The present invention relates to H-shaped bridge circuit, and particularly to integrated circuits which include H-shaped bridge switching circuits.
H-shaped bridge circuits provide a convenient way to obtain a bipolar output from a unipolar power supply. Such circuits are very commonly used for DC motor control and other applications..sup.1 FNT .sup.1 Some examples of published literature in this area include U.S. Pat. Nos. 5,111,381, "H-bridge flyback recirculator" (filed Aug. 12, 1991); 5,111,378, "DC chopper converter"; 5,079,924, "Circuit for controlling a free-piston engine in particular of a refrigerator compressor"; 4,988,931, "Motor driving device"; and 4,562,387, "Vehicle power window control"; all of which are hereby incorporated by reference.
An example of an H-shaped bridge circuit is shown in FIG. 1. The circuit shown has an input terminal In and two output terminals Out1 and Out2 between which a load L is connected. Four bipolar transistors Q1, Q2, Q3 and Q4, of which the first two are of the pnp type and the second two are of the npn type, are connected between the output terminals Out1 and Out2 and the two poles of a direct-current voltage supply Vs in the manner shown. In the embodiment illustrated, the negative pole of the supply is connected to ground.
The bases of the transistors Q1 and Q4 are connected to two outputs of a first control circuit C1, the input of which is connected to the input terminal In. The bases of the transistors Q2 and Q3 are connected to corresponding outputs of a second control circuit C2 which is structurally identical to C1 and the input of which is connected to the terminal In by means of an inverter INV.
In operation, when a level-"1" signal is applied to the input In, the control circuit C1 makes the power transistors Q1 and Q4 conductive and the control circuit C2 keeps the power transistors Q2 and Q3 cut off. In this situation, a current IL flows through the load L in the direction indicated by the arrow in FIG. 1.
When a level-"0" signal is applied to the input In, the control circuit C1 cuts off the power transistors Q1 and Q4 and the control circuit C2 makes the transistors Q1 and Q3 conductive. A current IL thus flows through the load L in the direction opposite that indicated by the arrow of FIG. 1.
In a bridge circuit of the type described above with reference to FIG. 1, it is of fundamental importance that current should not be conducted simultaneously in the two electronic power switches which are connected to the same output terminal. Should this occur, a very large current would be drawn from the supply with a serious risk of damage to the power switches, both as a result of the high intensity of the current passing through them and because of the related thermal effects.
Some bridge circuits have circuitry for slowing the reversal of the voltage (current) in the load. In these solutions, the problem of preventing an upper power switch and the adjacent lower power switch from conducting simultaneously is more complex since the conductive power switches remain conductive throughout the time taken by the voltage in the load to change from its initial value to its final value. In order to take account of the time taken by the transition of the voltage in the load, it is therefore necessary further to delay the change to the conductive condition of the power switch which was originally cut off.
A solution commonly used to prevent the simultaneous conduction of current in the two power switches which are connected to the same output terminal in upper and lower positions consists of the introduction of a delay between the switching-off of one switch and the switching-on of the other.
Since it is difficult to determine very precisely the duration of the delay, for safety, it has to be suitably oversized.
If the bridge circuit also has means for limiting the speed of the reversal of the voltage in the load, the delay has to be increased further to take account of the voltage-transition time and the related uncertainty with which that time is determined.
In any case, long delay times limit the maximum frequency at which the current in the load can be reversed. Moreover, in bridge circuits produced in the form of integrated circuits, there is a considerable increase in the area of silicon needed.
In bridge circuits in which, after switching, the current is recirculated by the same power switch which supplied the load before switching, the other power switch must be switched on only after the time taken by the recirculation has elapsed. Since the recirculation time depends on the characteristics of the load, the provision of a given delay limits the use of the bridge circuit in question to loads of certain types.
The present invention advantageously provides an H-shaped bridge circuit of the type specified above which, in a very reliable manner, prevents the simultaneous conduction (crossover conduction) of two electronic power switches connected to the same output terminal, without having the disadvantages of the prior art outlined above.
According to one class of embodiments of the invention, this object is achieved by an H-shaped bridge circuit in which the driver circuitry includes: at least one first and one second auxiliary electronic switch which are connected respectively to an electronic power switch of the first pair and to an electronic power switch of the second pair so that, in operation, the current flowing through each auxiliary electronic switch depends on the current flowing through the associated electronic power switch, and comparator and enabling circuitry connected to the auxiliary electronic switches for supplying a signal to enable current to be conducted through one of the pairs of electronic power switches only when the current flowing through the auxiliary switch associated with the other pair has fallen below a predetermined value.
