Dual Universal Hardware Driver for Embedded Systems

Petre Tzv. Petrov Sofia, Bulgaria

1983

Cautions

We may use 7407 instead on 7406 but in that case the active levels of the control signals will be inverted.

Both circuits are with open collectors at the outputs.

With appropriate Darlington transistors we may obtain output current to more than 10A, but it is strongly recommended to limit the output current up to around 3-5A.

It is recommended to use Fuse F1 for maximum 3A.

Also we should make appropriate conductors on the pcb in order to meet large currents.

The filtering capacitors C1 to C6 should not be omitted.

C1 should be at least 470uF per Ampere.

C2 to C5 are from 0.15 to 0.47uF/63V.

We may connect loads to ANY combination of the output connectors CON1 to CON5 under the condition that the transistors are not overloaded and the algorithm of the controlling these loads is appropriate.

Jumpers J1 and J2 are giving the possibility to control the driver with just two signals.

It is not recommended to use these jumpers at high frequencies and high loads.

In most of the cases for the optimal and safe control we should use all four signals and the jumpers should be open, e.g. in many cases we are need to obtain “dead time” for the control pulses.

During that “dead time” all transistors are OFF!

Again transistors T1 and T2 and transistors T3 and T4 should never be ON in the same time!
Resistors R5 to R8 are obligatory.

They are in the range from 0.1Ohm to 0.47Ohm and with power dissipation at least 2W.

The power supply

The connector CON6 is for the power supply and the control signals in the same time.

The driver has two power supplies Vcc and +Vee.

Vcc is the standard power supply for 7406 or 7407 or Vcc = 5V+-5%.

+Vee is the peripheral power supply.

It can be anywhere between 6V and 30V, preferably above 10V.

It should be noted that the maximal power supply for the open collector of 7406/7407 is 30V.

Vee is protected with fuse F1.

The fuse F1 should be fast and for appropriate current ratings.

The driver can work with 12V and 24V rechargeable batteries.

Heat sinks

Transistors T1, T2, T3 and T4 should be obligatory mounted on appropriate heat sinks according to the targeted applications.

T1 and T2 can be mounted on common heat sink without insulations because usually the metallic part of the package is connected with the collectors.

T3 and T4 also can be mounted on common heat sink.

If we use two separate heat sinks for T1+T2 and T3+T4 they should be with thermal resistance below 15C/W.

If we use common heat sink for all four transistors it should be with thermal resistance below 10C/W.

The size of the heat sinks depends on the loads and the power supply.

In practice we should keep attention at least for the following:

1/ The frequency of the switching should be appropriate.
If the frequency is too high the transistors can overheat.
2/ When possible the temperature of the transistors should be monitored.
3/ When possible we should have additional over current protection in the power supply.
4/ At high currents and high switching frequencies we may add small cooling fan, e.g. 12V/0.1-0.2A
5/ We should use R5 to R8 to monitor the current of the transistors.

Conclusions

That short paper is presenting dual universal hardware driver for embedded systems
The circuit may drive DC motors, incandescent bulbs, relays, loudspeakers, transformers, solenoids, inductors, LEDs, long cables, etc. but we should take considerations about the parameters of the loads and the implementation of the driver.

The control inputs S1, /S2, S3 and /S4 are TTL and CMOS compatible for control system working with 5V.

They can be driven directly from most of the MCUs.

There are two free inverters in 7406 and we may use them to obtain active LOW levels for the signals S1 and S3 or active HIGH levels for the signals /S2 and /S4 or for any other appropriate goals.


 

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