converter has only one transistor
that is wired in such a way that the logical input level
is transferred to the output without inversion. This will be a
Threshold voltage is used as the switching threshold that causes
from your logical input level to the corresponding logical one
Output level is switched. This is a very inexpensive and
a level converter. The level converter should preferably be between
a transmitter and a receiver
Act. An advantageous circuit measure is the use of the pull-down resistor in order to
blocking the transistor's output level to that of the pull-down resistor
to pull the applied voltage. Under supply voltage is here
understand any voltage provided to adjust the voltage
Output level serves. This includes
also voltages derived from the supply voltage, for example via voltage dividers
to be provided.
Input voltage, for example 0 / 3.3 V, is at a first outer electrode
connected, for example the emitter. 0 V means for example
Low and 3.3 V high. The output voltage can then be tapped at the collector.
The logic output level is determined, for example, by the voltage across the pull-up resistor
set, for example 5 V, preferably the supply voltage
This voltage of 5 V or the supply voltage has a value
which the output voltage should reach at its maximum level.
At an input level of 0 V, the output level will also be
have a value of 0 V. The 5 V output level could be high
correspond and the output level of 0 V Low. Other level conversions
by virtue of
The level converter according to the invention is also special in terms of its simple construction
space-saving. The outer electrode
designate collector and emitter or source and drain,
the center electrode denotes the base or the gate.
those in the dependent
Measures listed claims
and further developments are advantageous improvements of the independent claim
specified level converter possible.
It is advantageous that the transistor either as a bipolar transistor
or as an n-channel field effect transistor
can be trained. The base / drain voltage divider becomes
Setting the threshold voltage, i.e. a switching threshold, is used.
It is possible,
to do without the voltage divider if a suitable voltage
available in the affected system
is. Furthermore, the resistance of the voltage divider,
which is connected to ground, a capacitor in parallel on the
and ensures fast switching edges of the output signal. So that is
enables a faithful reproduction of the input signal.
is the level converter between a processor or microcontroller
and a communication bus such as the CAN bus in a control unit for restraint systems
connected. It is possible,
that the level converter between circuits with different
logical levels is used.
it is provided that the supply voltage of the receiver is not
is used to adjust the threshold voltage, but only
to adjust the output level. The threshold voltage will then
set by the supply voltage of the transmitter. The supply voltage
can then only be used, for example, to adjust the output level
be used. This circuit measure enables easy follow-up
of fluctuations in the respective supply voltages due to the
Output level. Fluctuations in the supply voltage of the transmitter
affect the switching behavior of the transistor and fluctuations
the supply voltage of the receiver
act directly on the output level.
the invention are shown in the drawing and are in the
following description in more detail
Show it 1 a block diagram, 2 a first circuit diagram of the level converter according to the invention and 3 a second circuit diagram of the level converter.
1 shows in a block diagram the use of the level converter according to the invention. A microcontroller μC in a control unit for restraint systems is connected to the level converter LS via a data output. The level converter LS is connected to a CAN bus CAN via a data output. The microcontroller uses a maximum voltage level for its signals of 3.3 V. However, the CAN bus uses a voltage level of 5 V. Consequently, a level converter is required to convert the signals of the microcontroller from 3.3 V to 5 V.
2 now shows the inventive design of the level converter. An input voltage is at an emitter of a transistor T1 20 connected, which has a low level and a high level. The low level is at 0 V, while the high level is at 3.3 V. On the one hand, a resistor R3 is connected to the collector of transistor T1 and, on the other hand, an output for an output voltage 21 , The output voltage 21 , which is intended here for the CAN bus, should also have a low level of 0 V, but a high level of 5 V. The resistor R3 is on its other side with a resistor R1 and a supply voltage VDD on an electrode 22 connected. The supply voltage VDD has a level of 5 V, ie exactly the level that the output voltage 21 should be at high level. The resistor R1 is connected on its other side to a base as the center electrode of the transistor T1 and to a parallel circuit comprising a resistor R2 and a capacitor C 1. The parallel connection of the capacitor C 1 and the resistor R2 is connected to ground on its other side.
Is now on a connection 20 the input voltage at the low level, i.e. 0 V, then the collector-emitter path of the transistor T1 is conductive, since the voltage VDD of 5 V across the voltage dividers R1 and R2 causes a voltage drop on the base-emitter path such that the transistor T1 is conductive. The voltage divider R1 and R2 must therefore take this into account. The result is that even at the exit 21 there is a low level of 0 V, since the transistor T1 is conductive and no significant voltage drops and on the other side at the connection 20 0 V are also present. Now go to the connection 20 the voltage from 0 V to the high level of 3.3 V, then this voltage change affects the resistors R3, R1 and R2 on the base-emitter voltage, which was previously at a level of 0 V at the input 20 was determined solely by the voltage VDD of 5 V. The one at the connector 20 Rising voltage thus reduces the base-emitter voltage, so that the transistor T1 is moved into the blocked region. This results in the switching behavior of the level converter. The dimensions of the resistors R3, R1 and R2 are such that the blocking of the collector-emitter path of the transistor T1 at 3.3 V is at least fulfilled. This voltage therefore serves as a threshold voltage. However, if transistor T1 is blocked, the full 5 V are present at resistor R3, since the current can no longer flow through transistor T1, but only through the output 21 , This 5 V accordingly causes the high level of 5 V.
Capacitor C1 provides
clean and fast switching edges of the S-V output signal to ensure a true to the original
To allow playback of the input signal. The resistor R3
so here the function of a so-called "pull-up resistor". It is possible here
to use other voltage values.
then the resistors
R1, R2 and R3 and the capacitor C1 can be dimensioned. As
the transistor T1 can
Bipolar transistors or n-channel field effect transistors are used
Dimensioning example is possible:
R1 = 34.8 kΩ,
R2 = 21.5 kΩ,
R3 = 3.48 kΩ, C1
= 22nF and T1 = BC846B.
3 shows a further embodiment of the invention. The same designations are used here for the same components. The only difference to 2 is that the resistor R3 is now connected on the first side to the supply voltage VDD2 of the receiver and on the other side to the collector of T1 and the output 21 , In addition, R1 is connected to VDD1 on its first side. VDD1 denotes the transmitter supply voltage. On its second side, R1 is like in 2 connected to the base of T1 and the parallel connection of R2 and C1. Consequently, two supply voltages VDD1 and VDD2 are used for the circuit here. The threshold voltage for the transistor T1 is set via the supply voltage VDD1 of the transmitter and the output voltage via the supply voltage VDD2 of the receiver. The level converter according to the invention can thus also be used for slightly dynamic supply voltages, because either the dynamics of VDD 1 act on the threshold voltage and thus the switching behavior of the transistor and / or VDD2 acts directly on the output voltage of the level converter due to their dynamics. The high levels of the level converter correspond to the supply voltages of the transmitter and receiver.