Preferably, according to a further class of embodiments, the driver circuit means include two pairs of auxiliary electronic switches, each of which is connected to an associated electronic power switch so that, in operation, the current flowing through each auxiliary switch is a fraction of the current flowing through the associated power switch. In this case, the comparator and enabling circuitry is arranged to supply the signal for enabling current to be conducted through one of the pairs of power switches only when the currents flowing through both the auxiliary switches associated with the other pair of power switches have fallen below predetermined values.
According to at least some embodiments of the present invention, there is provided an H-bridge amplifier circuit, comprising: first and second output terminals; a first pull-down power transistor connected between said first output terminal and a first power supply connection, and a first pull-up power transistor connected between said first output terminal and a second power supply connection which is more positive than said first power supply connection; and a second pull-down power transistor connected between said second output terminal and said first power supply connection, and a second pull-up power transistor connected between said second output terminal and said second power supply connection; and a first control circuit connected to control said first pull-up power transistor and said second pull-down power transistor, and a second control circuit connected to control said second pull-up power transistor and said first pull-down power transistor; said first and second control circuits each having at least one respective enable/disable input; a first auxiliary pull-down transistor connected, in parallel with said first power pull-down transistor, to provide said first control circuit with a respective monitoring current which is proportional to the current output of said first pull-down transistor; and a first auxiliary pull-up transistor connected, in parallel with said first power pull-up transistor, to provide said second control circuit with a respective monitoring current which is proportional to the current output of said first pull-down transistor; and a second auxiliary pull-up transistor connected, in parallel with said second power pull-up transistor, to provide said first control circuit with a respective monitoring current which is proportional to the current output of said first pull-down transistor; and a second auxiliary pull-down transistor connected, in parallel with said second power pull-down transistor, to provide said second control circuit with a respective monitoring current which is proportional to the current output of said first pull-down transistor; wherein said first and second control circuit each contain current-thresholding disable logic connected to receive at least two said monitoring currents from at least one of said auxiliary transistors, and to disable activation of power transistors by said control circuit if either said monitoring current is greater than a predetermined respective magnitude.
According to at least some embodiments of the present invention, there is provided an integrated circuit H-bridge amplifier, comprising: first and second output terminals; a first pull-down power transistor connected between said first output terminal and a first power supply connection, and a first pull-up power transistor connected between said first output terminal and a second power supply connection which is more positive than said first power supply connection; and a second pull-down power transistor connected between said second output terminal and said first power supply connection, and a second pull-up power transistor connected between said second output terminal and said second power supply connection; and a first control circuit connected to control said first pull-up power transistor and said second pull-down power transistor, and a second control circuit connected to control said second pull-up power transistor and said first pull-down power transistor; said first and second control circuits each having at least one respective enable/disable input; at least two different transistors selected from the group consisting of: 1) a first auxiliary pull-down transistor connected, in parallel with said first power pull-down transistor, to provide said first control circuit with a monitoring current which is proportional to and smaller than the current output of said first pull-down transistor; and 2) a first auxiliary pull-up transistor connected, in parallel with said first power pull-up transistor, to provide said second control circuit with a monitoring current which is proportional to and smaller than the current output of said first pull-down transistor; and 3) a second auxiliary pull-up transistor connected, in parallel with said second power pull-up transistor, to provide said first control circuit with a monitoring current which is proportional to and smaller than the current output of said first pull-down transistor; and 4) a second auxiliary pull-down transistor connected, in parallel with said second power pull-down transistor, to provide said second control circuit with a monitoring current which is proportional to and smaller than the current output of said first pull-down transistor; wherein said first and second control circuit each contain current-thresholding disable logic connected to receive at least one said monitoring current from at least one of said auxiliary transistors, and to disable activation of power transistors by said control circuit if said monitoring current is greater than a predetermined respective magnitude.
According to at least some embodiments of the present invention, there is provided an integrated circuit H-bridge amplifier, comprising: first and second output terminals; a first pull-down power device connected between said first output terminal and a first power supply connection, and a first pull-up power device connected between said first output terminal and a second power supply connection which is more positive than said first power supply connection; and a second pull-down power device connected between said second output terminal and said first power supply connection, and a second pull-up power device connected between said second output terminal and said second power supply connection; and a first control circuit connected to control said first pull-up power device and said second pull-down power device, and a second control circuit connected to control said second pull-up power device and said first pull-down power device; said first and second control circuits each having at least one respective enable/disable input; at least two different devices selected from the group consisting of: 1) a first auxiliary pull-down device connected to said first power supply connection and connected to be controlled by said second control circuit in parallel with said first power pull-down device and connected to supply an enable signal to said first control circuit accordingly; and 2) a first auxiliary pull-up device connected to said second power supply connection and connected to be controlled by said first control circuit in parallel with said first power pull-up device and connected to supply an enable signal to said second control circuit accordingly; and 3) a second auxiliary pull-up device connected to said second power supply connection and connected to be controlled by said second control circuit in parallel with said second power pull-up device and connected to supply an enable signal to said first control circuit accordingly; and 4) a second auxiliary pull-down device connected to said first power supply connection and connected to be controlled by said first control circuit in parallel with said second power pull-down device and connected to supply an enable signal to said second control circuit accordingly.
According to at least some embodiments of the present invention, there is provided an integrated circuit H-bridge amplifier, comprising: first and second output terminals; a first pull-down power transistor connected between said first output terminal and a first power supply connection, and a first pull-up power transistor connected between said first output terminal and a second power supply connection which is more positive than said first power supply connection; and a second pull-down power transistor connected between said second output terminal and said first power supply connection, and a second pull-up power transistor connected between said second output terminal and said second power supply connection; and a first control circuit connected to control said first pull-up power transistor and said second pull-down power transistor, and a second control circuit connected to control said second pull-up power transistor and said first pull-down power transistor; said first and second control circuits each having at least one respective enable/disable input; at least two different transistors selected from the group consisting of: 1) a first auxiliary pull-down transistor connected to said first power supply connection and connected to be controlled by said second control circuit in parallel with said first power pull-down transistor and connected to supply an enable signal to said first control circuit accordingly; and 2) a first auxiliary pull-up transistor connected to said second power supply connection and connected to be controlled by said first control circuit in parallel with said first power pull-up transistor and connected to supply an enable signal to said second control circuit accordingly; and 3) a second auxiliary pull-up transistor connected to said second power supply connection and connected to be controlled by said second control circuit in parallel with said second power pull-up transistor and connected to supply an enable signal to said first control circuit accordingly; and 4) a second auxiliary pull-down transistor connected to said first power supply connection and connected to be controlled by said first control circuit in parallel with said second power pull-down transistor and connected to supply an enable signal to said second control circuit accordingly.
According to at least some embodiments of the present invention, there is provided a method for operating an H-bridge switching circuit in accordance with a digital input signal, comprising the steps of: when said digital input signal is in a first state: turning on a first pull-down power transistor, which is connected to drive said first output terminal low, and turning off a first pull-up power transistor which is connected to drive said first output terminal high when turned on, and turning on a second pull-up power transistor which is connected to drive said second output terminal high, and turning off a second pull-down power transistor which is connected to drive said first output terminal low when turned on; when said digital input signal is in a second state opposite to said first state: turning off said first pull-down transistor, and turning on said first pull-up power transistor, and turning off said second pull-up transistor, and turning on said second pull-down transistor; monitoring the current passed by said first pull-up power device, and blocking said step (a.i.) whenever the instantaneous value of the current passed by said first pull-up power device is greater than a predetermined quantity; and monitoring the current passed by said second pull-up power device, and preventing said step (b.iv.) whenever the instantaneous value of the current passed by said second pull-up power device is greater than a predetermined quantity.
According to at least some embodiments of the present invention, there is provided a method for operating an H-bridge switching circuit in accordance with a digital input signal, comprising the steps of: when said digital input signal is in a first state: turning on a first pull-down power transistor, which is connected to drive said first output terminal low, and turning off a first pull-up power transistor which is connected to drive said first output terminal high when turned on, and turning on a second pull-up power transistor which is connected to drive said second output terminal high, and turning off a second pull-down power transistor which is connected to drive said first output terminal low when turned on; when said digital input signal is in a second state opposite to said first state: turning off said first pull-down transistor, and turning on said first pull-up power transistor, and turning off said second pull-up transistor, and turning on said second pull-down transistor; monitoring the current passed by said first pull-up power device, and blocking said step (a.i.) whenever the instantaneous value of the current passed by said first pull-up power device is greater than a predetermined quantity; and monitoring the current passed by said second pull-up power device, and preventing said step (b.iv) whenever the instantaneous value of the current passed by said second pull-up power device is greater than a predetermined quantity; monitoring the current passed by said first pull-down power device, and preventing said step (b.ii.) of turning on said first pull-up power transistor whenever the instantaneous value of the current passed by said first pull-down power device is greater than a predetermined quantity; and monitoring the current passed by said second pull-down power device, and preventing said step (a.iii.) of turning on said second pull-up power transistor whenever the instantaneous value of the current passed by said second pull-down power device is greater than a predetermined quantity.
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